Talk:Sea Squirt Development
|About Discussion Pages|
Cite this page: Hill, M.A. (2019, March 23) Embryology Sea Squirt Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Talk:Sea_Squirt_Development
Cell-cycle control in oocytes and during early embryonic cleavage cycles in ascidians
Int Rev Cell Mol Biol. 2012;297:235-64. McDougall A, Chenevert J, Dumollard R.
The completely transparent eggs and embryos of the ascidian Phallusia mammillata are well suited for imaging-based studies of how cell cycle control mechanisms have been integrated into the processes of meiosis, fertilization, and embryonic development. Several cell cycle-related issues that pertain to reproduction and development have been addressed using the ascidian model. For example, how are sperm-triggered calcium oscillations controlled by cell cycle kinases? How is chromosome segregation during meiosis regulated? What processes does the Mos/MAPK signaling cascade control in eggs in addition to CSF-mediated cell cycle arrest? Following fertilization ascidians blastomeres display cell cycle asynchrony, oriented cell division, and unequal cleavage resulting in the formation of a distinctive gastrula composed of precisely 112 cells. Here, we shall summarize these topics and where possible show how the mechanisms identified in ascidians compare to those identified in other organisms. Copyright © 2012 Elsevier Inc. All rights reserved.
Neurula rotation determines left-right asymmetry in ascidian tadpole larvae
Development. 2012 Apr;139(8):1467-75. Epub 2012 Mar 7.
Nishide K, Mugitani M, Kumano G, Nishida H. Source Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, Japan. (email@example.com)
Tadpole larvae of the ascidian Halocynthia roretzi show morphological left-right asymmetry. The tail invariably bends towards the left side within the vitelline membrane. The structure of the larval brain is remarkably asymmetric. nodal, a conserved gene that shows left-sided expression, is also expressed on the left side in H. roretzi but in the epidermis unlike in vertebrates. We show that nodal signaling at the late neurula stage is required for stereotypic morphological left-right asymmetry at later stages. We uncover a novel mechanism to break embryonic symmetry, in which rotation of whole embryos provides the initial cue for left-sided expression of nodal. Two hours prior to the onset of nodal expression, the neurula embryo rotates along the anterior-posterior axis in a counterclockwise direction when seen in posterior view, and then this rotation stops when the left side of the embryo is oriented downwards. It is likely that epidermis monocilia, which appear at the neurula rotation stage, generate the driving force for the rotation. When the embryo lies on the left side, protrusion of the neural fold physically prevents it from rotating further. Experiments in which neurula rotation is perturbed by various means, including centrifugation and sandwiching between glass, indicate that contact of the left epidermis with the vitelline membrane as a consequence of neurula rotation promotes nodal expression in the left epidermis. We suggest that chemical, and not mechanical, signals from the vitelline membrane promote nodal expression. Neurula rotation is also conserved in other ascidian species.
Patterning the ascidian nervous system: structure, expression and transgenic analysis of the CiHox3 gene
Development. 1999 Nov;126(21):4737-48.
Locascio A, Aniello F, Amoroso A, Manzanares M, Krumlauf R, Branno M. Source Department of Biochemistry and Molecular Biology, Stazione Zoologica Anton Dohrn, Villa Comunale, Italy. firstname.lastname@example.org.Abstract
Hox genes play a fundamental role in the establishment of chordate body plan, especially in the anteroposterior patterning of the nervous system. Particularly interesting are the anterior groups of Hox genes (Hox1-Hox4) since their expression is coupled to the control of regional identity in the anterior regions of the nervous system, where the highest structural diversity is observed. Ascidians, among chordates, are considered a good model to investigate evolution of Hox gene, organisation, regulation and function. We report here the cloning and the expression pattern of CiHox3, a Ciona intestinalis anterior Hox gene homologous to the paralogy group 3 genes. In situ hybridization at the larva stage revealed that CiHox3 expression was restricted to the visceral ganglion of the central nervous system. The presence of a sharp posterior boundary and the absence of transcript in mesodermal tissues are distinctive features of CiHox3 expression when compared to the paralogy group 3 in other chordates. We have investigated the regulatory elements underlying CiHox3 neural-specific expression and, using transgenic analysis, we were able to isolate an 80 bp enhancer responsible of CiHox3 activation in the central nervous system (CNS). A comparative study between mouse and Ciona Hox3 promoters demonstrated that divergent mechanisms are involved in the regulation of these genes in vertebrates and ascidians. PMID 10518491