Acts in the nervous system to mediate the control of copulatory organs during courtship. Found in the cytoplasm of many neuronal and glial cells in the brain and ventral ganglion, and in imaginal disks. At stage 11, expression is restricted to the neuroblasts, predominant in the central nervous system (CNS), including the brain and ventral nerve cord, and in the PNS. Later embryonic expression is seen in the gonads. Late third instar larvae show expression in the CNS, imaginal disks (including genital, eye-antennal, leg, wing and haltere disks), and gonads. In the larval brain, it is expressed in all of the glial cells and in clusters of neurons that projected contralaterally. In the larval ventral ganglion, it is expressed in subperineurial glia, peripheral exit glia, and a number of interneurons, but not in motor neurons. Isoform B is abundantly expressed in males and females. Isoform D is male specific and expressed at low levels. Expressed both maternally and zygotically throughout development. Zygotic expression levels rise after embryonic stage 9. Male flies exhibit abnormal copulation. They fail to successfully withdraw their genitalia upon termination of copulation so end up 'stuck' to the female, tugging to separate. There is also a 'non-copulating' behavioral phenotype. There are no morphological defects in the male genitalia. Females can mate successfully but have reduced fertility. Complete loss of lig function results in lethality during early pupal stages.