C-elegans slit acts in midline, dorsal-ventral, and anterior-posterior guidance via the SAX-3/Robo receptor

Robo receptors interact with ligands of the Slit family. The nematode C. el egans has one Robo receptor (SAX-3) and one Slit protein (SLT-1), which dir ect ventral axon guidance and guidance at the midline. In larvae, slt-1 exp ression in dorsal muscles repels axons to promote ventral guidance. SLT-1 a cts through the SAX-3 receptor, in parallel with the ventral attractant UNC -6 (Netrin). Removing both UNC-6 and SLT-1 eliminates all ventral guidance information for some axons, revealing an underlying longitudinal guidance p athway. In the embryo, slt-1 is expressed at high levels in anterior epider mis. Embryonic expression of SLT-1 provides anterior-posterior guidance inf ormation to migrating CAN neurons. Surprisingly, slt-1 mutants do not exhib it the nerve ring and epithelial defects of sax-3 mutants, suggesting that SAX-3 has both Slit-dependent and Slit-independent functions in development .