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#early development

6 public questions tagged with this topic.

Stem Cell -ll

The cells of the 4-cell stage mouse embryo are:

Mammalian embryo displays highly regulative development: early blastomeres retain remarkable flexibility and equipotency. Murine four-cell embryo blastomeres remain totipotent as demonstrated by ability of isolated single cell to contribute to both trophectoderm and inner cell mass compartments and to support full-term development when aggregated with carrier cells or transplanted into foster mothers. Single-nucleus RNA sequencing shows equal expression of Oct4 and Cdx2 potentiality. Potency restriction occurs at compaction and blastocyst stage when Cdx2 and Oct4 become mutually exclusive, separating trophoblast from pluripotent inner cell mass lineage irreversibly.

Ref: Tarkowski, Nature 1959; Tarkowski & Wroblewska 1967: Mouse 4-cell blastomeres totipotent contribution.

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Elegans -ll

Which motor protein is responsible for P-granule migration?

P-granules, ribonucleoprotein assemblies marking germline, segregate to posterior blastomere P1 during first division and subsequently to germline precursors P2-P4. Their posterior migration along cell cortex before division requires microtubule motor dynein transporting granule components along cortical microtubules toward centrosome at posterior pole. PAR-1 dependent microtubule organization creates flow. Mutants in dynein heavy chain dhc-1 or its regulator dynactin cause equal distribution of P-granules to both AB and P1, losing germline restriction. Myosin II and kinesin contribute to cortical flows but dynein-driven transport is primary driver ensuring germ plasm inheritance by germline lineage.

Ref: Updike & Strome 2010; Gilbert Chapter 4: Dynein motor responsible for P-granule migration in early embryo.

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Drosophila -l

Early development before MBT in Drosophila is governed by:

During early Drosophila development before cycle 14, zygotic genome remains largely quiescent with only minor early zygotic genes transcribed. Embryo relies entirely on maternal products loaded during oogenesis by nurse cells, including mRNAs for bicoid, nanos, dorsal, gurken, and histones supporting rapid mitoses. These maternal determinants drive syncytial divisions, nuclear migrations, axis establishment and positional information. Activation of gap genes, pair-rule genes and cellularization requires maternal gradient interpretation. Therefore early patterning, cleavage and axis specification before maternal-to-zygotic transition are governed by maternal genes inherited from oocyte.

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 22: Maternal control of early development.

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Drosophila -l

Drosophila early development involves formation of:

Drosophila exhibits superficial cleavage where nuclear division occurs without cytoplasmic division. Zygote nucleus undergoes rapid synchronous mitoses within central cytoplasm, producing multinucleate syncytium. Around nuclear cycle 10, nuclei migrate peripherally into cortical cytoplasm, arranging beneath plasma membrane. Actin caps form above each nucleus, but no cell membranes separate nuclei, defining syncytial blastoderm. Only at cycle 14 does membrane invagination occur simultaneously around every cortical nucleus, converting syncytium into cellular blastoderm of epithelial monolayer surrounding central yolk. This syncytial stage allows rapid diffusion of morphogens like Bicoid essential for patterning.

Ref: NCBI, Molecular Biology of the Cell, Chapter 22: Syncytial blastoderm in Drosophila.

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Fertilization in mammals-lll

Successful compaction from morula to blastula involves:

Compaction to form morula requires establishment of strong cell-cell adhesion mediated by E-cadherin, a calcium-dependent adhesion molecule. Extracellular calcium rigidifies cadherin repeats enabling trans-homophilic binding between blastomeres, intracellularly binding beta-catenin which links to alpha-catenin and actin cytoskeleton. Activation and clustering of this cadherin-catenin complex drives blastomere flattening, polarization, tighter apposition and induction of tight junction formation. Blockage of cadherin or removal of calcium prevents compaction, while calcium ionophores alone without cadherin function insufficient. Successful compaction therefore depends on coordinated calcium influx and functional cadherin-beta-catenin assembly orchestrating Hippo pathway mediated lineage segregation.

Ref: Maître JL et al., Nature Cell Biology 2015: E-cadherin beta-catenin regulation of compaction and Hippo mediated cell fate.

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