Fig. 7. Specification of DA versus DB motoneurones fate. UNC-4 blocks expression of DB genes in DA motoneurones. It is not known if UNC-4 also acts to promote expression of DA-specific genes. VAB-7 specifies DB traits (posterior axonal polarity, acr-5 expression) by repressing UNC-4 and by acting in a parallel UNC-4-independent pathway. The posterior trajectory of DB motoneurones may also depend on another unknown pathway (?) that does not involve VAB-7. Nerve cord fasciculation is uniquely dependent on VAB-7 function.
