Abstract

Northern blot analysis of testis and sperm RNA probed with clone MS-134 isolated from mouse cDNA library, indicated that the corresponding RNA was enriched in the gamete. The sequence contains an invert repeat of 120 bp at the 5' end of the 16S mtRNA. Amplification of mtDNA of sperm and other somatic tissues produced a single fragment of 342 bp indicating that the RNA of clone 134 is a post-transcription product. RT-PCR of total sperm heads RNA suggested that the 16S rRNA was localized in the nucleus of mouse, rat and human sperm. This unusual localization of a mitochondrial transcript was confirmed by In Situ hybridization (ISH) assays. The antisense oligo labeled with digoxigenin hybridized with the sperm nucleus and midpiece, while the sense probe yielded negative results. A working hypothesis is that this novel RNA may play a role in cell proliferation and differentiation. Human HL60 cells provided an adequate system to test this possibility. ISH showed overexpression of the 16S mtRNA in HL-60. Treatment of these cells with phorbol ester (TPA) induced, both, differentiation to macrophage and, a sharp decrease in the content of the 16S mtRNA. Finally, overexpression of the 16S mtRNA was also found in normal human lymphocytes stimulated with PHA by 72 hrs. These results suggest that overexpression of the 16S mtRNA is a novel participant in cell proliferation (FONDECYT N 196-0492 and 296-0062).