3/12/2024 0 Comments Dorsal lip of blastopore nieuwkoop![]() 1997), and both tissues show a potent secondary axis-inducing ability upon transplantation (Spemann and Mangold 1924 Leikola, 1976). 1993 Smith and Harland 1992 Connolly et al. For example, the amphibian dorsal blastopore lip and the chick Hensen’s node express the same genes, such as goosecoid and noggin (Cho et al. While the molecular mechanisms involved in gastrulation are thought to be conserved among vertebrates, the morphogenetic movement is described as divergent. Gastrulation is a critical developmental event for producing three germ layers, three body axes, and the central nervous system in the embryo. Finally, by comparing amphibian gastrulation to gastrulation of protochordates and amniotes, we discuss the gastrulation movement evolutionarily conserved among chordates. Collectively, these results are consistent with the S&Z gastrulation model and identify the embryonic region sufficient for construction of the complete dorsal structure. Furthermore, a blastocoel roof explant of the blastula, which should contain the organizer and the prospective neuroectoderm in the S&Z model, autonomously underwent gastrulation and formed the complete dorsal structure. To investigate this possibility, we conducted stepwise tissue deletions using Xenopus laevis embryos and revealed that the dorsal one-third of the marginal zone had the ability to form the complete dorsal structure by itself. According to this model, the body axis is derived from limited regions of the dorsal marginal zone at ACE. The developmental stage when contact between the head organizer and the anterior-most neuroectoderm is established is called “anterior contact establishment (ACE).” After ACE, the A-P body axis elongates posteriorly. In this model, the organizer and the prospective neuroectoderm are originally localized in the blastula’s blastocoel roof, and these embryonic regions move downward to make physical contact of their inner surfaces with each other at the dorsal marginal zone. Previously, we proposed a novel amphibian gastrulation model, the “subduction and zippering (S&Z) model”. However, the morphological movement during gastrulation appears to be divergent across species, making it difficult to discuss the evolution of the process. ![]() ![]() One such candidate gene, noggin, is sufficient for rescuing development of irradiated embryos when its mRNA is injected (C).Gastrulation is a critical event whose molecular mechanisms are thought to be conserved among vertebrates. Establishment of cDNA libraries from extracted dorsal lip mRNA identified candidate genes that may be responsible for neural induction. Injection of extracted mRNA from the dorsal lip into irradiated Xenopus embryos rescued neural induction and overall development demonstrating there is a genetic basis of neural induction (B). Figure 1: Mangold's dorsal lip transplant experiment in Xenopus demonstrated that a transplanted dorsal lip could induce the formation of a double axis in the new host embryo, solidifying the dorsal lip's sufficiency in neural induction (A). It is particularly important for its role in neural induction through the default model, where signaling from the dorsal lip protects a region of the epiblast from becoming epidermis, thus allowing it to develop to its default neural tissue. The dorsal lip is formed during early gastrulation as folding of tissue along the involuting marginal zone of the blastocoel forms an opening known as the blastopore. The dorsal lip of the blastopore is a structure that forms during early embryonic development and is important for its role in organizing the germ layers. ![]()
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