Neural expression of hikaru genki protein during embryonic and larval development of Drosophila melanogaster

Hikaru genki (HIG) is a putative secreted protein of Drosophila that belong s to immunoglobulin and complement-binding protein superfamilies. Previous studies reported that, during pupal and adult stages, HIG protein is synthe sized in subsets of neurons and appears to be secreted to the synaptic clef ts of neuron-neuron synapses in the central nervous system (CNS). Here we r eport the analyses of distribution patterns of HIG protein at embryonic and larval stages. In embryos, HIG was mainly observed in subsets of neurons o f the CNS that include pCC interneurons and RP5 motorneurons. At third inst ar larval stage, this protein was detected in a limited number of cells in the brain and ventral nerve cord. Among them are the motorneurons that exte nd their axons to make neuromuscular junctions on body wall muscle 8. Immun oelectron microscopy showed that these axonal processes as well as the neur omuscular terminals contain numerous vesicles with HIG staining, suggesting that HIG is in a pathway of secretion at this stage. Some neurosecretory c ells were also found to express this protein. These data suggest that HIG f unctions in the nervous system through most developmental stages and may se rve as a secreted signalling molecule to modulate the property of synapses or the physiology of the postsynaptic cells.