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#embryo

4 public questions tagged with this topic.

Specification Determination-ll

Which of the following outcomes was observed when the first two blastomeres (P1 and AB) of a C. elegans embryo were sepa

First cleavage in Caenorhabditis elegans partitions distinct cytoplasmic contents into AB and P1 blastomeres. P1 inherits PAR proteins, germ granules and maternal determinants like SKN-1 that autonomously activate endomesoderm gene regulatory networks, enabling isolated P1 to generate its normal repertoire of muscle, intestine and germline derivatives. AB alone produces only hypodermis and neurons, lacking pharyngeal lineages that require GLP-1/Notch signaling induced by P1 contact. This dichotomy illustrates that P1 fate is autonomously specified through inherited determinants, while AB lineage depends partially on conditional induction, highlighting mixed strategies within same embryo.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: C. elegans Early Cleavage and Autonomous Specification.

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Specification Determination-ll

If the blastomeres of a 4-cell stage sea urchin embryo are isolated, each forms a complete larva. This demonstrates:

Formation of a complete pluteus larva from a single isolated blastomere of a four-cell stage sea urchin embryo demonstrates classical conditional, regulative development. Fate is not prefixed by inherited determinants; instead, blastomeres continuously interpret positional information through Delta-Notch, Wnt/beta-catenin and Nodal signaling, adjusting lineage allocation to replace missing cells. Such compensation via community effect ensures robustness and whole-embryo regeneration from partial embryos. By contrast, mosaic embryos produce only partial structures upon blastomere isolation. Sea urchin results, pioneered by Hans Driesch, founded the concept of potency exceeding fate.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 3: Driesch Experiment and Conditional Specification.

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Fertilization in mammals-iv

Blastocoel formation depends on:

Blastocoel is fluid-filled cavity created within morula to form blastocyst. Its generation depends on establishment of functional epithelium by outer trophectoderm cells sealed by tight junctions. Basolateral Na/K ATPases actively transport sodium ions into intercellular space, creating osmotic gradient. Water follows via aquaporins, expanding microcavities into single blastocoel pushing inner cell mass eccentrically. Calcium is needed earlier for compaction and tight junctions, but sodium flux is direct driver of cavitation. Inhibition of Na/K pump with ouabain or removal of extracellular sodium blocks blastocoel formation, proving sodium gradient central to mammalian blastulation and embryonic fluid homeostasis.

Ref: Kim et al., Nat Comm 1998: Sodium pump mediated blastocoel formation in mammalian preimplantation embryos.

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