Jurgen Schmich - Academia.edu (original) (raw)
Papers by Jurgen Schmich
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.
Programmed cell death is not only known as a mechanism mediating tissue destruction, but also as ... more Programmed cell death is not only known as a mechanism mediating tissue destruction, but also as an organismic tool for body shaping and regulation of morphological events during development. Here we report the tight and vital link of the most prominent form of programmed cell death, apoptosis, to one of the oldest, most basic, and most radical developmental processes, the metamorphosis of the marine hydrozoon Hydractinia echinata. Apoptosis, represented by DNA fragmentation, appears very early during metamorphosis, approximately 20 minutes post induction. It is then executed in a very distinct spatial and temporal pattern, including the removal or phagocytosis of a large number of larval cells prior to the appearance of stolons and tentacles. Our data indicate a developmental program striving to reduce all body parts that are no longer necessary, before reaching a distinct turning point, when the development of adult features is initiated. During these events, morphogenesis of basa...
The International Journal of Developmental Biology, 2010
A novel wingless gene was isolated from the marine colonial hydroid Hydractinia echinata. Alignme... more A novel wingless gene was isolated from the marine colonial hydroid Hydractinia echinata. Alignments and Bayesian inference analysis clearly assign the gene to the Wnt5A group. In line with data found for the brachyury ortholog of Hydractinia, He-wnt5A is expressed during metamorphosis in the posterior tip of the spindle-shaped planula larva, suggesting that the tip functions as a putative organizer during metamorphosis. Additionally, the outermost cells of the posterior tip are omitted from apoptosis during metamorphosis. In order to investigate this putative organizer function, we transplanted the posterior tip of metamorphosing animals into non-induced larvae and into primary polyps 24 h and 48 h of age. In larvae, the tip induced formation of a secondary axis. In polyps the building of ectopic head structures was induced. Based on our data on axis formation, on gene expression similar to the organizers of other species, and the absence of regular apoptosis, we conclude that the posterior tip of the Hydractinia larva has organizing activity during metamorphosis.
Marine Biology, 2006
Laboratory rearing and reconstruction of Laodicea undulata (Hydrozoa) life cycle led to the disco... more Laboratory rearing and reconstruction of Laodicea undulata (Hydrozoa) life cycle led to the discovery for the first time in Leptomedusae of the potential for ontogeny reversal, i.e. the medusa stage can asexually transform back into the polyp stage. In turn, each rejuvenated polyp stage can newly activate the standard developmental programme towards colony morphogenesis and budding of secondary medusae. These can be considered as clonemates of the initial medusa batch, since they originate by asexual processes. In combination with the ordinary medusa budding process, the potential for reverse development might represent a tool to increase jellyfish population growth rate during the favourable season, but eventually it does not avoid jellyfish to die. Comparably to polyembryony, reverse development leads to offspring multiplication from a single fertilization event, with a wider dispersal of each single genotype; eventually, it favours the enhancement of the overall genetic diversity at small spatial scale. The life cycle of L. undulata from the Mediterranean Sea is re-described, linking previously uncoupled descriptions of either the polyp or the early medusa stages. Taxonomic considerations of the genus Laodicea and a comparison among the known Mediterranean species are also provided.
Invertebrate Neuroscience, 2010
In planula larvae of the invertebrate Hydractinia echinata (Cnidaria, Hydrozoa), peptides of the ... more In planula larvae of the invertebrate Hydractinia echinata (Cnidaria, Hydrozoa), peptides of the GLWamide and the RFamide families are expressed in distinct subpopulations of neurons, distributed in a typical spatial pattern through the larval body. However, in the adult polyp GLWamide or RFamide-expressing cells are located at body parts that do not correspond to the prior larval regions. Since we had shown previously that during metamorphosis a large number of cells are removed by programmed cell death (PCD), we aimed to analyze whether cells of the neuropeptide-expressing larval nerve net are among those sacrificed. By immunohistochemical staining and in situ hybridization, we labeled GLWamide-and RFamide-expressing cells. Double staining of neuropeptides and degraded DNA (TUNEL analysis) identified some neurosensory cells as being apoptotic. Derangement of the cytoplasm and rapid destruction of neuropeptide precursor RNA indicated complete death of these particular sensory cells in the course of metamorphosis. Additionally, a small group of RFamidepositive sensory cells in the developing mouth region of the primary polyp could be shown to emerge by proliferation. Our results support the idea that during metamorphosis, specific parts of the larval neuronal network are subject to neurodegeneration and therefore not used for construction of the adult nerve net. Most neuronal cells of the primary polyp arise by de novo differentiation of stem cells commited to neural differentiation in embryogenesis. At least some nerve cells derive from proliferation of progenitor cells. Clarification of how the nerve net of these basal eumetazoans degenerates may add information to the understanding of neurodegeneration by apoptosis as a whole in the animal kingdom.
Developmental Biology, 2009
Hox and ParaHox (H/P) genes belong to evolutionary-sister clusters that arose through duplication... more Hox and ParaHox (H/P) genes belong to evolutionary-sister clusters that arose through duplication of a ProtoHOX cluster early in animal evolution. In contrast to bilaterians, cnidarians express, beside PG1, PG2 and Gsx orthologs, numerous Hox-related genes with unclear origin. We characterized from marine hydrozoans three novel Hox-related genes expressed at medusa and polyp stages, which include a Pdx/Xlox ParaHox ortholog induced 1 day later than Gsx during embryonic development. To reconstruct H/P genes' early evolution, we performed multiple systematic comparative phylogenetic analyses, which identified derived sequences that blur the phylogenetic picture, recorded dramatically different evolutionary rates between ParaHox and Hox in cnidarians and showed the unexpected grouping of [Gsx-Pdx/Xlox-PG2-PG3] families in a single metagroup distinct from PG1. We propose a novel more parsimonious evolutionary scenario whereby H/P genes originated from a [Gsx-Pdx/Xlox-PG2-PG3]-related ProtoHox gene, the «posterior» and «anterior» H/P genes appearing secondarily. The ProtoHOX cluster would have contained the three Gsx/PG2, Pdx/PG3, Cdx/PG9 paralogs and produced through tandem duplication the primordial HOX and ParaHOX clusters in the Cnidaria-Bilateria ancestor. The stronger constraint on cnidarian ParaHox genes suggests that the primary function of pre-bilaterian H/P genes was to drive cellular evolutionary novelties such as neurogenesis rather than axis specification.
Development Genes and Evolution, 2007
Many marine invertebrates reproduce through a larval stage. The settlement and metamorphosis of m... more Many marine invertebrates reproduce through a larval stage. The settlement and metamorphosis of most of the species are synchronised and induced by environmental organisms, mainly bacteria. The hydrozoan Hydractinia echinata has become a model organism for metamorphosis of marine invertebrates. In this species, bacteria, e.g. Pseudoalteromonas espejiana, are the natural inducers of metamorphosis. Like in other species of marine invertebrates, metamorphosis can be induced artificially by monovalent cations, e.g. Cs + . In this study, we present systematic data that metamorphosis-with both inducing compounds, the natural one from bacteria and the artificial one Cs + -are indeed similar with respect to (a) the morphological progression, (b) the localisation of the primary induction signal in the larva, (c) the pattern of apoptotic cells occurring during the initial 10 h of metamorphosis and (d) the disappearance of RFamidedependent immunocytochemical signals in sensory neurons during this process. However, a difference occurs during the development of the anterior end, insofar as apoptotic cells and settlement appear earlier in planulae induced with bacteria. Thus, basically, Cs + may be used as an artificial inducer, mimicking the natural process. However, differences in the appearance of apoptotic cells and in settlement raise the question of how enormous developmental plasticity in hydrozoans actually can be, and how this is related to the absence of malignant devolution in hydrozoans.
Development Genes and Evolution, 1998
The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon re... more The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon reception of the cues, internal signals have to be set in motion to convey information to all cells of the larvae. For hydrozoan larvae it was hypothesised that ectodermal neurosensory cells at the anterior part are those cells receptive of the inducer. Recently, it was shown that novel peptides with a common GLWamide terminus are found in Cnidaria. These peptides are located in a specific subset of the anterior sensory cells. It was hypothesised that the neuropeptides represent an internal signal coordinating the metamorphic process. In the current study we present further evidence for this hypothesis. Induction of metamorphosis is very specific for the GLWamide terminus and amidation is essential. The potency to metamorphose is strongly correlated with the presence of GLWamide-immunoreactive cell bodies. Our data fit our hypothesis about a very important role of GLWamides in the initiation of the morphogenetic processes very well.
Cell and Tissue Research, 1998
GLWamides are a recently described, novel family of neuropeptides in Cnidaria. Antibodies specifi... more GLWamides are a recently described, novel family of neuropeptides in Cnidaria. Antibodies specific for the GLWamide terminus have been raised and used to evaluate the occurrence and localisation of immunopositive material in various Cnidaria in order to determine whether GLWamides are present and to obtain a first impression of the possible regulatory role of these neuropeptides. GLWamide immunoreactivity has been found in all species tested and is not confined to distinct life stages but is present during most of the life cycle of the Cnidaria. Additionally, GLWamides are expressed by different nerve cells at different life stages. GLWamide-immunoreactive cells constitute a subset of the neural equipment. Overall our data suggest that GLWamides generally occur in the nervous system of Cnidaria and that these peptides are multifunctional. Putative functions other than the control of development include the regulation of nematocyst discharge, muscle contraction and the regulation of gastric function.
Background: 3D-scaffolds have been shown to direct cell growth and differentiation in many differ... more Background: 3D-scaffolds have been shown to direct cell growth and differentiation in many different cell types, with the formation and functionalisation of the 3Dmicroenvironment being important in determining the fate of the embedded cells.
The International Journal of Developmental Biology, 2007
Cnidarians are unique organisms in the animal kingdom because of their unequalled potential to un... more Cnidarians are unique organisms in the animal kingdom because of their unequalled potential to undergo reverse development (RD). The life cycle of some species can temporarily shift ordinary, downstream development from zygote to adult into the opposite ontogenetic direction by back-transformation of some life stages. The potential for RD in cnidarians offers the possibility to investigate how integrative signalling networks operate to control directionality of ontogeny (reverse vs. normal development). Striking examples are found in some hydrozoans, where RD of medusa bud or liberated medusa stages leads to rejuvenation of the post-larval polyp stage. Artificial stress may determine ontogeny reversal. We describe here the results of experimental assays on artificial induction of RD by different chemical and physical inducers on two marine hydrozoans, Turritopsis dohrnii and Hydractinia carnea, showing a different potential for RD. A cascade of morphogenetic events occurs during RD by molecular mechanisms and cellular patterns recalling larval metamorphosis. For the first time, we show here that exposure to cesium chloride (CsCl), an inducer of larval metamorphosis, may also induce RD, highlighting similarities and differences between these two master ontogenetic processes in cnidarians.
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.
Developmental biology by Jurgen Schmich
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.
Programmed cell death is not only known as a mechanism mediating tissue destruction, but also as ... more Programmed cell death is not only known as a mechanism mediating tissue destruction, but also as an organismic tool for body shaping and regulation of morphological events during development. Here we report the tight and vital link of the most prominent form of programmed cell death, apoptosis, to one of the oldest, most basic, and most radical developmental processes, the metamorphosis of the marine hydrozoon Hydractinia echinata. Apoptosis, represented by DNA fragmentation, appears very early during metamorphosis, approximately 20 minutes post induction. It is then executed in a very distinct spatial and temporal pattern, including the removal or phagocytosis of a large number of larval cells prior to the appearance of stolons and tentacles. Our data indicate a developmental program striving to reduce all body parts that are no longer necessary, before reaching a distinct turning point, when the development of adult features is initiated. During these events, morphogenesis of basa...
The International Journal of Developmental Biology, 2010
A novel wingless gene was isolated from the marine colonial hydroid Hydractinia echinata. Alignme... more A novel wingless gene was isolated from the marine colonial hydroid Hydractinia echinata. Alignments and Bayesian inference analysis clearly assign the gene to the Wnt5A group. In line with data found for the brachyury ortholog of Hydractinia, He-wnt5A is expressed during metamorphosis in the posterior tip of the spindle-shaped planula larva, suggesting that the tip functions as a putative organizer during metamorphosis. Additionally, the outermost cells of the posterior tip are omitted from apoptosis during metamorphosis. In order to investigate this putative organizer function, we transplanted the posterior tip of metamorphosing animals into non-induced larvae and into primary polyps 24 h and 48 h of age. In larvae, the tip induced formation of a secondary axis. In polyps the building of ectopic head structures was induced. Based on our data on axis formation, on gene expression similar to the organizers of other species, and the absence of regular apoptosis, we conclude that the posterior tip of the Hydractinia larva has organizing activity during metamorphosis.
Marine Biology, 2006
Laboratory rearing and reconstruction of Laodicea undulata (Hydrozoa) life cycle led to the disco... more Laboratory rearing and reconstruction of Laodicea undulata (Hydrozoa) life cycle led to the discovery for the first time in Leptomedusae of the potential for ontogeny reversal, i.e. the medusa stage can asexually transform back into the polyp stage. In turn, each rejuvenated polyp stage can newly activate the standard developmental programme towards colony morphogenesis and budding of secondary medusae. These can be considered as clonemates of the initial medusa batch, since they originate by asexual processes. In combination with the ordinary medusa budding process, the potential for reverse development might represent a tool to increase jellyfish population growth rate during the favourable season, but eventually it does not avoid jellyfish to die. Comparably to polyembryony, reverse development leads to offspring multiplication from a single fertilization event, with a wider dispersal of each single genotype; eventually, it favours the enhancement of the overall genetic diversity at small spatial scale. The life cycle of L. undulata from the Mediterranean Sea is re-described, linking previously uncoupled descriptions of either the polyp or the early medusa stages. Taxonomic considerations of the genus Laodicea and a comparison among the known Mediterranean species are also provided.
Invertebrate Neuroscience, 2010
In planula larvae of the invertebrate Hydractinia echinata (Cnidaria, Hydrozoa), peptides of the ... more In planula larvae of the invertebrate Hydractinia echinata (Cnidaria, Hydrozoa), peptides of the GLWamide and the RFamide families are expressed in distinct subpopulations of neurons, distributed in a typical spatial pattern through the larval body. However, in the adult polyp GLWamide or RFamide-expressing cells are located at body parts that do not correspond to the prior larval regions. Since we had shown previously that during metamorphosis a large number of cells are removed by programmed cell death (PCD), we aimed to analyze whether cells of the neuropeptide-expressing larval nerve net are among those sacrificed. By immunohistochemical staining and in situ hybridization, we labeled GLWamide-and RFamide-expressing cells. Double staining of neuropeptides and degraded DNA (TUNEL analysis) identified some neurosensory cells as being apoptotic. Derangement of the cytoplasm and rapid destruction of neuropeptide precursor RNA indicated complete death of these particular sensory cells in the course of metamorphosis. Additionally, a small group of RFamidepositive sensory cells in the developing mouth region of the primary polyp could be shown to emerge by proliferation. Our results support the idea that during metamorphosis, specific parts of the larval neuronal network are subject to neurodegeneration and therefore not used for construction of the adult nerve net. Most neuronal cells of the primary polyp arise by de novo differentiation of stem cells commited to neural differentiation in embryogenesis. At least some nerve cells derive from proliferation of progenitor cells. Clarification of how the nerve net of these basal eumetazoans degenerates may add information to the understanding of neurodegeneration by apoptosis as a whole in the animal kingdom.
Developmental Biology, 2009
Hox and ParaHox (H/P) genes belong to evolutionary-sister clusters that arose through duplication... more Hox and ParaHox (H/P) genes belong to evolutionary-sister clusters that arose through duplication of a ProtoHOX cluster early in animal evolution. In contrast to bilaterians, cnidarians express, beside PG1, PG2 and Gsx orthologs, numerous Hox-related genes with unclear origin. We characterized from marine hydrozoans three novel Hox-related genes expressed at medusa and polyp stages, which include a Pdx/Xlox ParaHox ortholog induced 1 day later than Gsx during embryonic development. To reconstruct H/P genes' early evolution, we performed multiple systematic comparative phylogenetic analyses, which identified derived sequences that blur the phylogenetic picture, recorded dramatically different evolutionary rates between ParaHox and Hox in cnidarians and showed the unexpected grouping of [Gsx-Pdx/Xlox-PG2-PG3] families in a single metagroup distinct from PG1. We propose a novel more parsimonious evolutionary scenario whereby H/P genes originated from a [Gsx-Pdx/Xlox-PG2-PG3]-related ProtoHox gene, the «posterior» and «anterior» H/P genes appearing secondarily. The ProtoHOX cluster would have contained the three Gsx/PG2, Pdx/PG3, Cdx/PG9 paralogs and produced through tandem duplication the primordial HOX and ParaHOX clusters in the Cnidaria-Bilateria ancestor. The stronger constraint on cnidarian ParaHox genes suggests that the primary function of pre-bilaterian H/P genes was to drive cellular evolutionary novelties such as neurogenesis rather than axis specification.
Development Genes and Evolution, 2007
Many marine invertebrates reproduce through a larval stage. The settlement and metamorphosis of m... more Many marine invertebrates reproduce through a larval stage. The settlement and metamorphosis of most of the species are synchronised and induced by environmental organisms, mainly bacteria. The hydrozoan Hydractinia echinata has become a model organism for metamorphosis of marine invertebrates. In this species, bacteria, e.g. Pseudoalteromonas espejiana, are the natural inducers of metamorphosis. Like in other species of marine invertebrates, metamorphosis can be induced artificially by monovalent cations, e.g. Cs + . In this study, we present systematic data that metamorphosis-with both inducing compounds, the natural one from bacteria and the artificial one Cs + -are indeed similar with respect to (a) the morphological progression, (b) the localisation of the primary induction signal in the larva, (c) the pattern of apoptotic cells occurring during the initial 10 h of metamorphosis and (d) the disappearance of RFamidedependent immunocytochemical signals in sensory neurons during this process. However, a difference occurs during the development of the anterior end, insofar as apoptotic cells and settlement appear earlier in planulae induced with bacteria. Thus, basically, Cs + may be used as an artificial inducer, mimicking the natural process. However, differences in the appearance of apoptotic cells and in settlement raise the question of how enormous developmental plasticity in hydrozoans actually can be, and how this is related to the absence of malignant devolution in hydrozoans.
Development Genes and Evolution, 1998
The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon re... more The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon reception of the cues, internal signals have to be set in motion to convey information to all cells of the larvae. For hydrozoan larvae it was hypothesised that ectodermal neurosensory cells at the anterior part are those cells receptive of the inducer. Recently, it was shown that novel peptides with a common GLWamide terminus are found in Cnidaria. These peptides are located in a specific subset of the anterior sensory cells. It was hypothesised that the neuropeptides represent an internal signal coordinating the metamorphic process. In the current study we present further evidence for this hypothesis. Induction of metamorphosis is very specific for the GLWamide terminus and amidation is essential. The potency to metamorphose is strongly correlated with the presence of GLWamide-immunoreactive cell bodies. Our data fit our hypothesis about a very important role of GLWamides in the initiation of the morphogenetic processes very well.
Cell and Tissue Research, 1998
GLWamides are a recently described, novel family of neuropeptides in Cnidaria. Antibodies specifi... more GLWamides are a recently described, novel family of neuropeptides in Cnidaria. Antibodies specific for the GLWamide terminus have been raised and used to evaluate the occurrence and localisation of immunopositive material in various Cnidaria in order to determine whether GLWamides are present and to obtain a first impression of the possible regulatory role of these neuropeptides. GLWamide immunoreactivity has been found in all species tested and is not confined to distinct life stages but is present during most of the life cycle of the Cnidaria. Additionally, GLWamides are expressed by different nerve cells at different life stages. GLWamide-immunoreactive cells constitute a subset of the neural equipment. Overall our data suggest that GLWamides generally occur in the nervous system of Cnidaria and that these peptides are multifunctional. Putative functions other than the control of development include the regulation of nematocyst discharge, muscle contraction and the regulation of gastric function.
Background: 3D-scaffolds have been shown to direct cell growth and differentiation in many differ... more Background: 3D-scaffolds have been shown to direct cell growth and differentiation in many different cell types, with the formation and functionalisation of the 3Dmicroenvironment being important in determining the fate of the embedded cells.
The International Journal of Developmental Biology, 2007
Cnidarians are unique organisms in the animal kingdom because of their unequalled potential to un... more Cnidarians are unique organisms in the animal kingdom because of their unequalled potential to undergo reverse development (RD). The life cycle of some species can temporarily shift ordinary, downstream development from zygote to adult into the opposite ontogenetic direction by back-transformation of some life stages. The potential for RD in cnidarians offers the possibility to investigate how integrative signalling networks operate to control directionality of ontogeny (reverse vs. normal development). Striking examples are found in some hydrozoans, where RD of medusa bud or liberated medusa stages leads to rejuvenation of the post-larval polyp stage. Artificial stress may determine ontogeny reversal. We describe here the results of experimental assays on artificial induction of RD by different chemical and physical inducers on two marine hydrozoans, Turritopsis dohrnii and Hydractinia carnea, showing a different potential for RD. A cascade of morphogenetic events occurs during RD by molecular mechanisms and cellular patterns recalling larval metamorphosis. For the first time, we show here that exposure to cesium chloride (CsCl), an inducer of larval metamorphosis, may also induce RD, highlighting similarities and differences between these two master ontogenetic processes in cnidarians.
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.
Canadian Journal of Zoology, 2004
Cnidarians have long been considered simple animals in spite of the variety of their complex life... more Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.