Human mitochondrial RNA turnover caught in flagranti: involvement of hSuv3p helicase in RNA surveillance

The mechanism of human mitochondrial RNA turnover and surveillance is still a matter of debate. We have obtained a cellular model for studying the role of hSuv3p helicase in human mitochondria. Expression of a dominant-negative mutant of the hSUV3 gene which encodes a protein with no ATPase or helicase activity results in perturbations of mtRNA metabolism and enables to study the processing and degradation intermediates which otherwise are difficult to detect because of their short half-lives. The hSuv3p activity was found to be necessary in the regulation of stability of mature, properly formed mRNAs and for removal of the noncoding processing intermediates transcribed from both H and L-strands, including mirror RNAs which represent antisense RNAs transcribed from the opposite DNA strand. Lack of hSuv3p function also resulted in accumulation of aberrant RNA species, molecules with extended poly(A) tails and degradation intermediates truncated predominantly at their 3′-ends. Moreover, we present data indicating that hSuv3p co-purifies with PNPase; this may suggest participation of both proteins in mtRNA metabolism

Positive Selection Shaped the Convergent Evolution of Independently Expanded Kallikrein Subfamilies Expressed in Mouse and Rat Saliva Proteomes

We performed proteomics studies of salivas from the genome mouse (C57BL/6 strain) and the genome rat (BN/SsNHsd/Mcwi strain). Our goal was to identify salivary proteins with one or more of three characteristics that may indicate that they have been involved in adaptation: 1) rapid expansion of their gene families; 2) footprints of positive selection; and/or 3) sex-limited expression. The results of our proteomics studies allow direct comparison of the proteins expressed and their levels between the sexes of the two rodent species. Twelve members of the Mus musculus species-specific kallikrein subfamily Klk1b showed sex-limited expression in the mouse saliva proteomes. By contrast, we did not find any of the Rattus norvegicus species-specific kallikrein subfamily Klk1c proteins in male or female genome rat, nor transcripts in their submandibular glands. On the other hand, we detected expression of this family as transcripts in the submandibular glands of both sexes of Sprague-Dawley rats. Using the CODEML program in the PAML package, we demonstrate that the two rodent kallikrein subfamilies have apparently evolved rapidly under the influence of positive selection that continually remodeled the amino acid sites on the same face in the members of the subfamilies. Thus, although their kallikrein subfamily expansions were independent, this evolutionary pattern has occurred in parallel in the two rodent species, suggesting a form of convergent evolution at the molecular level. On the basis of this new data, we suggest that the previous speculative function of the species-specific rodent kallikreins as important solely in wound healing in males be investigated further. In addition to or instead of that function, we propose that their sex-limited expression, coupled with their rapid evolution may be clues to an as-yet-undetermined interaction between the sexes

Differential expression of inhibin alpha and beta A subunit genes in rat and mouse ovarian follicles during pregnancy

Relative levels of rat ovarian alpha inhibin (alpha I) and beta A inhibin (beta AI) mRNAs were measured during pregnancy by dot-blot hybridization of ovarian poly(A+) RNA. Follicular patterns of alpha I and beta AI expression in contralateral ovaries from the same rats were also studied by hybridization histochemistry. Oligodeoxynucleotide probes specific for porcine alpha I and beta AI were synthesized, 32P end-labelled and used as hybridization probes on dot-blots of ovarian RNA and frozen sections of ovarian tissue from pregnant rats. During pregnancy, levels of alpha I and beta AI mRNAs remained fairly constant from day 7 after mating until parturition and then fell within 16 h post partum. In all ovaries observed, expression of inhibin genes was located in granulosa cells of healthy antral follicles. In general, the strongest signals for alpha I and beta AI mRNAs were obtained in large follicles, with weaker signals in smaller follicles. Follicular patterns of alpha I and beta AI expression during pregnancy were often dissimilar when alpha I and beta AI were compared over a range of follicles. Considerable alpha I mRNA was detectable in some follicles in which beta AI was reduced or undetectable, despite strong signals for both alpha I and beta AI in an adjacent follicle. Essentially, alpha I mRNA levels were relatively consistent between groups of follicles, whereas beta AI levels varied considerably. beta AI mRNA was never observed in a follicle in the absence of alpha I mRNA, indicating that activin production in any follicle occurs in the presence of alpha I mRNA. (ABSTRACT TRUNCATED AT 250 WORDS)