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UNT BIOL 4330 - Mammalian Development
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BIOL 4330 1st Edition Lecture 9 Outline of Last Lecture I. Chick DevelopmentII. GastrulationIII. Epiboly of the EctodermIV. The Chick Organizera. FGFsOutline of Current Lecture I. Signaling CentersII. Hox GenesIII. Major Themes in Vertebrate GastrulationIV. Same Molecules Same AxesCurrent LectureThe membranes of the amniote egg characterize reptiles, birds, and mammals.Rotational cleavage: first cleavage is meridional and in the second one of the two blastomeres divides meridionally and the other equatorially (very different from most other patterns of embryonic division. Asynchonous cell division: unequal numbers of cells. Zygotic genes activated early 4-8 cell stage.The trophoblast or ICM is the first decision of the rest of your life. Core transcriptional circuitry for the pluripotency of ES cells. Prior to blastocyst formation, each embryonic blastomeres expresses both the Cdx2 and the Oct4 TFs and can become trophoblast or ICM but once the decision to be trophoblast or ICM is made the cell expresses a set of genes specific to each region.Retaining uncommitted pluripotent fates of embryonic mouse cells: The earliest blastomeres of the 8-cell embryo can form both trophoblast cells and the embryonic precursors (inner cell mass ICM). They are totipotent (capable of everything). The inner cells mass (ICM which gives rise to the embryos) are pluripotent (capable of many things).The first segregation of cells within the inner cell mass forms two layers: lower layer is the hypoblast and the remaining inner cell mass tissue above it is the epiblast. ICM delaminates hypoblast cells that line theblastocoel, forming the extraembryonic endoderm of the primitive yolk-sac and 2-layered (epiblast and These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.hypoblast) blastodisc. The trophoblast which will form the villi and the synctiotrophoblast, which will form uterine tissue.The placenta has both a maternal portion (uterine endometrium) or deciduas and a fetal component (the chorion). Mouse epiblast is cup-shaped vs disc shaped as in humans. Two signaling centers: 1st in node, 2nd in AVE (anterior visceral endoderm).Embryonic Day 7Two signaling centers: 1) In the node (Henson’s node = trunk portion of the amphibian organizer); gradient of Fgf8, RA from posterior to anterior 2) In the anterior visceral endoderm (AVE -to the chick hypoblast and to the head portion of the amphibian organizer) - no Nodal, BMPs, FGFs, Wnts. - Dorsal surface of the epiblast (embryonic ectoderm) is in contact with the amnionic cavity - Ventral surface of the epiblast contacts the newly formed mesoderm - the endoderm covers the embryo- Node is at the bottom of the cup and has generated the chordamesoderm-Two signaling centers, the node and the anterior visceral endoderm are oppositeChordin – seen in the anterior primitive streak, node and axial mesoderm (BMP antagonist)FGF gradients work through Cdx genes which integrate posteriorization and activate hox genes.RA, Wnt3a and Fgf8 each contribute to posterior patterning but are integrated through the Cdx (mammalian homologue of the fly Caudal genes) family of proteins that regulates the activity of Hox genes.Hox genes – evolutionary conservation of homeotic gene organization and transcription expression. All of the known mammalian genomes contain 4 copies of the Hox complex per haploid set located on 4 different xsomes. In all vertebrates anterior-posterior polarity becomes specified by the expression of Hox genes = homeotic selector genes (Hom-C).Hox genes are responsive to RA either by having RA receptors or by being responsive to Cdx which is activated by RA.After 5th cell division the blastocyst cavity begins to form and the ICM resides on 1 side of the cavity – hypoblast on the side exposed to blastocyst fluid, while dorsal axis forms from those ICM cells in contactwith trophoblast and amnion Dorsal-ventral axis of the embryo is defined by the embryonic (ICM)=abembryonic (part of the blastocystopposite ICM) axis of the blastocyst.Major Themes in Vetebrate Gastrulation1. Internalization of the endoderm and mesoderm2. Epiboly of the ectoderm around the entire embryo3. Convergence of the internal cells to the midline4. Extension of the body along the anterior-posterior axesSame Molecules to Accomplish Same Axes- Gradients of Nodal proteins to establish polarity along the dorsal-ventral axis- Each group uses BMP inhibitors to specify the dorsal axis, but use them in different ways- Wnt inhibition and Oxt2 expression are important in specifying anterior regions (but different groups of cells expressing these proteins differ among taxa)- In all Hox genes specify ant-post axes in all- L-R axes established through expression of Nodal on the L-side, activates Pitx2 leads to differences between left and right sides of the embryo – how Nodal becomes expressed on the L-side differs between vertebrate


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UNT BIOL 4330 - Mammalian Development

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