果蠅高基氏體蛋白質(Rotini)的發育遺傳功能角色探討

Abstract

Rotini, the homologous of human GOLPH3, is a novel Golgi protein found in Drosophila. Based on the phenotypes display by rti GLC embryo, we studied the possible mechanisms of Rti during development. The exostosin (EXT) genes encode glycosyltransferases required for glycosaminoglycan (GAG) chain polymerization in the biosynthesis of heparan sulfate proteoglycans (HSPGs). As a Golgi protein, Rti mediates the retrograde trafficking of the EXTs glycotransferase enzymes within the Golgi. A reduction in Rti shifts the steady-state distribution of EXTs to the trans-Golgi. These accumulated EXTs tend to be degraded and their re-entrance towards the route for polymerizing GAG chains is disengaged. Conversely, EXTs are mislocalized towards the ER/cis-Golgi when Rti is over-expressed. Both loss of function and overexpression of rti result in incomplete HSPGs and perturb Hedgehog (Hh) signaling. This model is consistent with a role of GOLPH3 in human bone and cartilage cells, whereby GOLPH3 modulates the dynamic retention and protein stability of EXT1/2. Mutation in the tumor suppressor genes EXT1 and EXT2 disturb HSPG biosynthesis and cause multiple osteochondromas (MO). Our data demonstrate that GOLPH3 affects the sub-compartmental distribution of EXT1 and 2 in the Golgi, providing a putative function of GOLPH3 in MO etiology. To study the role of Rti in dorsoventral patterning formation in Drosophila embryo, we focused on three serine proteases, Gastrulation Defective (GD), Snake (Snk), and Easter (Ea). In rti GLC embryos, the protein levels of zymogens form of the three proteases significantly increased, but the processed/cleavage forms are barely detectable. When rti is mutated, the prematurely cleaved Snk has already existed in ovary. These suggest that Rti may affect protein level and cleavage processing of three serine proteases. In summary, Rti/GOLPH3 regulates the retrograde trafficking of EXTs to modulate the dynamic retention of EXTs within the Golgi. An effect of EXTs by GOLPH3 provides a putative role for GOLPH3 in the formation of MO. Besides, Rti affects GD, Snk, and Ea serine proteases to determine the dorsoventral patterning in the Drosophila embryo.