TMEM126A is a mitochondrial located mRNA (MLR) protein of the mitochondrial inner membrane

Background

Hereditary optic neuropathies (HONs) are a heterogeneous group of disorders that affect retinal ganglion cells (RGCs) and axons that form the optic nerve. Leber's Hereditary Optic Neuropathy and the autosomal dominant optic atrophy related to OPA1 mutations are the most common forms. Nonsyndromic autosomal recessive optic neuropathies are rare and their existence has been long debated. We recently identified the first gene responsible for these conditions, TMEM126A. This gene is highly expressed in retinal cellular compartments enriched in mitochondria and supposed to encode a mitochondrial transmembrane protein of unknown function.

Methods

A specific polyclonal antibody targeting the TMEM126A protein has been generated. Quantitative fluorescent in situ hybridization, cellular fractionation, mitochondrial membrane association study, mitochondrial sub compartmentalization analysis by both proteolysis assays and transmission electron microscopy, and expression analysis of truncated TMEM126A constructs by immunofluorescence confocal microscopy were carried out.

Results

TMEM126A mRNAs are strongly enriched in the vicinity of mitochondria and encode an inner mitochondrial membrane associated cristae protein. Moreover, the second transmembrane domain of TMEM126A is required for its mitochondrial localization.

Conclusions

TMEM126A is a mitochondrial located mRNA (MLR) that may be translated in the mitochondrial surface and the protein is subsequently imported to the inner membrane. These data constitute the first step toward a better understanding of the mechanism of action of TMEM126A in RGCs and support the importance of mitochondrial dysfunction in the pathogenesis of HON.

General significance

Local translation of nuclearly encoded mitochondrial mRNAs might be a mechanism for rapid onsite supply of mitochondrial membrane proteins.     

Mesocestoides corti (syn. vogae, cestoda): characterization of genes encoding cysteine-rich secreted proteins (CRISP)

With the aim of identifying genes involved in development and parasite adaptation in cestodes, four coding sequences were isolated from the cyclophyllidean Mesocestoides corti larval stage (tetrathyridium). Genes showed significant similarity to the cysteine-rich secreted protein (CRISP) encoding genes, a large family that includes stage and tissue-specific genes from diverse organisms, many associated with crucial biological processes. The full-length McCrisp2 cDNA encodes a predicted protein of 202 residues in length, containing 10 cysteines and a putative signal peptide. The expression level of McCrisp2 was estimated by Real-time PCR, relative to GAPDH, showing an increase of 75% in segmented worms compared to tetrathyridia. By in situ hybridization, McCrisp2 expression was localized mainly at the larvae apical region of tetrathyridia and in the proglottids of segmented worms. Taken together our results suggest a possible role for M. corti CRISP proteins as ES products, potentially involved in differentiation processes as proposed for homologs in other organisms.     

Identification of a novel splicing isoform of murine CGI-58

The comparative gene identification-58 (CGI-58) gene, mutations of which are linked to Chanarin-Dorfman syndrome, encodes a protein of the α/β hydrolase domain subfamily. We report here a new alternative splicing isoform of the murine CGI-58 gene, termed mCGI-58S. Sequence comparison indicates the lack of second and third exons in this cDNA variant. While the full-length protein displayed perilipin-dependent localization to lipid droplets, mCGI-58S showed a predominant cytoplasmic staining when expressed in cells. mCGI-58S was incapable of activating adipose triglyceride lipase but retained the capacity to acylate lysophosphatidic acid. Overexpression of mCGI-58S failed to promote lipid droplet turnover and loss of intracellular triacylglycerols. These results suggest that this splicing event may be involved in the regulation of lipid homeostasis.     

Molecular and structural analysis of C4-specific PEPC isoform from Pennisetum glaucum plays a role in stress adaptation

Phosphoenolpyruvate carboxylase is an ubiquitous cytosolic enzyme that catalyzes the ß-carboxylation of phosphoenolpyruvate (PEP) and is encoded by multigene family in plants. It plays an important role in carbon economy of plants by assimilating CO₂ into organic acids for subsequent C₄ or CAM photosynthesis or to perform several anaplerotic roles in non-photosynthetic tissues. In this study, a cDNA clone encoding for PEPC polypeptide possessing signature motifs characteristic to ZmC₄PEPC was isolated from Pennisetum glaucum (PgPEPC). Deduced amino acid sequence revealed its predicted secondary structure consisting of forty alpha helices and eight beta strands is well conserved among other PEPC homologs irrespective of variation in their primary amino acid sequences. Predicted PgPEPC quartenary structure is a tetramer consisting of a dimer of dimers, which is globally akin to maize PEPC crystal structure with respect to major chain folding wherein catalytically important amino acid residues of active site geometry are conserved. Recombinant PgPEPC protein expressed in E. coli and purified to homogeneity, possessed in vitro ß-carboxylation activity that is determined using a coupled reaction converting PEP into malate. Tetramer is the most active form, however, it exists in various oligomeric forms depending upon the protein concentration, pH, ionic strength of the media and presence of its substrate or effecters. Recombinant PgPEPC protein confers enhanced growth advantage to E. coli under harsh growth conditions in comparison to their respective controls; suggesting that PgPEPC plays a significant role in stress adaptation.     

Insight into pattern of codon biasness and nucleotide base usage in serotonin receptor gene family from different mammalian species

5-HT (5-Hydroxy-tryptamine) or serotonin receptors are found both in central and peripheral nervous system as well as in non-neuronal tissues. In the animal and human nervous system, serotonin produces various functional effects through a variety of membrane bound receptors. In this study, we focus on 5-HT receptor family from different mammals and examined the factors that account for codon and nucleotide usage variation. A total of 110 homologous coding sequences from 11 different mammalian species were analyzed using relative synonymous codon usage (RSCU), correspondence analysis (COA) and hierarchical cluster analysis together with nucleotide base usage frequency of chemically similar amino acid codons. The mean effective number of codon (ENc) value of 37.06 for 5-HT(6) shows very high codon bias within the family and may be due to high selective translational efficiency. The COA and Spearman's rank correlation reveals that the nucleotide compositional mutation bias as the major factors influencing the codon usage in serotonin receptor genes. The hierarchical cluster analysis suggests that gene function is another dominant factor that affects the codon usage bias, while species is a minor factor. Nucleotide base usage was reported using Goldman, Engelman, Stietz (GES) scale reveals the presence of high uracil (>45%) content at functionally important hydrophobic regions. Our in silico approach will certainly help for further investigations on critical inference on evolution, structure, function and gene expression aspects of 5-HT receptors family which are potential antipsychotic drug targets.