Abstract
Genetic screens in the nematode Caenorhabditis elegans identified the EGF/Ras and Notch pathways as central for vulval precursor cell fate patterning. Schematically, the anchor cell secretes EGF, inducing the P6.p cell to a primary (1°) vulval fate; P6.p in turn induces its neighbors to a secondary (2°) fate through Delta-Notch signaling and represses Ras signaling. In the nematode Oscheius tipulae, the anchor cell successively induces 2° then 1° vulval fates. Here, we report on the molecular identification of mutations affecting vulval induction in O. tipulae A single Induction Vulvaless mutation was found, which we identify as a cis-regulatory deletion in a tissue-specific enhancer of the O. tipulae lin-3 homolog, confirmed by clustered regularly interspaced short palindromic repeats/Cas9 mutation. In contrast to this predictable Vulvaless mutation, mutations resulting in an excess of 2° fates unexpectedly correspond to the plexin/semaphorin pathway. Hyperinduction of P4.p and P8.p in these mutants likely results from mispositioning of these cells due to a lack of contact inhibition. The third signaling pathway found by forward genetics in O. tipulae is the Wnt pathway; a decrease in Wnt pathway activity results in loss of vulval precursor competence and induction, and 1° fate miscentering on P5.p. Our results suggest that the EGF and Wnt pathways have qualitatively similar activities in vulval induction in C. elegans and O. tipulae, albeit with quantitative differences in the effects of mutation. Thus, the derived induction process in C. elegans with an early induction of the 1° fate appeared during evolution, after the recruitment of the EGF pathway for vulval induction.
Highlights
Genetic screens in the nematode Caenorhabditis elegans identified the EGF/Ras and Notch pathways as central for vulval precursor cell fate patterning
The Oti-lin-3 mRNA level in the anchor cell was much decreased in animals bearing the Oti-lin-3(mf86) deletion compared to animals of the CEW1 reference strain (Figure 2C, Kolmogorov–Smirnov test, P, 10214), while Oti-lin-3 expression elsewhere in the pharynx and in the germline was retained (Figure S7B), as in the C. elegans cis-regulatory mutant lin-3(e1417) (Saffer et al 2011)
The O. tipulae genome contains five genes coding for Wnt signaling molecules, which we found to be 1:1 orthologs to the five Wnt genes in C. elegans (Figure S4)
Summary
Genetic screens in the nematode Caenorhabditis elegans identified the EGF/Ras and Notch pathways as central for vulval precursor cell fate patterning. A single Induction Vulvaless mutation was found, which we identify as a cisregulatory deletion in a tissue-specific enhancer of the O. tipulae lin-3 homolog, confirmed by clustered regularly interspaced short palindromic repeats/Cas mutation In contrast to this predictable Vulvaless mutation, mutations resulting in an excess of 2° fates unexpectedly correspond to the plexin/semaphorin pathway. The C. elegans Induction Vulvaless and Multivulva mutants allowed the identification of the EGF/Ras/MAP kinase pathway, the former class corresponding to a loss of activity in the pathway and the latter to a gain of activity (Sternberg 2005). Studies of the interplay between the EGF and Delta/Notch pathways in the patterning vulval cell fates have established this system as a textbook example of intercellular signaling and organogenesis (Sternberg and Han 1998)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
