Dynamic microtubules at the vegetal cortex predict the embryonic axis in zebrafish (original) (raw)
Related papers
Dynamic microtubules and specification of the zebrafish embryonic axis
Current Biology, 1997
Background: The zebrafish is emerging as an important genetic system for the study of vertebrate development, and many zygotic mutations affecting embryogenesis have been isolated. The early events in development are under the control of maternal genes but are relatively unexplored. Here, the process of axis specification is investigated.
Microtubule arrays of the zebrafish yolk cell: organization and function during epiboly
Development, 1994
In zebrafish (Danio rerio), meroblastic cleavages generate an embryo in which blastomeres cover the animal pole of a large yolk cell. At the 500-1000 cell stage, the marginal blastomeres fuse with the yolk cell forming the yolk syncytial layer. During epiboly the blastoderm and the yolk syncytial layer spread toward the vegetal pole. We have studied developmental changes in organization and function during epiboly of two distinct microtubule arrays located in the cortical cytoplasm of the yolk cell. In the anuclear yolk cytoplasmic layer, an array of microtubules extends along the animal-vegetal axis to the vegetal pole. In the early blastula the yolk cytoplasmic layer microtubules appear to originate from the marginal blastomeres. Once formed, the yolk syncytial layer exhibits its own network of intercrossing mitotic or interphase microtubules. The microtubules of the yolk cytoplasmic layer emanate from the microtubule network of the syncytial layer. At the onset of epiboly, the ex...
BioArchitecture, 2015
In zebrafish embryos, factors involved in both axis induction and primordial germ cell (PGC) development are localized to the vegetal pole of the egg. However, upon egg activation axis induction factors experience an asymmetric off-center shift whereas PGC factors undergo symmetric animally-directed movement. We examined the spatial relationship between the proposed dorsal genes wnt8a and grip2a and the PGC factor dazl at the vegetal cortex. We find that RNAs for these genes localize to different cortical depths, with the RNA for the PGC factor dazl at a deeper cortical level than those for axis-inducing factors. In addition, and in contrast to the role of microtubules in the long-range transport of dorsal determinants, we find that germ line determinant transport depends on the actin cytoskeleton. Our results support a model in which vegetal cortex differential RNA transport behavior is facilitated by RNA localization along cortical depth and differential coupling to cortical transport.
PLoS Genetics, 2010
Although of fundamental importance in developmental biology, the genetic basis for the symmetry breaking events that polarize the vertebrate oocyte and egg are largely unknown. In vertebrates, the first morphological asymmetry in the oocyte is the Balbiani body, a highly conserved, transient structure found in vertebrates and invertebrates including Drosophila, Xenopus, human, and mouse. We report the identification of the zebrafish magellan (mgn) mutant, which exhibits a novel enlarged Balbiani body phenotype and a disruption of oocyte polarity. To determine the molecular identity of the mgn gene, we positionally cloned the gene, employing a novel DNA capture method to target region-specific genomic DNA of 600 kb for massively parallel sequencing. Using this technique, we were able to enrich for the genomic region linked to our mutation within one week and then identify the mutation in mgn using massively parallel sequencing. This is one of the first successful uses of genomic DNA enrichment combined with massively parallel sequencing to determine the molecular identity of a gene associated with a mutant phenotype. We anticipate that the combination of these technologies will have wide applicability for the efficient identification of mutant genes in all organisms. We identified the mutation in mgn as a deletion in the coding sequence of the zebrafish microtubule actin crosslinking factor 1 (macf1) gene. macf1 is a member of the highly conserved spectraplakin family of cytoskeletal linker proteins, which play diverse roles in polarized cells such as neurons, muscle cells, and epithelial cells. In mgn mutants, the oocyte nucleus is mislocalized; and the Balbiani body, localized mRNAs, and organelles are absent from the periphery of the oocyte, consistent with a function for macf1 in nuclear anchoring and cortical localization. These data provide the first evidence for a role for spectraplakins in polarization of the vertebrate oocyte and egg.
The EMBO Journal, 2012
By analysing the cellular and subcellular events that occur in the centre of the developing zebrafish neural rod, we have uncovered a novel mechanism of cell polarisation during lumen formation. Cells from each side of the neural rod interdigitate across the tissue midline. This is necessary for localisation of apical junctional proteins to the region where cells intersect the tissue midline. Cells assemble a mirror-symmetric microtubule cytoskeleton around the tissue midline, which is necessary for the trafficking of proteins required for normal lumen formation, such as partitioning defective 3 and Rab11a to this point. This occurs in advance and is independent of the midline cell division that has been shown to have a powerful role in lumen organisation. To our knowledge, this is the first example of the initiation of apical polarisation part way along the length of a cell, rather than at a cell extremity. Although the midline division is not necessary for apical polarisation, it confers a morphogenetic advantage by efficiently eliminating cellular processes that would otherwise bridge the developing lumen.
Development, 2018
Zebrafish germ plasm ribonucleoparticles (RNPs) become recruited to furrows of early zebrafish embryos through their association with astral microtubules ends. During the initiation of cytokinesis, microtubules are remodeled into a furrow microtubule array (FMA), which is thought to be analogous to the mammalian midbody involved in membrane abscission. During furrow maturation, RNPs and FMA tubules transition from their original distribution along the furrow to enrichments at the furrow distal ends, which facilitates germ plasm mass compaction. We show that nebel mutants exhibit reduced furrow-associated slow calcium waves (SCWs), caused at least in part by defective enrichment of calcium stores. RNP and FMA distal enrichment mirrors the medial-to-distal polarity of SCWs, and inhibition of calcium release or downstream mediators such as Calmodulin affects RNP and FMA distal enrichment. Blastomeres with reduced or lacking SCWs, such as early blastomeres in nebel mutants and wild-type blastomeres at later stages, exhibit medially bundling microtubules similar to midbodies in other cell types. Our data indicate that SCWs provide medial-to-distal directionality along the furrow to facilitate germ plasm RNP enrichment at the furrow ends.
Proceedings of the National Academy of Sciences, 1997
The dorsal-ventral axis in frog embryos is specified during the first cell cycle, when the cortex rotates relative to the cytoplasmic core along parallel microtubules associated with the core. Cytoplasmic transfer experiments suggest that dorsal determinants are transported 90؇ from the vegetal pole to the dorsal equator, even though the cortex rotates only 30؇. Here we show that, during rotation, small endogenous organelles are rapidly propelled along the subcortical microtubules toward the future dorsal side and that f luorescent carboxylated beads injected into the vegetal pole are transported at least 60؇ toward the equator. We also show that deuterium oxide, which broadens the zone of dorsalization even though it reduces the extent of rotation and is known to randomize the microtubules, also randomizes the direction of organelle transport. Moreover, -catenin, a component of the Wnt signaling pathway that possesses dorsalizing activity in Xenopus, colocalizes with subcortical microtubules at the dorsal side of the egg at the end of rotation. We propose that cortical rotation functions to align subcortical microtubules, which then mediate the transport of dorsal determinants toward their plus ends on one side of the egg.