Mechanisms controlling sex myoblast migration in Caenorhabditis elegans hermaphrodites

Sex myoblast migration in C. elegans hermaphrodites is controlled by multip le guidance mechanisms. A gonad-dependent attraction functions to guide the sex myoblasts to their precise final positions flanking the gonad. In the absence of this attraction, a gonad-dependent repulsion is revealed. In add ition to gonad-dependent influences, a gonad-independent mechanism propels the sex myoblasts anteriorly to a broad range of positions near the center of the animal. Here we describe a temporal analysis of sex myoblast migrati on that reveals when the gonad-dependent attraction and the gonad-independe nt mechanisms normally function. We provide evidence that EGL-17, a fibrobl ast growth factor-like protein, is expressed in the gonadal cells required to attract the sex myoblasts to their precise final positions, further supp orting our model that EGL-17 defines the gonad-dependent attractant. Furthe rmore, cell ablation experiments reveal that EGL-17 and the gonad-dependent repellent likely emanate from the same cellular sources. Analyses of candi date mutations for their effects on the gonad-dependent repulsion reveal th at a set of genes known to affect multiple aspects of axonogenesis, unc-14, unc-33, unc-44, and unc-51, is essential for this repulsive mechanism. In addition, we have discovered that a SAX-3/Roundabout-dependent mechanism is used to maintain the sex myoblasts along the ventral muscle quadrants. (C) 2000 Academic Press.