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Cloning of a Rab3 isotype predominantly expressed in adipocytes.

ABSTRACT: We have isolated the cDNA for Rab3D, an additional member of the small molecular weight GTP-binding protein family. Rab3D message is abundant in mouse adipocytes. It is increased during differentiation of 3T3-L1 cells into adipocytes, temporally coincident with the appearance of the insulin-sensitive glucose transporter GLUT4. Rab3D is a close homolog of Rab3A, which is found on the cytoplasmic surface of neurosecretory vesicles and which may be involved in their regulated secretion. Since our previous work showed that in permeabilized adipocytes nonhydrolizable GTP analogs mimic insulin in triggering exocytosis of GLUT4-containing vesicles, Rab3D may be involved in the insulin-induced exocytosis of GLUT4-containing vesicles in adipocytes.

SUBMITTER: Baldini G

PROVIDER: S-EPMC49226 | biostudies-other | 1992 Jun

REPOSITORIES: biostudies-other

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Cloning of a Rab3 isotype predominantly expressed in adipocytes.

Baldini G G Hohl T T Lin H Y HY Lodish H F HF

Proceedings of the National Academy of Sciences of the United States of America 19920601 11

We have isolated the cDNA for Rab3D, an additional member of the small molecular weight GTP-binding protein family. Rab3D message is abundant in mouse adipocytes. It is increased during differentiation of 3T3-L1 cells into adipocytes, temporally coincident with the appearance of the insulin-sensitive glucose transporter GLUT4. Rab3D is a close homolog of Rab3A, which is found on the cytoplasmic surface of neurosecretory vesicles and which may be involved in their regulated secretion. Since our p ...[more]

PMID: 1594612

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Project description:BACKGROUND: Sterile alpha motif (SAM) domains are approximately 70 residues long and have been reported as common protein-protein interaction modules. This domain is found in a large number of proteins, including Polycomb group (PcG) proteins and ETS family transcription factors. In this work, we report the cloning and functional characterization of a novel SAM domain-containing protein, which is predominantly expressed in retinal photoreceptors and the pineal gland and is designated mouse mr-s (major retinal SAM domain protein). RESULTS: mr-s is evolutionarily conserved from zebrafish through human, organisms through which the mechanism of photoreceptor development is also highly conserved. Phylogenetic analysis suggests that the SAM domain of mr-s is most closely related to a mouse polyhomeotic (ph) ortholog, Mph1/Rae28, which is known as an epigenetic molecule involved in chromatin modifications. These findings provide the possibility that mr-s may play a critical role by regulating gene expression in photoreceptor development. mr-s is preferentially expressed in the photoreceptors at postnatal day 3-6 (P3-6), when photoreceptors undergo terminal differentiation, and in the adult pineal gland. Transcription of mr-s is directly regulated by the cone-rod homeodomain protein Crx. Immunoprecipitation assay showed that the mr-s protein self-associates mainly through the SAM domain-containing region as well as ph. The mr-s protein localizes mainly in the nucleus, when mr-s is overexpressed in HEK293T cells. Moreover, in the luciferase assays, we found that mr-s protein fused to GAL4 DNA-binding domain functions as a transcriptional repressor. We revealed that the repression activity of mr-s is not due to a homophilic interaction through its SAM domain but to the C-terminal region. CONCLUSION: We identified a novel gene, mr-s, which is predominantly expressed in retinal photoreceptors and pineal gland. Based on its expression pattern and biochemical analysis, we predict that mr-s may function as a transcriptional repressor in photoreceptor cells and in pinealocytes of the pineal gland.

Project description:BackgroundIn fish, molecular mechanisms that control follicle-enclosed oocyte progression throughout oogenesis and oocyte developmental competence acquisition remain poorly understood. Existing data in mammals have indicated that the so called "oocyte-specific" genes play an important role in oogenesis, fertilization, and early embryo development. In teleost species, very little is known about "oocyte-specific" genes. The present study therefore aimed at identifying and characterizing oocyte-specific genes in fish.ResultsUsing digital differential display PCR, mouse ESTs exhibiting an oocyte-predominant expression were identified. Those murine ESTs were subsequently used to identify cognate rainbow trout (Oncorhynchus mykiss) ESTs using a reciprocal Blast search strategy. In the present study we report the identification of five previously uncharacterized rainbow trout cDNAs exhibiting a oocyte-specific, oocyte-predominant, or gonad-specific expression: zygote arrest 1 (zar1), v-mos Moloney murine sarcoma viral oncogene-like protein (mos), B-cell translocation gene (btg3), growth differentiation factor 9 (gdf9), and mutS homolog 4 (msh4). The orthology relationship of each of these genes with vertebrate counterparts was verified by phylogenetic analysis. Among those five genes, three had never been characterized in any fish species. In addition, we report the oocyte-predominant expression of btg3 for the first time in any vertebrate species. Finally, those five genes are present in unfertilized eggs as maternally-inherited mRNAs thus suggesting that they could participate in ovarian folliculogenesis as well as early embryonic development.ConclusionThe expression patterns of zar1, mos, btg3, gdf9 and msh4 in rainbow trout and the functions of their orthologs in higher vertebrates strongly suggest that they might play an important role in follicle-enclosed oocyte development, meiosis control and early embryonic development in fish. Future investigations are however required to unravel the participation of those strong candidates in the molecular processes that control folliculogenesis and/or oocyte developmental competence in fish.

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Cloning of a Rab3 isotype predominantly expressed in adipocytes.

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Cloning of a Rab3 isotype predominantly expressed in adipocytes.

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