Analysis of PHA-1 Reveals a Limited Role in Pharyngeal Development and Novel Functions in Other Tissues

Abstract

PHA-1 encodes a cytoplasmic protein that is required for embryonic morphogenesis and attachment of the foregut (pharynx) to the mouth (buccal capsule). Previous reports have in some cases suggested that PHA-1 is essential for the differentiation of most or all pharyngeal cell types. By performing mosaic analysis with a recently acquired pha-1 null mutation (tm3671), we found that PHA-1 is not required within most or all pharyngeal cells for their proper specification, differentiation, or function. Rather, our evidence suggests that PHA-1 acts in the arcade or anterior epithelial cells of the pharynx to promote attachment of the pharynx to the future buccal capsule. In addition, PHA-1 appears to be required in the epidermis for embryonic morphogenesis, in the excretory system for osmoregulation, and in the somatic gonad for normal ovulation and fertility. PHA-1 activity is also required within at least a subset of intestinal cells for viability. To better understand the role of PHA-1 in the epidermis, we analyzed several apical junction markers in pha-1(tm3671) homozygous embryos. PHA-1 regulates the expression of several components of two apical junction complexes including AJM-1–DLG-1/discs large complex and the classical cadherin–catenin complex, which may account for the role of PHA-1 in embryonic morphogenesis.

A maternal-effect selfish genetic element in Caenorhabditis elegans

“…Moreover, our results indicate that pha-1 is not an organ-specific differentiation gene, as originally proposed (15), but a zygotically expressed antidote, and sup-35 is a maternal-effect toxin rather than a suppressor of pha-1 . This major reinterpretation of the roles of pha-1 and sup-35 is strongly supported by multiple lines of evidence from previous studies (18–21). First, sup-35 overexpression phenocopies pha-1 mutations, showing that sup-35 is sufficient to cause embryonic lethality (19).…”

“…First, sup-35 overexpression phenocopies pha-1 mutations, showing that sup-35 is sufficient to cause embryonic lethality (19). Second, all defects associated with pha-1 mutations are suppressed by mutations in sup-35 (18–21). Third, when N2 hermaphrodites heterozygous for a deletion that includes both sup-35 and pha-1 ( tDf2/+) self, the 25% of their progeny that are homozygous for this deletion arrest as embryos with pharyngeal defects (16, 19).…”

A maternal-effect genetic incompatibility inCaenorhabditis elegans

“…The antidote, pha-1, was originally thought to be a developmental gene, in large part due to the specific pharyngeal defects observed in mutants (Schnabel and Schnabel 1990;Granato et al 1994;Okkema et al 1997;Fay et al 2004;Mani and Fay 2009). However, the precise role of pha-1 in embryonic development remained elusive and controversial (Mango 2009;Fay et al 2012;Kuzmanov et al 2014). Our results indicate that pha-1 pharyngeal defects are a direct consequence of sup-35 toxicity, and that sup-35 and pha-1 act as a selfish element, instead of being integral components of C. elegans embryonic development as originally suggested.…”

“…Moreover, our results indicate that pha-1 is not an organ-specific differentiation gene, as originally proposed (Schnabel and Schnabel 1990), but a zygotically expressed antidote, and sup-35 is a maternal-effect toxin rather than a suppressor of pha-1. This major reinterpretation of the roles of pha-1 and sup-35 is strongly supported by multiple lines of evidence from previous studies (Mani and Fay 2009;Fay et al 2012;Kuzmanov et al 2014;Polley et al 2014).…”

“…First, sup-35 overexpression phenocopies pha-1 mutations, showing that sup-35 is sufficient to cause embryonic lethality (Mani and Fay 2009). Second, all defects associated with pha-1 mutations are suppressed by mutations in sup-35 (Mani and Fay 2009;Fay et al 2012;Kuzmanov et al 2014;Polley et al 2014). Third, when N2 hermaphrodites heterozygous for a deletion that includes both sup-35 and pha-1 (tDf2/+) self, the 25% of their progeny that are homozygous for this deletion arrest as embryos with pharyngeal defects (Schnabel et al 1991;Mani and Fay 2009).…”