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#mammalian development

3 public questions tagged with this topic.

Fertilization in mammals-ll

Gastrulation in mammals begins at:

Mammalian gastrulation converts bilaminar disc of epiblast and hypoblast into three germ layers. It begins posteriorly with appearance of primitive streak, linear epithelial thickening where epiblast cells undergo epithelial to mesenchymal transition via Wnt and Nodal signaling, downregulating E-cadherin and ingressing to form mesoderm and definitive endoderm. Brachyury T marks ingressing cells. Node at anterior tip acts as organizer secreting antagonists patterning axis. Primitive streak therefore corresponds to blastopore of amphibians, initiating body plan formation, axis specification, gastrulation movements, germ layer segregation for organogenesis and patterning events.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Primitive streak and initiation of gastrulation in mammalian embryos.

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Fertilization in mammals-ll

Rotational cleavage in mammals occurs at division:

Mammalian cleavage is holoblastic and rotational pattern uniquely observed. First division is meridional producing two blastomeres. Second division shows rotational orientation where one blastomere divides meridionally and sister divides equatorially, resulting in orthogonal spindle axes producing transient asymmetry and slight asynchrony. This pattern from second cleavage onward distinguishes mammals from other vertebrates. Rotational divisions generate blastomeres with different inherited polarity cues influencing subsequent lineage allocation to inner cell mass versus trophectoderm, establishing early embryonic-abembryonic axis formation, initial patterning events and cellular heterogeneity for differentiation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Rotational cleavage pattern in mammalian embryos and blastomere polarity.

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Fertilization in mammals-iv

Totipotent cells in mammals include:

In mammals totipotency denotes ability to generate entire organism including both embryonic tissues and extraembryonic membranes like placenta. Zygote represents ultimate totipotent cell produced immediately after fertilization. Early cleavage blastomeres up to four to eight-cell stage retain this potential because lineage segregation, compaction and polarization have not yet occurred. After compaction outer cells activate Cdx2 and become trophoblast precursors while inner cells remain inner cell mass. Inner cell mass and embryonic stem cells derived from it are pluripotent, limited to embryonic lineages, not fully totipotent.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 5: Totipotency and early mammalian cleavage lineage restriction and regulative development.

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