University:
Amherst College
Course:
BIOL 220 | Developmental Biology
Academic year:

2023
Views:

432

Pages:

21
Author:

Clinton Benson

Mammals Mammalian Development • • • • • • Rotational cleavage Slow cell division (1 day cycles) Asynchronous Early zygotic gene activation Adaptations for internal development Implantation of blastocyst Rotational Cleavage of Mammals Fertilization to Implantation Hatching Implantation Fate Map • 8-cell compaction -> 16-cell inner and outer – outer become trophoblast -> chorion (part of placenta) – inner cell mass -> embryo, yolk sac, amnion, allantois • Trophoblast allows uterine implantation • ICM -> blastocyst with blastocoele Derivation of Mammalian Tissues How Does Embryo Implant? Attachment to endometrium of uterus Digestion of endometrium ECM and invasion What Characterizes Mammalian Gastrulation? • Cell movements like birds and reptiles but no yolk • Chorion forms placenta to get maternal nutrients • Amnion protects embryo • Yolk sac underdeveloped Amnion Formation and Gastrulation Movements Similar to chick, some variation. Notochord Formation What is Origin of A-P Axis? • Two signaling centers – node (body and forebrain) – anterior visceral endoderm (forebrain) • Analogous to chick and frog organizers – signaling molecules wnts, bmps, fgfs – eventually noggin, chordin, cerberus, etc. Node and AVE 7d 8d mouse Are There More Homologies? Patterning Along A-P Axis • Hox Genes – – – – homologous to fly homeotic genes same order anterior to posterior 4 sets instead of one by gene by two duplications • A combinatorial code specifies identity Mammalian Hox Clusters Hox Spatial Expression: Fly vs. Mouse What is Origin of Dorsal-Ventral Axis? • Dorsal is from cells contacting the trophoblast and ventral is from cells near blastocoele • Egg A-V axis is perpendicular to embryonic-abembryonic axis (from oocyte?) – Dorsal at embryonic pole Dorsal-Ventral Axis What is Origin of Left-Right Chick Axis? • Cilia in node – Cause flow right to left – KO (dynein ciliary motor protein) – sterile males – random heart position • Symmetry breaking mechanism • Downstream targets Nodal, Pitx2 on left Mammal Nodal Vesicle Parcels • NVS secreted from node because of an FGF signal – Contain Shh and retinoic acid • Swept to left – Shh and RA same chick – Increase in Ca++ signal on left NC-Nieukoop center SMO-Speeman Mangold organizer Vertebrate Patterns Human Embryo 50 Days • Read “Sidelights and Speculations” Twins and Embryonic Stem Cells

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