A subset of nuclear-encoded RNAs has to be imported into mitochondria for the proper replication and transcription of the mitochondrial genome and, hence, for proper mitochondrial function. Polynucleotide phosphorylase (PNPase or PNPT1) is one of the very few components known to be involved in this poorly characterized process in mammals. At the organismal level, however, the effect of PNPase dysfunction and impaired mitochondrial RNA import are unknown. By positional cloning, we identified a homozygous PNPT1 missense mutation (c.1424A>G predicting the protein substitution p.Glu475Gly) of a highly conserved PNPase residue within the second RNase-PH domain in a family affected by autosomal-recessive nonsyndromic hearing impairment. In vitro analyses in bacteria, yeast, and mammalian cells showed that the identified mutation results in a hypofunctional protein leading to disturbed PNPase trimerization and impaired mitochondrial RNA import. Immunohistochemistry revealed strong PNPase staining in the murine cochlea, including the sensory hair cells and the auditory ganglion neurons. In summary, we show that a component of the mitochondrial RNA-import machinery is specifically required for auditory function.
Our results suggest that the frequency of Y chromosome AZF microdeletions is elevated in individuals with severe spermatogenic failure and that gr/gr deletions are not associated with spermatogenic failure.
The methylenetetrahydrofolate reductase (MTHFR) gene is one of the main regulatory enzymes involved in folate metabolism, DNA synthesis and remethylation reactions. The influence of MTHFR variants on male infertility is not completely understood. The objective of this study was to analyze the distribution of the MTHFR C677T and A1298C variants using PCR-Restriction Fragment Length Polymorphism (RFLP) in a case group consisting of 344 men with unexplained reduced sperm counts compared to 617 ancestry-matched fertile or normozoospermic controls. The Chi square test was used to analyze the genotype distributions of MTHFR polymorphisms. Our data indicated a lack of association of the C677T variant with infertility. However, the homozygous (C/C) A1298C polymorphism of the MTHFR gene was present at a statistically high significance in severe oligozoospermia group compared with controls (OR = 3.372, 95% confidence interval CI = 1.27–8.238; p = 0.01431). The genotype distribution of the A1298C variants showed significant deviation from the expected Hardy-Weinberg equilibrium, suggesting that purifying selection may be acting on the 1298CC genotype. Further studies are necessary to determine the influence of the environment, especially the consumption of diet folate on sperm counts of men with different MTHFR variants.
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