William Trevarrow | University of Oregon (original) (raw)

Papers by William Trevarrow

Development, May 1, 1988

In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be ide... more In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be identified appear as single cells or small clusters of cells, distributed periodically at intervals equal to the length of a somite. In the hindbrain, a series of neuromeres of corresponding length is present, and the earliest neurones are located in the centres of each neuromere. Young neurones within both the hindbrain and spinal cord were identified in live embryos using Nomarski optics, and histochemically by labelling for acetylcholinesterase activity and expression of an antigen recognized by the monoclonal antibody zn-1. Among them are individually identified hindbrain reticulospinal neurones and spinal motoneurones. These obervations suggest that early development in these regions of the CNS reflects a common segmental pattern. Subsequently, as more neurones differentiate, the initially similar patterning of the cells in these two regions diverges. A continuous longitudinal column of developing neurones appears in the spinal cord, whereas an alternating series of large and small clusters of neurones is present in the hindbrain.

Methods in Cell Biology, 2004

Publisher Summary This chapter outlines the current issues surrounding the construction, maintena... more Publisher Summary This chapter outlines the current issues surrounding the construction, maintenance, and use of genetically defined lines of zebrafish. The increasing number of zebrafish strains used for research raises a number of significant issues. Careful identification of zebrafish lines is critical in establishing the generality of research results. Each line of zebrafish is usually derived from a separate founder stock, and therefore each might harbor a unique genetic background. Through epistatic gene action, the genetic background of a given line can have marked effects on experimental results. Differences among the backgrounds of different wild-type lines could conceivably result in a given mutation displaying different phenotypes, which could have a variety of effects. This is particularly important in developmental biology because of the extensive use of forward genetic mutagenesis screens. The goals of a breeding program can be organized into three broad categories: genetic uniformity, maintenance of genetic variation, and selection for desirable phenotypes. Genetic monitoring of standard lines has made use of morphological, behavioral, immunological, and general line performance traits. Distribution of a line should provide the line's entire genetic background.

Development, Oct 1, 1988

Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are rev... more Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are reviewed. Segmented peripheral tissues include the trunk and tail myotomes, that are derived from somitic mesoderm, and the pharyngeal arches that are derived from head mesoderm in addition to other sources. Two major regions of the central nervous syst€ffi, the spinal cord and hindbrain, are also segmentally organized., as deduced from the distribution of identified neurones in both regions and by formation of neuromeres in the hindbrain that contain single sets of these neurones. Neural and mesodermal segments in the same body region can be related to one another by their patterns of motor innervation. This relationship is simple for the spinal f myotomal segments and com-r97 plex for the hindbrain/pharyngeal arch segments. Development of the segments is also complex. Mesodermal and ectodermal progenitors have separate embryonic origins and indeterminate cell lineageso and the embryonic cells migrate extensively before reaching their definitive segmental positions. Results of heat-shock experiments suggest that development of myotomal and spinal segments are regulated coordinately in postgastrula embryos. Segmental patterning may be a relatively late feature of zebrafish embryonic development.

Segmental pattern of development of the hindbrain and spinal cord of the zebrafish embryo. Develo... more Segmental pattern of development of the hindbrain and spinal cord of the zebrafish embryo. Development

Methods in Cell Biology, 2004

Publisher Summary This chapter outlines the current issues surrounding the construction, maintena... more Publisher Summary This chapter outlines the current issues surrounding the construction, maintenance, and use of genetically defined lines of zebrafish. The increasing number of zebrafish strains used for research raises a number of significant issues. Careful identification of zebrafish lines is critical in establishing the generality of research results. Each line of zebrafish is usually derived from a separate founder stock, and therefore each might harbor a unique genetic background. Through epistatic gene action, the genetic background of a given line can have marked effects on experimental results. Differences among the backgrounds of different wild-type lines could conceivably result in a given mutation displaying different phenotypes, which could have a variety of effects. This is particularly important in developmental biology because of the extensive use of forward genetic mutagenesis screens. The goals of a breeding program can be organized into three broad categories: genetic uniformity, maintenance of genetic variation, and selection for desirable phenotypes. Genetic monitoring of standard lines has made use of morphological, behavioral, immunological, and general line performance traits. Distribution of a line should provide the line's entire genetic background.

Methods in Cell Biology, 2004

Publisher Summary This chapter focuses on zebrafish facilities for small and large laboratories. ... more Publisher Summary This chapter focuses on zebrafish facilities for small and large laboratories. Common principles underlie all sizes of zebrafish facilities. Each facility has different research goals and available space. Efficient functioning and avoidance of failures are primary concerns. Greater control over potential negative outside influences such as water supply, air supply, food, and new fish increases stability and security. This has to be balanced with considerations of space, equipment cost, labor, cost of maintenance, staff technical abilities, research usefulness, as well as efforts invested in a particular fish line. A zebrafish facility can range in size from a few independently filtered aquarium setups, through one or more self-contained racks, each equipped with a common filtration system, to larger facilities with many tank racks and large separate filtration units. A new facility design provides a rare opportunity to more cheaply install an extensive centralization friendly infrastructure, such as specialized plumbing and electrical equipment. Fish containers (tanks) should be selected with several features in mind. Container size and desired population size will affect efficient space utilization and ease of use. Most people first encounter zebrafish in pet stores or home aquariums. Their hardiness, low maintenance, and ease of breeding make them good fish for beginners. These traits simplify maintaining large numbers of them without plenty of individual attention. Zebrafish can tolerate fairly wide extremes of environmental parameters. The water conditions can be maintained by hand or automatically with a water system.

Lab animal, 2002

PHS-funded and AAALAC-accredited facilities are required to use the Guide as the basis for settin... more PHS-funded and AAALAC-accredited facilities are required to use the Guide as the basis for setting up a zebrafish care and use program. The authors describe how they accomplished this task at the University of Oregon Zebrafish Facility.

The Journal of Comparative Neurology, 1990

This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells i... more This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells in the inner ear and the lateral line of the axolotl salamander, Ambystoma mexicanum. Zn-1 immunocytochemically labels the cytoplasm and stereocilia of mature hair cells in the sacculus, in the utriculus, and in the mechanoreceptive neuromast organs of the lateral line. Lower levels of labeling mark newly formed hair cells in the periphery of the sacculus and in regenerating neuromasts. Zn-1 also selectively labels neuronal processes and perikarya in the lateral line nerves and ganglia and the VIIIth cranial nerve and ganglion. Processes and perikarya are labeled by zn-1 in the dorsolateral medulla oblongata, a t sites of termination of the afferent octaval and lateral line neurons. Western blot analysis revealed that zn-1 labels one or more proteins with molecular weights of 80 and 160 kDa. The identity of these protein bands remains to be determined. The presence of a specific epitope expressed in both hair cells and neurons, but not in supporting cells, in the vestibular and auditory epithelia of the ear and in the mechanoreceptive neuromasts of the lateral line suggests shared cytogenetic heritages. These findings are consistent with a close evolutionary relationship between otic and lateral line senses, such as that inherent to the theoretical evolutionary scheme outlined in van Bergeijk's "acousticolateralis hypothesis." The protein recognized by zn-1 is as yet unidentified, but its conservative evolution suggests that it may serve an important function in the statoacoustic and lateral line systems.

Brain, Behavior and Evolution, 1998

Developmental processes present several problems for identifying homologies and analyzing their e... more Developmental processes present several problems for identifying homologies and analyzing their evolution. Most evolutionary techniques approach homologies from either a taxonomic or a molecular perspective. Approaches that can accommodate many problems of developmental evolution are not well developed. Developmental process and evolutionary lineage complexity lead to a number of largely unappreciated conceptual and analytic problems. Developmental processes can evolve by duplication or diversification. Each process is in a hierarchy of super- and subprocesses. As they evolve, process components may be exchanged with or acquired by those of other processes. Because they do not fit into standard analytic procedures, these situations (including reticulate or reticulate-appearing lineages, partial homologues, iterative features, and the tracing of nontaxonomic and nonmolecular evolutionary lineages) are often ignored or considered illegitimate. Biology's disdain for the dichotomously branching phylogenetic lineages that are the basis of standard analytic approaches is ignored at the risk of making falsely negative homology evaluations. I will present an approach that can accommodate analyses of these situations. The use of nontaxonomic and nonmolecular lineages provides a way to structure comparisons between other entities, as taxonomic lineages structure comparisons among potential homologues. From an informational point of view, any entity (either a structure or process) with an evolutionary history is a potential homologue with a potential evolutionary lineage. Comparing lineages of interacting entities can reveal topological incongruences among them. Methods that identify reticulated taxonomic and molecular lineages should also apply to other lineages. Partial homologues, resulting from reticulated lineages, can be handled in several possible ways. Analytically, such an entity can be treated as a partial homologue, a novel feature, an independent sub-unit, or a unitary feature homologous to the major contributor of its inherited features.

Development, 1988

In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be ide... more In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be identified appear as single cells or small clusters of cells, distributed periodically at intervals equal to the length of a somite. In the hindbrain, a series of neuromeres of corresponding length is present, and the earliest neurones are located in the centres of each neuromere. Young neurones within both the hindbrain and spinal cord were identified in live embryos using Nomarski optics, and histochemically by labelling for acetylcholinesterase activity and expression of an antigen recognized by the monoclonal antibody zn-1. Among them are individually identified hindbrain reticulospinal neurones and spinal motoneurones. These observations suggest that early development in these regions of the CNS reflects a common segmental pattern. Subsequently, as more neurones differentiate, the initially similar patterning of the cells in these two regions diverges. A continuous longitudinal column ...

Development, 1988

Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are rev... more Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are reviewed. Segmented peripheral tissues include the trunk and tail myotomes, that are derived from somitic mesoderm, and the pharyngeal arches that are derived from head mesoderm in addition to other sources. Two major regions of the central nervous system, the spinal cord and hindbrain, are also segmentally organized, as deduced from the distribution of identified neurones in both regions and by formation of neuromeres in the hindbrain that contain single sets of these neurones. Neural and mesodermal segments in the same body region can be related to one another by their patterns of motor innervation. This relationship is simple for the spinal/myotomal segments and complex for the hindbrain/pharyngeal arch segments. Development of the segments is also complex. Mesodermal and ectodermal progenitors have separate embryonic origins and indeterminate cell lineages, and the embryonic cells migra...

Neuron, 1990

To learn how neural segments are structured in a simple

Nature, 1995

The notochord is a midline mesodermal structure with an essential patterning function in all vert... more The notochord is a midline mesodermal structure with an essential patterning function in all vertebrate embryos. Zebrafish floating head (flh) mutants lack a notochord, but develop with prechordal plate and other mesodermal derivatives, indicating that flh functions specifically in notochord development. We show that floating head is the zebrafish homologue of Xnot, a homeobox gene expressed in the amphibian organizer and notochord. We propose that flh regulates notochord precursor cell fate.

Development, 1990

In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and rela... more In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and relatively simple set of ‘primary’ neurons that arise in the early embryo. We now have used monoclonal antibodies to show that, as they develop, primary neurons of several functional classes express on their surfaces the L2/HNK-1 tetrasaccharide that is associated with a variety of cell surface adhesion molecules. We have studied the early labeling patterns of these neurons, as well as some non-neural cells, and found that the time of onset and intensity of immunolabeling vary specifically according to cell type. The first neuronal expression is by Rohon-Beard and trigeminal ganglion neurons, both of which are primary sensory neurons that mediate touch sensitivity. These cells express the epitope very strongly on their growth cones and axons, permitting study of their development unobscured by labeling in other cells. Both types initiate axogenesis at the same early time, and appear to be th...

Developmental Biology, 1984

An arthropod leg represents a protuberance of the body segmental integument which bears distincti... more An arthropod leg represents a protuberance of the body segmental integument which bears distinctive markers in both the mediolateral and the anteroposterior axes. To clarify the biaxial organization of the body segmental morphogenetic field, and to study the relation among the whole-limb, limb segmental, and body segmental fields previously recognized in arthropods, we have grafted a proximal leg segment into the ventral midline in crayfish. After this operation the majority of animals regenerated a mirror-symmetric pair of supernumerary legs at the host site. Some of these legs had the most proximal segment, the coxa, partially fused to the adjacent body surface. Minority patterns of regeneration included one midline leg with a gill, three midline legs with a gill, and two normal legs with a third double-half leg. These results are compatible with the principle that intercalary regeneration restores the continuity of positional information.

Journal of Experimental …, 1983

Each leg of a crayfish embodies two types of morphogenetic fields, a limb field and a sequence of... more Each leg of a crayfish embodies two types of morphogenetic fields, a limb field and a sequence of segmental fields. These fields were manifest in grafting operations along the proximodistal axis of legs 3 and 4. The propodite was grafted into more proximal segment-arpopodite, meropodite, or basipodite-in one set of operations. In a second set the propodite was host for a graft from the propodite or carpopodite. After these operations intercalary regeneration yielded complete regenerates, which manifested the limb field, and incomplete regenerates, which showed the segmental field. Complete legs contained all structures present in a normal leg. After some operations complete legs also had supernumerary structures. Several types of incomplete legs regenerated-(1) legs with fusion of the host and graft segments; (2) legs with a joint girdling only part of the leg circumference; and (3) legs with one mosaic segment intercalated to replace two deleted segments. These results show that both limb and segmental fields control intercalation in the tested segments of crayfish legs, as in insect legs. We propose a "mode control hypothesis" to describe the way in which molt cycle phase and healing rate bias the type of field controlling regeneration. Our observations also provide clues about the operation of the fields to generate structures. Homologous parts of the segmental field do not necessarily generate analogous structures in different leg segments. Although intersegmental membrane often develops in conjunction with an apodeme (muscle tendon), in a mosaic joint intersegmental membrane can still develop in the absence of the corresponding apodeme. In a partial joint the length of the segments adjacent to the joint is subnormal, but greater than the length of the segments between which a joint is missing. The jointless region may limit the growth of the jointed region.

Wilhelm Roux's Archives of Developmental Biology, 1985

The tail fan of a crayfish consists of the caudal end of the body, the telson, and the most cauda... more The tail fan of a crayfish consists of the caudal end of the body, the telson, and the most caudal limbs, the uropods. We investigated the positional information in these structures with grafting operations. The uropods are biramous; they bifurcate to a lateral exopodite and a medial endopodite. After the distal part of a uropod ramus was grafted to the stump of a ramus, medio-lateral or dorso-ventral mismatch of surfaces provoked the production of supernumerary distal parts. Proximo-distal intercalation between exopodite and endopodite yielded a mosaic ramus. The results show that the two rami contain equivalent ramus fields in congruent orientation. The exopodite consists of basal and distal segments; each of these segments seems to have an equivalent segmental field.

Development, May 1, 1988

In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be ide... more In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be identified appear as single cells or small clusters of cells, distributed periodically at intervals equal to the length of a somite. In the hindbrain, a series of neuromeres of corresponding length is present, and the earliest neurones are located in the centres of each neuromere. Young neurones within both the hindbrain and spinal cord were identified in live embryos using Nomarski optics, and histochemically by labelling for acetylcholinesterase activity and expression of an antigen recognized by the monoclonal antibody zn-1. Among them are individually identified hindbrain reticulospinal neurones and spinal motoneurones. These obervations suggest that early development in these regions of the CNS reflects a common segmental pattern. Subsequently, as more neurones differentiate, the initially similar patterning of the cells in these two regions diverges. A continuous longitudinal column of developing neurones appears in the spinal cord, whereas an alternating series of large and small clusters of neurones is present in the hindbrain.

Methods in Cell Biology, 2004

Publisher Summary This chapter outlines the current issues surrounding the construction, maintena... more Publisher Summary This chapter outlines the current issues surrounding the construction, maintenance, and use of genetically defined lines of zebrafish. The increasing number of zebrafish strains used for research raises a number of significant issues. Careful identification of zebrafish lines is critical in establishing the generality of research results. Each line of zebrafish is usually derived from a separate founder stock, and therefore each might harbor a unique genetic background. Through epistatic gene action, the genetic background of a given line can have marked effects on experimental results. Differences among the backgrounds of different wild-type lines could conceivably result in a given mutation displaying different phenotypes, which could have a variety of effects. This is particularly important in developmental biology because of the extensive use of forward genetic mutagenesis screens. The goals of a breeding program can be organized into three broad categories: genetic uniformity, maintenance of genetic variation, and selection for desirable phenotypes. Genetic monitoring of standard lines has made use of morphological, behavioral, immunological, and general line performance traits. Distribution of a line should provide the line's entire genetic background.

Development, Oct 1, 1988

Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are rev... more Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are reviewed. Segmented peripheral tissues include the trunk and tail myotomes, that are derived from somitic mesoderm, and the pharyngeal arches that are derived from head mesoderm in addition to other sources. Two major regions of the central nervous syst€ffi, the spinal cord and hindbrain, are also segmentally organized., as deduced from the distribution of identified neurones in both regions and by formation of neuromeres in the hindbrain that contain single sets of these neurones. Neural and mesodermal segments in the same body region can be related to one another by their patterns of motor innervation. This relationship is simple for the spinal f myotomal segments and com-r97 plex for the hindbrain/pharyngeal arch segments. Development of the segments is also complex. Mesodermal and ectodermal progenitors have separate embryonic origins and indeterminate cell lineageso and the embryonic cells migrate extensively before reaching their definitive segmental positions. Results of heat-shock experiments suggest that development of myotomal and spinal segments are regulated coordinately in postgastrula embryos. Segmental patterning may be a relatively late feature of zebrafish embryonic development.

Segmental pattern of development of the hindbrain and spinal cord of the zebrafish embryo. Develo... more Segmental pattern of development of the hindbrain and spinal cord of the zebrafish embryo. Development

Methods in Cell Biology, 2004

Publisher Summary This chapter outlines the current issues surrounding the construction, maintena... more Publisher Summary This chapter outlines the current issues surrounding the construction, maintenance, and use of genetically defined lines of zebrafish. The increasing number of zebrafish strains used for research raises a number of significant issues. Careful identification of zebrafish lines is critical in establishing the generality of research results. Each line of zebrafish is usually derived from a separate founder stock, and therefore each might harbor a unique genetic background. Through epistatic gene action, the genetic background of a given line can have marked effects on experimental results. Differences among the backgrounds of different wild-type lines could conceivably result in a given mutation displaying different phenotypes, which could have a variety of effects. This is particularly important in developmental biology because of the extensive use of forward genetic mutagenesis screens. The goals of a breeding program can be organized into three broad categories: genetic uniformity, maintenance of genetic variation, and selection for desirable phenotypes. Genetic monitoring of standard lines has made use of morphological, behavioral, immunological, and general line performance traits. Distribution of a line should provide the line's entire genetic background.

Methods in Cell Biology, 2004

Publisher Summary This chapter focuses on zebrafish facilities for small and large laboratories. ... more Publisher Summary This chapter focuses on zebrafish facilities for small and large laboratories. Common principles underlie all sizes of zebrafish facilities. Each facility has different research goals and available space. Efficient functioning and avoidance of failures are primary concerns. Greater control over potential negative outside influences such as water supply, air supply, food, and new fish increases stability and security. This has to be balanced with considerations of space, equipment cost, labor, cost of maintenance, staff technical abilities, research usefulness, as well as efforts invested in a particular fish line. A zebrafish facility can range in size from a few independently filtered aquarium setups, through one or more self-contained racks, each equipped with a common filtration system, to larger facilities with many tank racks and large separate filtration units. A new facility design provides a rare opportunity to more cheaply install an extensive centralization friendly infrastructure, such as specialized plumbing and electrical equipment. Fish containers (tanks) should be selected with several features in mind. Container size and desired population size will affect efficient space utilization and ease of use. Most people first encounter zebrafish in pet stores or home aquariums. Their hardiness, low maintenance, and ease of breeding make them good fish for beginners. These traits simplify maintaining large numbers of them without plenty of individual attention. Zebrafish can tolerate fairly wide extremes of environmental parameters. The water conditions can be maintained by hand or automatically with a water system.

Lab animal, 2002

PHS-funded and AAALAC-accredited facilities are required to use the Guide as the basis for settin... more PHS-funded and AAALAC-accredited facilities are required to use the Guide as the basis for setting up a zebrafish care and use program. The authors describe how they accomplished this task at the University of Oregon Zebrafish Facility.

The Journal of Comparative Neurology, 1990

This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells i... more This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells in the inner ear and the lateral line of the axolotl salamander, Ambystoma mexicanum. Zn-1 immunocytochemically labels the cytoplasm and stereocilia of mature hair cells in the sacculus, in the utriculus, and in the mechanoreceptive neuromast organs of the lateral line. Lower levels of labeling mark newly formed hair cells in the periphery of the sacculus and in regenerating neuromasts. Zn-1 also selectively labels neuronal processes and perikarya in the lateral line nerves and ganglia and the VIIIth cranial nerve and ganglion. Processes and perikarya are labeled by zn-1 in the dorsolateral medulla oblongata, a t sites of termination of the afferent octaval and lateral line neurons. Western blot analysis revealed that zn-1 labels one or more proteins with molecular weights of 80 and 160 kDa. The identity of these protein bands remains to be determined. The presence of a specific epitope expressed in both hair cells and neurons, but not in supporting cells, in the vestibular and auditory epithelia of the ear and in the mechanoreceptive neuromasts of the lateral line suggests shared cytogenetic heritages. These findings are consistent with a close evolutionary relationship between otic and lateral line senses, such as that inherent to the theoretical evolutionary scheme outlined in van Bergeijk's "acousticolateralis hypothesis." The protein recognized by zn-1 is as yet unidentified, but its conservative evolution suggests that it may serve an important function in the statoacoustic and lateral line systems.

Brain, Behavior and Evolution, 1998

Developmental processes present several problems for identifying homologies and analyzing their e... more Developmental processes present several problems for identifying homologies and analyzing their evolution. Most evolutionary techniques approach homologies from either a taxonomic or a molecular perspective. Approaches that can accommodate many problems of developmental evolution are not well developed. Developmental process and evolutionary lineage complexity lead to a number of largely unappreciated conceptual and analytic problems. Developmental processes can evolve by duplication or diversification. Each process is in a hierarchy of super- and subprocesses. As they evolve, process components may be exchanged with or acquired by those of other processes. Because they do not fit into standard analytic procedures, these situations (including reticulate or reticulate-appearing lineages, partial homologues, iterative features, and the tracing of nontaxonomic and nonmolecular evolutionary lineages) are often ignored or considered illegitimate. Biology's disdain for the dichotomously branching phylogenetic lineages that are the basis of standard analytic approaches is ignored at the risk of making falsely negative homology evaluations. I will present an approach that can accommodate analyses of these situations. The use of nontaxonomic and nonmolecular lineages provides a way to structure comparisons between other entities, as taxonomic lineages structure comparisons among potential homologues. From an informational point of view, any entity (either a structure or process) with an evolutionary history is a potential homologue with a potential evolutionary lineage. Comparing lineages of interacting entities can reveal topological incongruences among them. Methods that identify reticulated taxonomic and molecular lineages should also apply to other lineages. Partial homologues, resulting from reticulated lineages, can be handled in several possible ways. Analytically, such an entity can be treated as a partial homologue, a novel feature, an independent sub-unit, or a unitary feature homologous to the major contributor of its inherited features.

Development, 1988

In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be ide... more In the ventral hindbrain and spinal cord of zebrafish embryos, the first neurones that can be identified appear as single cells or small clusters of cells, distributed periodically at intervals equal to the length of a somite. In the hindbrain, a series of neuromeres of corresponding length is present, and the earliest neurones are located in the centres of each neuromere. Young neurones within both the hindbrain and spinal cord were identified in live embryos using Nomarski optics, and histochemically by labelling for acetylcholinesterase activity and expression of an antigen recognized by the monoclonal antibody zn-1. Among them are individually identified hindbrain reticulospinal neurones and spinal motoneurones. These observations suggest that early development in these regions of the CNS reflects a common segmental pattern. Subsequently, as more neurones differentiate, the initially similar patterning of the cells in these two regions diverges. A continuous longitudinal column ...

Development, 1988

Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are rev... more Recent findings on the nature and origin of segmentation in zebrafish, Brachydanio rerio, are reviewed. Segmented peripheral tissues include the trunk and tail myotomes, that are derived from somitic mesoderm, and the pharyngeal arches that are derived from head mesoderm in addition to other sources. Two major regions of the central nervous system, the spinal cord and hindbrain, are also segmentally organized, as deduced from the distribution of identified neurones in both regions and by formation of neuromeres in the hindbrain that contain single sets of these neurones. Neural and mesodermal segments in the same body region can be related to one another by their patterns of motor innervation. This relationship is simple for the spinal/myotomal segments and complex for the hindbrain/pharyngeal arch segments. Development of the segments is also complex. Mesodermal and ectodermal progenitors have separate embryonic origins and indeterminate cell lineages, and the embryonic cells migra...

Neuron, 1990

To learn how neural segments are structured in a simple

Nature, 1995

The notochord is a midline mesodermal structure with an essential patterning function in all vert... more The notochord is a midline mesodermal structure with an essential patterning function in all vertebrate embryos. Zebrafish floating head (flh) mutants lack a notochord, but develop with prechordal plate and other mesodermal derivatives, indicating that flh functions specifically in notochord development. We show that floating head is the zebrafish homologue of Xnot, a homeobox gene expressed in the amphibian organizer and notochord. We propose that flh regulates notochord precursor cell fate.

Development, 1990

In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and rela... more In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and relatively simple set of ‘primary’ neurons that arise in the early embryo. We now have used monoclonal antibodies to show that, as they develop, primary neurons of several functional classes express on their surfaces the L2/HNK-1 tetrasaccharide that is associated with a variety of cell surface adhesion molecules. We have studied the early labeling patterns of these neurons, as well as some non-neural cells, and found that the time of onset and intensity of immunolabeling vary specifically according to cell type. The first neuronal expression is by Rohon-Beard and trigeminal ganglion neurons, both of which are primary sensory neurons that mediate touch sensitivity. These cells express the epitope very strongly on their growth cones and axons, permitting study of their development unobscured by labeling in other cells. Both types initiate axogenesis at the same early time, and appear to be th...

Developmental Biology, 1984

An arthropod leg represents a protuberance of the body segmental integument which bears distincti... more An arthropod leg represents a protuberance of the body segmental integument which bears distinctive markers in both the mediolateral and the anteroposterior axes. To clarify the biaxial organization of the body segmental morphogenetic field, and to study the relation among the whole-limb, limb segmental, and body segmental fields previously recognized in arthropods, we have grafted a proximal leg segment into the ventral midline in crayfish. After this operation the majority of animals regenerated a mirror-symmetric pair of supernumerary legs at the host site. Some of these legs had the most proximal segment, the coxa, partially fused to the adjacent body surface. Minority patterns of regeneration included one midline leg with a gill, three midline legs with a gill, and two normal legs with a third double-half leg. These results are compatible with the principle that intercalary regeneration restores the continuity of positional information.

Journal of Experimental …, 1983

Each leg of a crayfish embodies two types of morphogenetic fields, a limb field and a sequence of... more Each leg of a crayfish embodies two types of morphogenetic fields, a limb field and a sequence of segmental fields. These fields were manifest in grafting operations along the proximodistal axis of legs 3 and 4. The propodite was grafted into more proximal segment-arpopodite, meropodite, or basipodite-in one set of operations. In a second set the propodite was host for a graft from the propodite or carpopodite. After these operations intercalary regeneration yielded complete regenerates, which manifested the limb field, and incomplete regenerates, which showed the segmental field. Complete legs contained all structures present in a normal leg. After some operations complete legs also had supernumerary structures. Several types of incomplete legs regenerated-(1) legs with fusion of the host and graft segments; (2) legs with a joint girdling only part of the leg circumference; and (3) legs with one mosaic segment intercalated to replace two deleted segments. These results show that both limb and segmental fields control intercalation in the tested segments of crayfish legs, as in insect legs. We propose a "mode control hypothesis" to describe the way in which molt cycle phase and healing rate bias the type of field controlling regeneration. Our observations also provide clues about the operation of the fields to generate structures. Homologous parts of the segmental field do not necessarily generate analogous structures in different leg segments. Although intersegmental membrane often develops in conjunction with an apodeme (muscle tendon), in a mosaic joint intersegmental membrane can still develop in the absence of the corresponding apodeme. In a partial joint the length of the segments adjacent to the joint is subnormal, but greater than the length of the segments between which a joint is missing. The jointless region may limit the growth of the jointed region.

Wilhelm Roux's Archives of Developmental Biology, 1985

The tail fan of a crayfish consists of the caudal end of the body, the telson, and the most cauda... more The tail fan of a crayfish consists of the caudal end of the body, the telson, and the most caudal limbs, the uropods. We investigated the positional information in these structures with grafting operations. The uropods are biramous; they bifurcate to a lateral exopodite and a medial endopodite. After the distal part of a uropod ramus was grafted to the stump of a ramus, medio-lateral or dorso-ventral mismatch of surfaces provoked the production of supernumerary distal parts. Proximo-distal intercalation between exopodite and endopodite yielded a mosaic ramus. The results show that the two rami contain equivalent ramus fields in congruent orientation. The exopodite consists of basal and distal segments; each of these segments seems to have an equivalent segmental field.