par-2, a gene required for blastomere asymmetry in Caenorhabditis elegans, encodes zinc-finger and ATP-binding motifs.

Abstract

The par-2 gene of Caenorhabditi elgans functions in early embryogenesis to ensure an amme first cleavage and the segregation of cytoplasmic factors. Both processes appear to be required to generate daughter blastomeres with distinct developmental potential. We isolated an allele of par-2 by using a screen for maternal-effect lethal mutations in a strain known for its high frequency of transposition events. A transposable lement was found to be linked to this allele. Sequences lanig the site oftransposon insertion were cloned and found to rescue the par-2 mutant phenotype. DNA In the par-2 region hybridized to a 2.3-kb germ-liueenriched mRNA. The cDNA corresponding to this germ-lineenriched message was cloned, sequenced, and used to identify the molecular lesions associated with three par-2 alleles. Sequence analysis of the par-2 cDNA revealed that the predicted protein contained two distinct motifs found in other known proteins: an ATP-binding site and a cystelue-rich motif which identifies thepar-2 gene product as a member of a growing class of putative zinc-binding proteins.A class of genes has been identified that is required for the generation of asymmetry in the early embryo and whose mutant phenotype resembles the cytochalasin D-treated embryos described above (6). Mutations in any one of the five par genes (for partitioning-defective) result in embryos with defects in the pition of the first cleavage furrow, altered orientation of the spindle at the second cleavage, synchronous early cleavages, defects in P-granule localization, and altered expression of intestinal cell differentiation markers. All mutations in these five genes result in strict maternaleffect lethality; therefore maternal expression of the par genes is required during oogenesis in order to produce viable embryos.To gain further insight into the role of the par genes in cytoplasmic partitioning, molecular analysis ofthese genes is essential. As a step toward an understanding of the generation of asymmetry and cytoplasmic localization in the C. elegans embryo at the molecular level, we have isolated and sequenced the par-2 gene. 1 1 Early embryogenesis in the nematode Caenorhabditis elegans is characterized by a series of asymmetric cleavages. The initial asymmetry of the early embryo becomes apparent during the first cell cycle, at which time cytoplasmic factors thought to be required for the specification of cell fate are segregated. The first cleavage produces a larger, anterior cell (AB) and a smaller, posterior cell (P1) which differ from each other in many respects including the orientation of subsequent cleavage planes, the timing ofcell cycles, and the kinds of differentiated cell types they ultimately produce (1). For instance, germ-line-specific P granules are uniformly dispersed in one-cell embryos but become localized to the posterior cortex midway through the first cell cycle (2). At first cleavage, nearly all of the P granules are partitioned to the P1 blastomere. Furthermore, studies of gut development (3) have shown ...

A Genomewide Screen for Suppressors of par-2 Uncovers Potential Regulators of PAR Protein-Dependent Cell Polarity in Caenorhabditis elegans

“…The lw32 allele contains a stop codon in the middle of the par-2 coding sequence and was shown to behave as a strong loss of function (Levitan et al 1994;Boyd et al 1996). We found that 99.4 6 0.3 75.2 6 3.9 spat-3(gk22) 99.8 6 0.0 98.7 6 0.1 rpn-10(tm1180) 99.0 6 0.1 99.2 6 0.3 rpn-10(tm1349) 99.0 6 0.2 97.3 6 0.8 nos-3(q650); par-2(it5ts) 86.5 6 2.0 53.6 6 1.6 nos-3(q650); par-2(lw32) 54.6 6 4.7 b ND par-2(it5ts); spat-3(gk22) 86.6 6 2.2 22.9 6 5.9 par-2(lw32); spat-3(gk22)…”

TheC. eleganshomolog ofDrosophilaLethal giant larvae functions redundantly with PAR-2 to maintain polarity in the early embryo

“…LGL-1 is sufficient to rescue PAR-2 loss of function par-2(lw32) is a strong allele that produces a truncated PAR-2 protein of a predicted 233 amino acids (Levitan et al, 1994) that lacks the domain required for cortical localization (Hao et al, 2006). If LGL-1 and PAR-2 function redundantly, we hypothesized that overexpression of LGL-1 might be sufficient to rescue the lethality of par-2(lw32).…”

Widely Conserved Signaling Pathways in the Establishment of Cell Polarity

“…The products of the Par genes are quite diverse in function. Par-1 and Par-4 encode serine/threonine-directed protein kinases Watts et al 2000); Par-2 is a RING finger domain protein that may function as an E3 ubiquitin ligase (Levitan et al 1994); Par-3 and Par-6 are PDZ (PSD95/Dlg/ZO1) domain-containing proteins with scaffolding or adaptor functions (Etemad-Moghadam et al 1995;Hung and Kemphues 1999); Par-5 is a 14-3-3 protein that binds to phosphorylated serine and threonine residues (Morton et al 2002); and PKC-3 is an atypical protein kinase C (aPKC). With the exception of Par-2, all of the Par proteins and aPKC are conserved throughout the Metazoa.…”