lin-8, Which Antagonizes Caenorhabditis elegans Ras-Mediated Vulval Induction, Encodes a Novel Nuclear Protein That Interacts With the LIN-35 Rb Protein

Abstract

Ras-mediated vulval development in C. elegans is inhibited by the functionally redundant sets of class A, B, and C synthetic Multivulva (synMuv) genes. Three of the class B synMuv genes encode an Rb/DP/E2F complex that, by analogy with its mammalian and Drosophila counterparts, has been proposed to silence genes required for vulval specification through chromatin modification and remodeling. Two class A synMuv genes, lin-15A and lin-56, encode novel nuclear proteins that appear to function as a complex. We show that a third class A synMuv gene, lin-8, is the defining member of a novel C. elegans gene family. The LIN-8 protein is nuclear and can interact physically with the product of the class B synMuv gene lin-35, the C. elegans homolog of mammalian Rb. LIN-8 likely acts with the synMuv A proteins LIN-15A and LIN-56 in the nucleus, possibly in a protein complex with the synMuv B protein LIN-35 Rb. Other LIN-8 family members may function in similar complexes in different cells or at different stages. The nuclear localization of LIN-15A, LIN-56, and LIN-8, as well as our observation of a direct physical interaction between class A and class B synMuv proteins, supports the hypothesis that the class A synMuv genes control vulval induction through the transcriptional regulation of gene expression.

Multiple Levels of Redundant Processes InhibitCaenorhabditis elegansVulval Cell Fates

“…Given that lin-8 lin-56 and lin-56; lin-15A double mutants were not enhanced when compared to their respective single mutants, the two genes in each of these gene pairs might act in the same process. Alternatively, they might act in different processes, with the decrease in synMuv gene function in these experiments being insufficient to reach the threshold necessary to cause a Muv phenotype, just as certain synMuv gene double mutants were Muv only if strong loss-of-function alleles were used, e.g., lin-8(n2741); lin-15B(n2245) was 1% Muv at 15°, while lin-8(n2376); lin-15B(n2245) was 98% Muv at 15° (Davison et al 2005). Because the lin-8; lin-15A double mutant had an enhanced vulval phenotype, indicating that lin-8 and lin-15A act in separate processes, one or both of the class A-A synMuv gene pairs lin-8 lin-56 and lin-56; lin-15A must act in parallel.…”

“…We used a partial loss-of-function allele of lin-38, because a null mutation caused larval lethality, which precluded scoring of the vulval phenotype (A. M. Saffer and H. R. Horvitz, unpublished results). Whereas class A single mutants do not have Muv phenotypes at 20° (Ferguson and Horvitz 1989;Thomas et al 2003;Davison et al 2005), some class A synMuv mutations caused very weak Muv phenotypes at 25°, with ,1% penetrance ( Table 2). We also observed the vulval phenotypes of class A-A double mutants (Table 2).…”

“…This synthetic interaction indicates that the class A and class B synMuv genes act in two redundant pathways or processes to inhibit the adoption of vulval cell fates. The class A synMuv genes encode nuclear proteins proposed to regulate transcription (Clark et al 1994;Huang et al 1994;Davison et al 2005). Many class B synMuv genes encode homologs of regulators of transcription and chromatin, including a nucleosome remodeling and deacetylase (NuRD) complex (Solari and Ahringer 2000;Unhavaithaya et al 2002), an Rb/E2F4/DP complex (Lu and Horvitz 1998;Ceol and Horvitz 2001), two histone methyltransferases (Andersen and Horvitz 2007), heterochromatin protein 1 (HP1) (Couteau et al 2002) and the DP/Rb/MuvB (DRM) complex .…”

Identification and Classification of Genes That Act Antagonistically to let-60 Ras Signaling in Caenorhabditis elegans Vulval Development

“…The molecular identities of class B and class C synMuv genes suggest that chromatin remodeling and modification are important in specifying P(3-8).p fates. The class A synMuv genes lin-15A and lin-8 encode novel proteins (Clark et al 1994;Huang et al 1994;Davison et al 2005). Little is known about the mechanism of action of the class A synMuv genes.…”

The LIN-15A and LIN-56 Transcriptional Regulators Interact to Negatively Regulate EGF/Ras Signaling inCaenorhabditis elegansVulval Cell-Fate Determination

“…Hermaphrodites carrying only a single synMuv mutation generally appear as wild type for vulval induction, while hermaphrodites carrying mutations in both a class A and a class B synMuv gene exhibit a Muv phenotype. Four class A synMuv genes and at least 25 class B genes have been identified (Horvitz and Sulston 1980;Horvitz 1985, 1989;Lu and Horvitz 1998;Hsieh et al 1999;Solari and Ahringer 2000;von Zelewsky et al 2000;Horvitz 2001, 2004;Couteau et al 2002;Unhavaithaya et al 2002;Thomas et al 2003;Davison et al 2005;Poulin et al 2005;Harrison et al 2006Harrison et al , 2007Andersen and Horvitz 2007). The synMuv genes likely act upstream of EGF/Ras signaling, as loss-offunction of components of the EGF/Ras pathway can suppress the synMuv phenotype (Ferguson et al 1987;Huang et al 1994;Lu and Horvitz 1998;Horvitz 2001, 2004;Cui et al 2006).…”