Cell migrations are an essential part of the development of a multicellular organism. We use the excretory cell of the nematode Caenorhabditis elegans as a model to study both dorso-ventral and antero-posterior migrations. Previous genetic analysis of single and multiple mutants showed that
unc-53,
unc-5 and
unc-71 represent genes of different pathways that interact in the dorsoventral growth cone steering of the excretory canals. Mutations in these three genes strongly enhance each other: whereas in
unc-53(
n152) less than 5% of the animals show ectopic ventral canals and in
unc-71(
e541) and
unc-5(
e53) there are 22% and 35% of them, respectively, we find up to 94% of ventral canals in the triple mutant strain. Based on this enhancement we designed forward genetic screens in the
unc-53 background to find mutants identifying new genes in the other two pathways. Two of the mutants isolated in the genetic screen are new alleles of
unc-71, thus validating the screen. We cloned
unc-71, identified the mutations in several alleles and present the rescue of the excretory canal phenotype of
unc-71 mutants.
unc-71 /
adm-1 is a member of the ADAM family of proteins. Expression of GFP driven by the
unc-71 promotor is consistent with the phenotypes of the mutants. As an alternative approach we performed a Yeast-Two-Hybrid screen for UNC-5 interactors and functionally analyzed the genetic interactions of
unc-53 and
unc-71 with the positives. We focus here primarily on
unc-14 and its direct interactor
unc-51 (Ogura et al., 1997) and on
apr-1. The positions of
unc-14 and
unc-51 in the netrin pathway downstream of
unc-5 were confirmed by analysis of their doubles with
unc-53(
n152) and
unc-71(
e541). Our genetic analysis reveals that the apparently simple dorsalward migration of the excretory canals is in fact a complex decision involving an extended genetic network, composed by partially redundant genes and pathways. The identification of UNC-5 interactors on the other hand gives a first insight in the genes acting in the pathway downstream of this netrin receptor. Ogura,K., Shirakawa, M., Barnes, T.M. , Hekimi, S., Ohshima, Y., Genes Devel., 11(1997), 1801-1811