Mutations in Caenorhabditis briggsae identify new genes important for limiting the response to EGF signaling during vulval development

Abstract

Studies of vulval development in the nematode C. elegans have identified many genes that are involved in cell division and differentiation processes. Some of these encode components of conserved signal transduction pathways mediated by EGF, Notch, and Wnt. To understand how developmental mechanisms change during evolution, we are doing a comparative analysis of vulva formation in C. briggsae, a species that is closely related to C. elegans. Here, we report 14 mutations in 7 Multivulva (Muv) genes in C. briggsae that inhibit inappropriate division of vulval precursors. We have developed a new efficient and cost-effective gene mapping method to localize Muv mutations to small genetic intervals on chromosomes, thus facilitating cloning and functional studies. We demonstrate the utility of our method by determining molecular identities of three of the Muv genes that include orthologs of Cel-lin-1 (ETS) and Cel-lin-31 (Winged-Helix) of the EGF-Ras pathway and Cel-pry-1 (Axin), of the Wnt pathway. The remaining four genes reside in regions that lack orthologs of known C. elegans Muv genes. Inhibitor studies demonstrate that the Muv phenotype of all four new genes is dependent on the activity of the EGF pathway kinase, MEK. One of these, Cbr-lin(gu167), shows modest increase in the expression of Cbr-lin-3/EGF compared to wild type. These results argue that while Cbr-lin(gu167) may act upstream of Cbr-lin-3/EGF, the other three genes influence the EGF pathway downstream or in parallel to Cbr-lin-3. Overall, our findings demonstrate that the genetic program underlying a conserved developmental process includes both conserved and divergent functional contributions.

From “the Worm” to “the Worms” and Back Again: The Evolutionary Developmental Biology of Nematodes

“…Nevertheless, the LIN-12 /Notch pathway is still involved in lateral inhibition in C. briggsae and LIN-3 /EGF acts in a dose-dependent manner on VPC fate specification ( Félix 2007 ). However, inactivation of genes of the vulva specification pathways in C. elegans and C. briggsae often leads to different phenotypes, revealing a difference in the respective contributions of these pathways ( Rudel and Kimble 2001 ; Sharanya et al 2012 , 2015 ; Mahalak et al 2017 ). Thus, evolutionary changes in the patterning of the vulva are not necessarily due to rewiring of the signaling pathways, but can also be attributed to quantitative changes of the same network of signaling pathways ( Haag and True 2007 ).…”

“…Alternatively, higher pleiotropy of the genes involved in vulval patterning in O. tipulae could lead to embryonic death or sterility, thus preventing the detection of specific classes of mutants ( Dichtel et al 2001 ; Louvet-Vallee et al 2003 ; Dichtel-Danjoy and Félix 2004a ). Similarly, screens in C. briggsae ( Sharanya et al 2012 , 2015 ) failed to identify mutants lacking VPC induction, and mapping of mutants indicates there are novel players relative to the C. elegans paradigm.…”

Integration of EGFR and LIN-12/Notch Signaling by LIN-1/Elk1, the Cdk8 Kinase Module, and SUR-2/Med23 in Vulval Precursor Cell Fate Patterning in Caenorhabditis elegans

“…We note that there are differences in the contributions of the EGFR-Ras-ERK pathway to vulval development in other species when compared to C. elegans (Felix 2007;Sommer 2012). There also may be differences in the contributions of the components we have studied here to vulval development in the related species C. briggsae; the ortholog of lin-1 is critical for inhibiting ectopic vulval fate (Sharanya et al 2015), but the ortholog of sur-2 may not be essential for production of the lateral signal (Mahalak et al 2017). Finally, these components function in different configurations and activate or repress different target genes in other developmental contexts in C. elegans, such the excretory system (Howard and Sundaram 2002;Rocheleau et al 2002;Sundaram and Buechner 2016).…”

Toward Universal Forward Genetics: Using a Draft Genome Sequence of the NematodeOscheius tipulaeTo Identify Mutations Affecting Vulva Development

“…High-quality genome assemblies have been generated for C. briggsae ( Stein et al 2003 ) and P. pacificus ( Dieterich et al 2008 ). Classical techniques have been employed to map and identify genes involved in different traits with particular emphasis on the convergent evolution of self-fertile hermaphroditism, reviewed in Ellis and Lin (2014) , and vulva development ( Seetharaman et al 2010 ; Sharanya et al 2012 , 2015 ; Sommer 2012 ; Kienle and Sommer 2013 ). In P. pacificus , genetic analyses of the evolution of sex muscles ( Photos et al 2006 ), gonad development ( Rudel et al 2008 ), dauer formation ( Ogawa et al 2009 , 2011 ), and buccal tooth dimorphism ( Bento et al 2010 ) have been published.…”