[
WormBook,
2005]
Asymmetric cell divisions play an important role in generating diversity during metazoan development. In the early C. elegans embryo, a series of asymmetric divisions are crucial for establishing the three principal axes of the body plan (AP, DV, LR) and for segregating determinants that specify cell fates. In this review, we focus on events in the one-cell embryo that result in the establishment of the AP axis and the first asymmetric division. We first describe how the sperm-derived centrosome initiates movements of the cortical actomyosin network that result in the polarized distribution of PAR proteins. We then briefly discuss how components acting downstream of the PAR proteins mediate unequal segregation of cell fate determinants to the anterior blastomere AB and the posterior blastomere P 1 . We also review how a heterotrimeric G protein pathway generates cortically based pulling forces acting on astral microtubules, thus mediating centrosome and spindle positioning in response to AP polarity cues. In addition, we briefly highlight events involved in establishing the DV and LR axes. The DV axis is established at the four-cell stage, following specific cell-cell interactions that occur between P 2 and EMS , the two daughters of P 1 , as well as between P 2 and ABp , a daughter of AB . The LR axis is established shortly thereafter by the division pattern of ABa and ABp . We conclude by mentioning how findings made in early C. elegans embryos are relevant to understanding asymmetric cell division and pattern formation across metazoan evolution.
[
Methods Cell Biol,
1995]
Sequence analysis of cosmids from C. elegans and other organisms currently is best done using the random or "shotgun" strategy (Wilson et al., 1994). After shearing by sonication, DNA is used to prepare M13 subclone libraries which provide good coverage and high-quality sequence data. The subclones are assembled and the data edited using software tools developed especially for C. elegans genomic sequencing. These same tools facilitate much of the subsequent work to complete both strands of the sequence and resolve any remaining ambiguities. Analysis of the finished sequence is then accomplished using several additional computer tools including Genefinder and ACeDB. Taken together, these methods and tools provide a powerful means for genome analysis in the nematode.