Zebrafish Development PDF

Source: Kimmel et al. 1995 Figure 11.35 Discoidal meroblastic cleavage in a zebrafish egg  EVL – Epithelial; will be sloughed off Deep cells – will form the embryo YSL – will direct cell movements during gastrulation Microtubules – will move maternally deposited determin...

Source: Kimmel et al. 1995 Figure 11.35 Discoidal meroblastic cleavage in a zebrafish egg  EVL – Epithelial; will be sloughed off Deep cells – will form the embryo YSL – will direct cell movements during gastrulation Microtubules – will move maternally deposited determinants  Maternal determinants establish DV axis in zebrafish in a manner similar to Xenopus Dorsalizing activity (e.g., inhibitors of β-catenin degradation) β-catenin localization to presumptive dorsal pole Activation of squint Kimelman Nature Reviews Genetics 7, 360–372 (May 2006) | doi:10.1038/nri1837  Xenopus and zebrafish use similar mechanisms to specify endoderm and mesoderm Frog Xnr Zebrafish squint and cyclops Induction of Induction of mesoderm mesoderm Kimelman Nature Reviews Genetics 7, 360–372 (May 2006) | doi:10.1038/nri1837 How would you determine if squint and Xnr are related?  Note the location of β-catenin: YSL nuclei. These are the zebrafish “equivalents” of Xnr These are the zebrafish “equivalents” BMP and Wnt inhibitors Xenopus and zebrafish establish their DV axis and organizer using similar molecular mechanisms Koppen and Heisenberg, 2005 Cell movements during gastrulation E-Cadherin (Attaches EVL to Deep Cells) Epiboly 4.5 - 5 hpf Figure 4.7 E-cadherin is required for epiboly in zebrafish No E-cad ½ E-cad  Source of mesoderm & endoderm in fish Germ Ring Delamination & Ingression Involution 6 hpf Involution  FISH FISH FISH FROG Formation of a dorsal (low) - ventral (high) BMP signaling gradient is thought to pattern the neuroectoderm and mesoderm along the DV axis. Koppen and Heisenberg, 2005  Specifying Endomesoderm: The Frog Endoderm Bottom line: In frogs (and Sox17 ? probably fish) endodermal factors specify the mesoderm VegT Xnr Brachyury Mesoderm (Nodal) & Eomesodermin MODEL FOR MESODERM SPECIFICATION IN FROG:  Mechanical Forces Activate Mesoderm Specifiers in the fish e.g., latrunculin A, nocodazole Brachyury (aka notail) No Brachyury Brachyury (No notail) (Notail) Casanova (sox32) and sox17 are endodermal markers Gilbert 9 ed. Fig. 7.43 Pezeron et al., 2008  In fish, Endodermal cell migration proceeds by way of a Nodal & Casanova-dependent random walk over the surface of the yolk: the experiments I. Enhancer trap screen identifies a locus involved in endoderm specification  Endodermal cell migration proceeds by way of a Nodal & Casanova-dependent random walk over the surface of the yolk: the experiments II. Activate GFP+/cas+ and RFP+/cas- embryos with Nodal ligands (e.g., Squint) III. Perform genetic mosaic analysis AP axis formation in zebrafish Notail Notail is the zebrafish equivalent of mammalian brachyury and Xenopus Xbra 112 MYrs Human Mouse 450 MYrs Zebrafish Recap of cell rearrangements during zebrafish gastrulation Involution and ingression  Anterior-posterior axis specification: All about the brain Cyp26: retinoic acid hydroxylase. Breaks down RA in the anterior end cyp26 cyp26 cyp26 FGF, Wnt Wnt and Fgf repress expression Cyp26 Otx2 of anterior genes