Rat testicular myotubularin, a protein tyrosine phosphatase expressed by Sertoli and germ cells, is a potential marker for studying cell-cell interactions in the rat testis

The full-length cDNA encoding the entire open reading frame (ORF) of rat my otubularin (rMTM) was isolated from a rat testis expression library by PCR. Among the three similar to2.9-kb cDNAs that were sequenced, one clone was different from the other two clones. It contained seven extra amino acids o f FVVLNLQ; this short stretch of extra sequence was found between Gln(421) and Phe(422) within the SET (Suvar3-9, Enhancer-of-zeste, Trithorax) intera cting domain (SID) of rMTM. The rMTM ORF had 1,713 bp encoding for a 571 am ino acid polypeptide and a calculated molecular weight of 65.8 kDa. A compa rison between its deduced amino acid sequence and the GenBank database usin g BLAST revealed a 53.1% identity with human myotubularin protein (hMTM1), which is a member of the protein tyrosine phosphatase (PTP) family associat ed with X-linked myotubular myopathy. A 22 amino acid peptide NH2-TKVNERYEL CDTYPALLAVPAN was synthesized based on the deduced amino acid sequence of r MTM and used for antibody production. By using immunoblot analysis, a 66-kD a protein was indeed detected in both Sertoli and germ-cell cytosols. rMTM mRNA was found in various tissues but was predominantly expressed in the te stis, ovary, and skeletal muscle. Sertoli cell rMTM expression was stimulat ed by germ cells and enhanced when inter-Sertoli junctions were being assem bled in vitro. A drastic reduction in testicular rMTM steady-state mRNA lev el correlated with the depletion of germ cells from the testis in vivo foll owing either glycerol or lonidamine treatment. These results indicate that rMTM is a rat homologue of hMTM1 that may be a useful marker in monitoring the events of cell-cell interactions in the testis. J. Cell. Physiol. 185:3 66-385, 2000. (C) 2000 Wiley-Liss, Inc.