Asymmetric cell division and axis formation in the embryo

Abstract

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 P1. 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 P2 and EMS, the two daughters of P1, as well as between P2 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.

A Genomewide RNAi Screen for Genes That Affect the Stability, Distribution and Function of P Granules in Caenorhabditis elegans

“…RNAi depletions that cause early cell cycle arrest or altered cell division patterns and eventually embryonic lethality may lead to a diffuse or ''missegregated'' P-granule pattern. In fact, P granules have been used as a marker to study cell polarity for .20 years, and some examples of P-granule missegregation have been intensively studied (e.g., Gonczy and Rose 2005;Cowan and Hyman 2007). In our secondary and tertiary screens, we more closely examined whether a defective GFPTPGL-1 phenotype appeared to be correlated with abnormal nuclear morphology, embryo patterning defects, and/or early arrest (Table 1).…”

Mechanisms of spindle positioning: cortical force generators in the limelight

“…In one-cell C. elegans embryos, the spindle assembles in the cell center, but is displaced under the influence of intrinsic anterior-posterior (A-P) polarity cues toward the posterior during metaphase and anaphase, resulting in unequal division (Figure 2a) [14]. Genetic and RNAi-based functional genomic screens have led to the identification of two partially redundant Ga subunits, GOA-1 and GPA-16 (collectively referred to as Ga hereafter), of two essentially identical TPR/ GoLoco-domain proteins, GPR-1 and GPR-2 (hereafter jointly referred to as GPR-1/2) and of the large coiledcoil protein LIN-5 as being essential for proper spindle positioning in the nematode [15,16,17,18,19].…”

Computational and Systems Biology

“…27 These modules also share regulators like the homologs MEX-5 and MEX-6 and the homologs OMA-1 and OMA-2, which are involved in oogenesis and/or early embryogenesis, indicating that these modules might be coregulated (WormBase). 28,29 Module 34 contains most known regulatory interactions and is discussed in more detail below. In addition, we observed a known regulatory interaction between genes in module 141.…”