Thus, the animal vegetal polarity of the oocyte can be easily determined visually. The yolk platelets accumulate in the vegetal hemisphere of the oocyte, and the pigment granules accumulate along the cortex of the animal pole along with the germinal vesicle. After being surrounded by somatic follicle cells, these lampbrush chromosomes will recompact prior to the onset of vitellogenesis, the process by which yolk is imported from the liver via the circulation into the growing oocyte. Each primary oocyte will enter meiosis, during which huge extended chromosomes, called lampbrush chromosomes will form, indicating early activation of transcription. In contrast to Drosophila, each of the 16 cells generated by four rounds of mitoses in the primary oogonium will become a primary oocyte. The oocytes are very large, and develop from the primary oogonium. 10.Another important model organism in developmental biology is the African clawed frog, Xenopus laevis. Vangl2 directs the posterior tilting and asymmetric localization of motile primary cilia. Transient tissue-scale deformation coordinates alignment of planar cell polarity junctions in the mammalian skin. Planar cell polarity: global inputs establishing cellular asymmetry. Planar cell polarity enables posterior localization of nodal cilia and left-right axis determination during mouse and Xenopus embryogenesis. Cell flow reorients the axis of planar polarity in the wing epithelium of Drosophila. PCP is induced in the neuroectoderm by a signal from the dorsal lip and likely propagates across the tissue by a cell contact-mediated process.Īigouy, B., Farhadifar, R., Staple, D. (J) Planar induction of PCP during gastrulation. The images are representative of four to five independent experiments, each including two to six embryos per group. Scale bar, 60 µm, in H, also refers to H′,I and I′. Grey arrows show GFP-Pk3 crescent orientation. White dashed line indicates cell borders in (H). Images shown in H and I are proximal to the graft (within 150 µm) (labeled as anterior), whereas H′ and I′ are more distal, from the posterior region of the NP (labeled as posterior). Graft position is indicated by arrowheads in H and I. DBL (H,H′) or VE (I,I′) were grafted to the anterior NP at stage 12/12.5. (H–I′) Fluorescent images of NPs from DBL-graft recipient embryos (stage 15) expressing GFP-Pk3 and HA-Vangl2 (unlabeled). These data are representative of four to five independent experiments. Red numbers, number of aggregates per bin. (F,G) Rose plots quantify Vangl2 aggregate orientation within 150 µm from the graft. Scale bar, 70 µm, in D, also refers to E. Grey arrows indicate Vangl2 aggregate orientation. (D,E) GFP and Vangl2 immunostaining of NPs grafted with DBL (D, n=7) or VE (E, n=3) at stage 12/12.5. Yellow boxes approximate the regions shown in (D) and (E). (B,C) Brightfield images of neurula embryos grafted with DBL (B) and VE (C) (green) to the anterior NP. (A) Schematic of dorsal blastopore lip (DBL) and ventral fragment (VE) grafting experiment. Published by The Company of Biologists Ltd.ĭorsal blastopore lip grafts exhibit PCP-inducing activity. Xenopus embryos Dorsal blastopore lip Induction Neuroectoderm PCP Prickle3 Signaling Vangl2. These observations suggest that neuroectodermal PCP is not instructed by a preexisting molecular gradient but induced by a signal from the dorsal blastopore lip. The PCP cue did not depend on the orientation of the graft and was distinct from neural inducers. Tissue transplantations indicated that PCP is triggered in the neural plate by a planar cue from the dorsal blastopore lip. By imaging Vangl2 and Prickle3, we show that PCP is progressively acquired in the neural plate and requires a signal from the posterior region of the embryo. Here we investigate the Xenopus neural plate, a tissue that has been previously shown to exhibit PCP. Although the segregation of PCP components to opposite cell borders is believed to play a critical role in this pathway, whether PCP derives from egg polarity or preexistent long-range gradient, or forms in response to a localized cue, remains a challenging question. Coordinated polarization of cells in the tissue plane, known as planar cell polarity (PCP), is associated with a signaling pathway critical for the control of morphogenetic processes.
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