Visualization of cleavage furrow proteins in fixed dividing spermatocytes

Identification of GOLPH3 Partners in Drosophila Unveils Potential Novel Roles in Tumorigenesis and Neural Disorders

Golgi phosphoprotein 3 (GOLPH3) is a highly conserved peripheral membrane protein localized to the Golgi apparatus and the cytosol. GOLPH3 binding to Golgi membranes depends on phosphatidylinositol 4-phosphate [PI(4)P] and regulates Golgi architecture and vesicle trafficking. GOLPH3 overexpression has been correlated with poor prognosis in several cancers, but the molecular mechanisms that link GOLPH3 to malignant transformation are poorly understood. We recently showed that PI(4)P-GOLPH3 couples membrane trafficking with contractile ring assembly during cytokinesis in dividing Drosophila spermatocytes. Here, we use affinity purification coupled with mass spectrometry (AP-MS) to identify the protein-protein interaction network (interactome) of Drosophila GOLPH3 in testes. Analysis of the GOLPH3 interactome revealed enrichment for proteins involved in vesicle-mediated trafficking, cell proliferation and cytoskeleton dynamics. In particular, we found that dGOLPH3 interacts with the Drosophila orthologs of Fragile X mental retardation protein and Ataxin-2, suggesting a potential role in the pathophysiology of disorders of the nervous system. Our findings suggest novel molecular targets associated with GOLPH3 that might be relevant for therapeutic intervention in cancers and other human diseases.

A novel coordinated function of Myosin II with GOLPH3 controls centralspindlin localization during cytokinesis in Drosophila

In animal cell cytokinesis, interaction of non-muscle myosin II (NMII) with F-actin provides the dominant force for pinching the mother cell into two daughters. Here we demonstrate that celibe (cbe) is a missense allele of zipper, which encodes the Drosophila Myosin heavy chain. Mutation of cbe impairs binding of Zipper protein to the regulatory light chain Spaghetti squash (Sqh). In dividing spermatocytes from cbe males, Sqh fails to concentrate at the equatorial cortex, resulting in thin actomyosin rings that are unable to constrict. We show that cbe mutation impairs localization of the phosphatidylinositol 4-phosphate [PI(4)P]-binding protein Golgi phosphoprotein 3 (GOLPH3, also known as Sauron) and maintenance of centralspindlin at the cell equator of telophase cells. Our results further demonstrate that GOLPH3 protein associates with Sqh and directly binds the centralspindlin subunit Pavarotti. We propose that during cytokinesis, the reciprocal dependence between Myosin and PI(4)P-GOLPH3 regulates centralspindlin stabilization at the invaginating plasma membrane and contractile ring assembly.

Drosophila Doublefault protein coordinates multiple events during male meiosis by controlling mRNA translation

During the extended prophase of Drosophila gametogenesis, spermatocytes undergo robust gene transcription and store many transcripts in the cytoplasm in a repressed state, until translational activation of select mRNAs in later steps of spermatogenesis. Here, we characterize the Drosophila Doublefault (Dbf) protein as a C2H2 zinc-finger protein, primarily expressed in testes, that is required for normal meiotic division and spermiogenesis. Loss of Dbf causes premature centriole disengagement and affects spindle structure, chromosome segregation and cytokinesis. We show that Dbf interacts with the RNA-binding protein Syncrip/hnRNPQ, a key regulator of localized translation in Drosophila We propose that the pleiotropic effects of dbf loss-of-function mutants are associated with the requirement of dbf function for translation of specific transcripts in spermatocytes. In agreement with this hypothesis, Dbf protein binds cyclin B mRNA and is essential for translation of cyclin B in mature spermatocytes.

[Impact of GOLPH3 expression in cumulus granulosa cells on outcomes of intracytoplasmic sperm injection]

OBJECTIVE

To evaluate the impact of GOLPH3 expression in cumulus granulosa cells on the outcomes of intracytoplasmic sperm injection (ICSI).

METHODS

A total of 119 women receiving ICSI due to male infertility at our center between April, 2012 and June, 2014 were enrolled in the study. Cumulus granulosa cells were collected from the women for detection of GOLPH3 expressions using immunocytochemistry, Western blotting, and real-time PCR. GOLPH3 expression rate was compared between women with and without clinical pregnancy following ICSI, and the associations of GOLPH3 expression with the laboratory indicators of ICSI outcomes were assessed.

RESULTS

Immunocytochemistry showed that GOLPH3 expression was located mainly in in the plasma of the cumulus granulosa cells. The rate and intensity of GOLPH3 expression in the cumulus granulosa cells differed significantly between women with and without clinical pregnancy following ICSI (P<0.05). GOLPH3 expression was found to positively correlate with the numbers of punctured follicles, grade III oocyte cumulus complex, ICSI oocytes, fertilized oocytes, cleavage, high quality embryos, blastocysts, high quality blastocysts, and frozen embryos (all P<0.01). The results of RTPCR and Western blotting revealed significant differences in GOLPH3 expressions at both the mRNA and protein levels in the cumulus granulosa cells between the pregnant and non-pregnant groups after ICSI (t=14.560, P=0.000). Western blot analysis revealed significant difference of GOLPH3 protein expression in cumulus granulosa cells between women with and without clinical pregnancy following ICSI.

CONCLUSION

GOLPH3 expression in the cumulus granulosa cells plays an important role in the development of oocytes and promotion of conception to affect the outcomes of ICSI.

COG7 deficiency in Drosophila generates multifaceted developmental, behavioral and protein glycosylation phenotypes

Congenital disorders of glycosylation (CDG) comprise a family of human multisystemic diseases caused by recessive mutations in genes required for protein N-glycosylation. More than 100 distinct forms of CDGs have been identified and most of them cause severe neurological impairment. The Conserved Oligomeric Golgi (COG) complex mediates tethering of vesicles carrying glycosylation enzymes across the Golgi cisternae. Mutations affecting human COG1, COG2 and COG4-COG8 cause monogenic forms of inherited, autosomal recessive CDGs. We have generated a Drosophila COG7-CDG model that closely parallels the pathological characteristics of COG7-CDG patients, including pronounced neuromotor defects associated with altered N-glycome profiles. Consistent with these alterations, larval neuromuscular junctions of Cog7 mutants exhibit a significant reduction in bouton numbers. We demonstrate that the COG complex cooperates with Rab1 and Golgi phosphoprotein 3 to regulate Golgi trafficking and that overexpression of Rab1 can rescue the cytokinesis and locomotor defects associated with loss of Cog7. Our results suggest that the Drosophila COG7-CDG model can be used to test novel potential therapeutic strategies by modulating trafficking pathways.

Rab1 interacts with GOLPH3 and controls Golgi structure and contractile ring constriction during cytokinesis in Drosophila melanogaster

Cytokinesis requires a tight coordination between actomyosin ring constriction and new membrane addition along the ingressing cleavage furrow. However, the molecular mechanisms underlying vesicle trafficking to the equatorial site and how this process is coupled with the dynamics of the contractile apparatus are poorly defined. Here we provide evidence for the requirement of Rab1 during cleavage furrow ingression in cytokinesis. We demonstrate that the gene omelette (omt) encodes the Drosophila orthologue of human Rab1 and is required for successful cytokinesis in both mitotic and meiotic dividing cells of Drosophila melanogaster We show that Rab1 protein colocalizes with the conserved oligomeric Golgi (COG) complex Cog7 subunit and the phosphatidylinositol 4-phosphate effector GOLPH3 at the Golgi stacks. Analysis by transmission electron microscopy and 3D-SIM super-resolution microscopy reveals loss of normal Golgi architecture in omt mutant spermatocytes indicating a role for Rab1 in Golgi formation. In dividing cells, Rab1 enables stabilization and contraction of actomyosin rings. We further demonstrate that GTP-bound Rab1 directly interacts with GOLPH3 and controls its localization at the Golgi and at the cleavage site. We propose that Rab1, by associating with GOLPH3, controls membrane trafficking and contractile ring constriction during cytokinesis.