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

2020
Views:

425

Pages:

15
Author:

Layla Bonilla

What Are Cell Differentiation and Cell Specification? • Development of differentiated cell types – different in function, cell shape, internal structures, proteins and biochemical pathways • Preceded by commitment to fate – Specification: can differentiate in neutral environment, but reversible in new environment – Determination: irreversible even in new environment What Are the Different Modes of Specification? • Autonomous Specification – Independent of other cells in embryo (selfdifferentiating parts) – Determined by internal cytoplasmic factors – If cleavage patterns are invariant, then cell fates will be invariant – “Mosaic” development – Characteristic of invertebrates What Are the Different Modes of Specification? • Conditional Specification (“Non-Autonomous”) – Depends on conditions (cell interactions) – More variable (variations in which cells are assigned which fates) – Capacity to “regulate” – Characteristic of vertebrates (and some invertebrates) What Are the Different Modes of Specification? • Syncitial Specification – Interactions between regions of cells before cellularization – Cells have no specific cell fate before cellularization – After cellularization, mostly conditional specification – Most insects Chabry’s Experiment 1887 • Mollusc • Certain cells form trochoblasts (ciliated) • In isolation • autonomous Roux’s Frog Cell Destruction Experiments (1888) • Defect experiment • Frog embryos • One blastomere makes only half of embryo • Support for autonomous specification? Tunicate Specification is Mostly Autonomous • Tunicate embryo – Isolation experiment – Separate 8 cell stage quadrants – Each forms only what it would have formed and does so autonomously Cytoplasm Contains Determinants Cytoplasmic Autonomy Extends to the Molecular Level • Tunicate Embryo (1977) – Isolated muscle forming cell lineage makes muscle acetylcholinesterase – If cytoplasm injected into isolated b4.2 causes it to make the enzyme Driesch’s Sea Urchin Isolation Experiments: Regulation (1892) • Sea urchin • Each blastomere gives rise to complete larva • Supports conditional specification Conditional Specification in Frog Transplantation Experiment • Cell fate according to new environment (A) – fate not fixed • Embryo makes up for what was taken away (B) – regulation Gradient of Fate-Determining Molecules in a Syncytial Embryo Stem Cells and Commitment • Cells that divide to form one copy of itself and one different – Pluripotent stem cells can lead to many cell types – Committed stem cells can lead to fewer types – Progenitor cells committed to one or few cell fates: not stem cells • Early cells have most potential (embryonic, fetal) Restriction of Potency with Time • Committed cells usually don’t change in new environment • Blood cell lineage: Mutants Identify Some Fatedetermining Molecules • What would be effect of a mutation in a fate-determining molecule? • These molecules must be acting very early – Packaged by the mother – Mutation in gene will influence the mother’s ability to make viable embryos – “Maternal-effect” genes

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