Mrj encodes a DnaJ-related co-chaperone that is essential for murine placental development. (1/7966)

We have identified a novel gene in a gene trap screen that encodes a protein related to the DnaJ co-chaperone in E. coli. The gene, named Mrj (mammalian relative of DnaJ) was expressed throughout development in both the embryo and placenta. Within the placenta, expression was particularly high in trophoblast giant cells but moderate levels were also observed in trophoblast cells of the chorion at embryonic day 8.5, and later in the labyrinth which arises from the attachment of the chorion to the allantois (a process called chorioallantoic fusion). Insertion of the ROSAbetageo gene trap vector into the Mrj gene created a null allele. Homozygous Mrj mutants died at mid-gestation due to a failure of chorioallantoic fusion at embryonic day 8.5, which precluded formation of the mature placenta. At embryonic day 8.5, the chorion in mutants was morphologically normal and expressed the cell adhesion molecule beta4 integrin that is known to be required for chorioallantoic fusion. However, expression of the chorionic trophoblast-specific transcription factor genes Err2 and Gcm1 was significantly reduced. The mutants showed no abnormal phenotypes in other trophoblast cell types or in the embryo proper. This study indicates a previously unsuspected role for chaperone proteins in placental development and represents the first genetic analysis of DnaJ-related protein function in higher eukaryotes. Based on a survey of EST databases representing different mouse tissues and embryonic stages, there are 40 or more DnaJ-related genes in mammals. In addition to Mrj, at least two of these genes are also expressed in the developing mouse placenta. The specificity of the developmental defect in Mrj mutants suggests that each of these genes may have unique tissue and cellular activities.  (+info)

Identification and characterization of the human orthologue of yeast Pex14p. (2/7966)

Pex14p is a central component of the peroxisomal protein import machinery, which has been suggested to provide the point of convergence for PTS1- and PTS2-dependent protein import in yeast cells. Here we describe the identification of a human peroxisome-associated protein (HsPex14p) which shows significant similarity to the yeast Pex14p. HsPex14p is a carbonate-resistant peroxisomal membrane protein with its C terminus exposed to the cytosol. The N terminus of the protein is not accessible to exogenously added antibodies or protease and thus might protrude into the peroxisomal lumen. HsPex14p overexpression leads to the decoration of tubular structures and mislocalization of peroxisomal catalase to the cytosol. HsPex14p binds the cytosolic receptor for the peroxisomal targeting signal 1 (PTS1), a result consistent with a function as a membrane receptor in peroxisomal protein import. Homo-oligomerization of HsPex14p or interaction of the protein with the PTS2-receptor or HsPex13p was not observed. This distinguishes the human Pex14p from its counterpart in yeast cells and thus supports recent data suggesting that not all aspects of peroxisomal protein import are conserved between yeasts and humans. The role of HsPex14p in mammalian peroxisome biogenesis makes HsPEX14 a candidate PBD gene for being responsible for an unrecognized complementation group of human peroxisome biogenesis disorders.  (+info)

DEF-1, a novel Src SH3 binding protein that promotes adipogenesis in fibroblastic cell lines. (3/7966)

The Src homology 3 (SH3) motif is found in numerous signal transduction proteins involved in cellular growth and differentiation. We have purified and cloned a novel protein, DEF-1 (differentiation-enhancing factor), from bovine brain by using a Src SH3 affinity column. Ectopic expression of DEF-1 in fibroblasts resulted in the differentiation of a significant fraction of the culture into adipocytes. This phenotype appears to be related to the induction of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), since DEF-1 NIH 3T3 cells demonstrated augmented levels of PPARgamma mRNA and, when treated with activating PPARgamma ligands, efficient induction of differentiation. Further evidence for a role for DEF-1 in adipogenesis was provided by heightened expression of DEF-1 mRNA in adipose tissue isolated from obese and diabetes mice compared to that in tissue isolated from wild-type mice. However, DEF-1 mRNA was detected in multiple tissues, suggesting that the signal transduction pathway(s) in which DEF-1 is involved is not limited to adipogenesis. These results suggest that DEF-1 is an important component of a signal transduction process that is involved in the differentiation of fibroblasts and possibly of other types of cells.  (+info)

The nuclear receptor superfamily has undergone extensive proliferation and diversification in nematodes. (4/7966)

The nuclear receptor (NR) superfamily is the most abundant class of transcriptional regulators encoded in the Caenorhabditis elegans genome, with >200 predicted genes revealed by the screens and analysis of genomic sequence reported here. This is the largest number of NR genes yet described from a single species, although our analysis of available genomic sequence from the related nematode Caenorhabditis briggsae indicates that it also has a large number. Existing data demonstrate expression for 25% of the C. elegans NR sequences. Sequence conservation and statistical arguments suggest that the majority represent functional genes. An analysis of these genes based on the DNA-binding domain motif revealed that several NR classes conserved in both vertebrates and insects are also represented among the nematode genes, consistent with the existence of ancient NR classes shared among most, and perhaps all, metazoans. Most of the nematode NR sequences, however, are distinct from those currently known in other phyla, and reveal a previously unobserved diversity within the NR superfamily. In C. elegans, extensive proliferation and diversification of NR sequences have occurred on chromosome V, accounting for > 50% of the predicted NR genes.  (+info)

Molecular and evolutionary analysis of Borrelia burgdorferi 297 circular plasmid-encoded lipoproteins with OspE- and OspF-like leader peptides. (5/7966)

We previously described two OspE and three OspF homologs in Borrelia burgdorferi 297 (D. R. Akins, S. F. Porcella, T. G. Popova, D. Shevchenko, S. I. Baker, M. Li, M. V. Norgard, and J. D. Radolf, Mol. Microbiol. 18:507-520, 1995; D. R. Akins, K. W. Bourell, M. J. Caimano, M. V. Norgard, and J. D. Radolf, J. Clin. Investig. 101:2240-2250, 1998). In this study, we characterized four additional lipoproteins with OspE/F-like leader peptides (Elps) and demonstrated that all are encoded on plasmids homologous to cp32 and cp18 from the B31 and N40 strains, respectively. Statistical analysis of sequence similarities using the binary comparison algorithm revealed that the nine lipoproteins from strain 297, as well as the OspE, OspF, and Erp proteins from the N40 and B31 strains, fall into three distinct families. Based upon the observation that these lipoproteins all contain highly conserved leader peptides, we now propose that the ancestors of each of the three families arose from gene fusion events which joined a common N terminus to unrelated proteins. Additionally, further sequence analysis of the strain 297 circular plasmids revealed that rearrangements appear to have played an important role in generating sequence diversity among the members of these three families and that recombinational events in the downstream flanking regions appear to have occurred independently of those within the lipoprotein-encoding genes. The association of hypervariable regions with genes which are differentially expressed and/or subject to immunological pressures suggests that the Lyme disease spirochete has exploited recombinatorial processes to foster its parasitic strategy and enhance its immunoevasiveness.  (+info)

Hormonal regulation of messenger ribonucleic acid expression for steroidogenic factor-1, steroidogenic acute regulatory protein, and cytochrome P450 side-chain cleavage in bovine luteal cells. (6/7966)

To examine hormonal regulation of genes pertinent to luteal steroidogenesis, bovine theca and granulosa cells derived from preovulatory follicles were cultured with various combinations of forskolin and insulin. On Day 8 of culture, progesterone production was measured, and mRNA levels of steroidogenic factor-1 (SF-1), cytochrome P450 side-chain cleavage enzyme (P450scc), and steroidogenic acute regulatory protein (StAR) were determined by means of semiquantitative reverse transcription-polymerase chain reaction. Notably, the combination of forskolin plus insulin stimulated progesterone production in luteinized theca cells. This was probably a result of a synergistic interaction between forskolin and insulin, observed on both StAR and P450scc mRNA levels. However, in luteinized granulosa cells (LGC), forskolin and insulin each independently were able to up-regulate the levels of P450scc and StAR mRNA levels, respectively. Moreover, insulin alone was sufficient to maintain the high steady-state levels of StAR mRNA in LGC. Both insulin and insulin-like growth factor I enhanced StAR gene expression in LGC. SF-1 was constitutively expressed in bovine luteal cells; its amounts did not vary between the two luteal cell types or with hormonal treatments. In summary, this study demonstrates a distinct, cell-type specific regulation of StAR and P450scc mRNA in the two bovine luteal cell types.  (+info)

Recombinant human peroxisomal targeting signal receptor PEX5. Structural basis for interaction of PEX5 with PEX14. (7/7966)

Import of matrix proteins into peroxisomes requires two targeting signal-specific import receptors, Pex5p and Pex7p, and their binding partners at the peroxisomal membrane, Pex13p and Pex14p. Several constructs of human PEX5 have been overexpressed and purified by affinity chromatography in order to determine functionally important interactions and provide initial structural information. Sizing chromatography and electron microscopy suggest that the two isoforms of the human PTS1 receptor, PEX5L and PEX5S, form homotetramers. Surface plasmon resonance analysis indicates that PEX5 binds to the N-terminal fragment of PEX14-(1-78) with a very high affinity in the low nanomolar range. Stable complexes between recombinant PEX14-(1-78) and both the full-length and truncated versions of PEX5 were formed in vitro. Analysis of these complexes revealed that PEX5 possesses multiple binding sites for PEX14, which appear to be distributed throughout its N-terminal half. Coincidentally, this part of the molecule is also responsible for oligomerization, whereas the C-terminal half with its seven tetratricopeptide repeats has been reported to bind PTS1-proteins. A pentapeptide motif that is reiterated seven times in PEX5 is proposed as a determinant for the interaction with PEX14.  (+info)

Molecular mechanisms of thyroid hormone-stimulated steroidogenesis in mouse leydig tumor cells. Involvement of the steroidogenic acute regulatory (StAR) protein. (8/7966)

Using a mouse Leydig tumor cell line, we explored the mechanisms involved in thyroid hormone-induced steroidogenic acute regulatory (StAR) protein gene expression, and steroidogenesis. Triiodothyronine (T3) induced a approximately 3.6-fold increase in the steady-state level of StAR mRNA which paralleled with those of the acute steroid response ( approximately 4.0-fold), as monitored by quantitative reverse transcriptase-polymerase chain reaction assay and progesterone production, respectively. The T3-stimulated progesterone production was effectively inhibited by actinomycin-D or cycloheximide, indicating the requirement of on-going mRNA and protein synthesis. T3 displayed the highest affinity of [125I]iodo-T3 binding and was most potent in stimulating StAR mRNA expression. In accordance, T3 significantly increased testosterone production in primary cultures of adult mouse Leydig cells. The T3 and human chorionic gonadotropin (hCG) effects on StAR expression were similar in magnitude and additive. Cells expressing steroidogenic factor 1 (SF-1) showed marginal elevation of StAR expression, but coordinately increased T3-induced StAR mRNA expression and progesterone levels. In contrast, overexpression of DAX-1 markedly diminished the SF-1 mRNA expression, and concomitantly abolished T3-mediated responses. Noteworthy, T3 augmented the SF-1 mRNA expression while inhibition of the latter by DAX-1 strongly impaired T3 action. Northern hybridization analysis revealed four StAR transcripts which increased 3-6-fold following T3 stimulation. These observations clearly identified a regulatory cascade of thyroid hormone-stimulated StAR expression and steroidogenesis that provides novel insight into the importance of a thyroid-gonadal connection in the hormonal control of Leydig cell steroidogenesis.  (+info)

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