Transcriptional regulator within D-type neurons that controls terminal differentiation (PubMed:7997265). Required for the development and function of the 19 inhibitory GABAergic (gamma-aminobutyric-acid-secreting) D-type motor neurons, which control locomotion (PubMed:7997265). Plays a role in regulating synapse formation in dorsal D (DD) and ventral D (VD) GABAergic motor neurons, possibly in part by regulating the expression of the neural regulator oig-1 (PubMed:26083757). Also required for expression of flp-13 in DD motor neurons (PubMed:15882588). Plays a role in respecification of DD motor neurons through regulation of genes involved in the modulation of cellular cAMP including pde-4 which hydrolyzes cAMP and acy-1 which catalyzes cAMP formation (PubMed:29033363). Expressed in D-type GABAergic motor neurons at high levels in young larvae, in which the motor circuitry is formed, and at low levels in older animals (PubMed:7997265). Also present in six non-GABAergic motor neurons and is absent from the seven non-D-type GABAergic neurons (PubMed:7997265). Expressed in DD GABAergic motor neurons and VD GABAergic motor neurons (PubMed:15882588, PubMed:26083757, PubMed:29033363). Aberrant synaptic connectivity of dorsal and ventral D-type motor neurons onto ventral and dorsal muscle. Belongs to the paired homeobox family. Bicoid subfamily.