Journal
DEVELOPMENT
Volume 128, Issue 21, Pages 4301-4314Publisher
COMPANY OF BIOLOGISTS LTD
Keywords
asymmetric cell division; cell polarity; centrosome position; mesectoderm; mesendoderm; microtubules; PAR proteins
Categories
Funding
- NIGMS NIH HHS [R01GM49869] Funding Source: Medline
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C. elegans embryogenesis begins with a stereotyped sequence of asymmetric cell divisions that are largely responsible for establishing the nematode body plan. These early asymmetries are specified after fertilization by the widely conserved, cortically enriched PAR and PKC-3 proteins, which include three kinases and two PDZ domain proteins. During asymmetric cell divisions in the early embryo, centrosome pairs initially are positioned on transverse axes but then rotate to align with the anteroposterior embryonic axis. We show that rotation of the centrosomal/nuclear complex in an embryonic cell called P-1 requires a maternally expressed gene we name spn-4. The predicted SPN-4 protein contains a single RNA recognition motif (RRM), and belongs to a small subfamily of RRM proteins that includes one Drosophila and two human family members. Remarkably, in mutant embryos lacking spn-4 function the transversely oriented 'P-1' mitotic spindle appears to re-specify the axis of cell polarity, and the division remains asymmetric. spn-4 also is required for other developmental processes, including the specification of mesendoderm, the restriction of mesectoderm fate to P-1 descendants, and germline quiescence during embryogenesis. We suggest that SPN-4 post-transcriptionally regulates the expression of multiple developmental regulators. Such SPN-4 targets might then act more specifically to generate a subset of the anterior-posterior asymmetries initially specified after fertilization by the more generally required PAR and PKC-3 proteins.
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