Locomotion defects, together with Pins, regulates heterotrimeric G-protein signaling during Drosophila neuroblast asymmetric divisions

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Abstract
Heterotrimeric G proteins mediate asymmetric division of Drosophila neuroblasts. Free Gβγ appears to be crucial for the generation of an asymmetric mitotic spindle and consequently daughter cells of distinct size. However, how Gβγ is released from the inactive heterotrimer remains unclear. Here we show that Locomotion defects (Loco) interacts and colocalizes with Gαi and, through its GoLoco motif, acts as a guanine nucleotide dissociation inhibitor (GDI) for Gαi. Simultaneous removal of the two GoLoco motif proteins, Loco and Pins, results in defects that are essentially indistinguishable from those observed in Gβ13F or Gγ1 mutants, suggesting that Loco and Pins act synergistically to release free Gβγ in neuroblasts. Furthermore, the RGS domain of Loco can also accelerate the GTPase activity of Gαi to regulate the equilibrium between the GDP- and the GTP-bound forms of Gαi. Thus, Loco can potentially regulate heterotrimeric G-protein signaling via two distinct modes of action during Drosophila neuroblast asymmetric divisions.