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

2021
Views:

425

Pages:

12
Author:

Brennen Smith

Is There a Germ Plasm in Mammals? Oct4 in ICM • No germ plasm yet identified in mammals – Induction by BMPs – Oct4 transcription factor: expressed in all early blastula cells, but then gradually restricted to just PGCs – Later only in oocytes (and spermatogonia) Oct4 Expression Pattern • Expression driven by Oct4 promoter in epiblast and migrating to gonad Oct4 Expression Pattern Spermatogonia Nuclei of Oogonia/Oocytes Therapeutic Cloning for Stem Cells – Construction of a cloned embryo from somatic cell of an adult patient – Culture to blastocyst stage to obtain ICM – Destruction of embryo to harvest stem cells – Growth in dish under appropriate conditions to control differentiation or in host Oct 4 and Adult Stem Cells • keeps cells pluripotent • pluripotent stem cells made directly from adult fibroblasts by the addition of four factors—Oct3/4, Sox2, c-Myc, and Klf4 DNA binding domain Migration of Primordial Germ Cells to the Gonads: Drosophila Pole cells in cellular blastoderm Pole cells in the posterior midgut invagination during gastrulation Germ Cell Repulsion • 1) passively carried by gastrulation • 2) gut endoderm triggers PGCs to move out – wunen protein expressed in endoderm – repels PGCs from endoderm so enter mesoderm Germ Cell Attraction • 3) PGCs migrate to gonads – (gonads are derived from lateral mesoderm) – columbus and hedgehog protein expressed by mesodermal gonad cells to help guide PGCs – mutants that lack clb • PGC not attracted to gonad – mutants that miss-express clb • PCG attracted to wrong place • 4) gonad coalesces around germ cells PGC Migration in Frogs • Ventral region of egg has determinants • In endodermal cells at posterior larval gut • Migrate along gut and into genital ridges • Crawl with filopodia over oriented fibronectin coated ECM • Modest proliferation until reach gonad (30 cells) • In newts, pgc’s are induced Nanos PGC Migration in Birds • PCGs accumulate in extraembryonic germinal crescent region and proliferate • Enter bloodstream • Carried to hindgut and deposited at region of genital ridge • Chemotaxis specifically to gonad rudiments in vitro Germ Cells Mammals • Germ cells are induced by BMPs, not set aside • Groups of responding cells express fragilis – transmembrane protein (proliferation?) • In center of cluster express stella (nuclei acid binding?) -> germ cells • Migrate into the endoderm, then gut, finally exiting into genital ridge Germ Cell Migration in Mammals • Migration between day 7 and day 12 • Divide as they migrate – (10-100 -> 2500-5000) – Stem cell factor stimulates proliferation • Move by extending filipodia – integrin - ECM (fibronectin) interactions? – Soluble chemo-attractants (TFG 1)?

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