Characterization of POMT2, a novel member of the PMT protein O-mannosyltransferase family specifically localized to the acrosome of mammalian spermatids

Abstract

Over the past few years it has emerged that O-mannosyl glycans are not restricted to yeasts and fungi but are also present in higher eukaryotes, including humans. They play a substantial role in the onset of muscular dystrophy and neuronal migration disorders, like muscle-eye-brain disease. Protein O-mannosyltransferase genes (PMTs) are evolutionarily conserved from yeast to human; however, little is known about these enzymes in higher eukaryotes. In this study, we cloned the first PMT2 subfamily members from human (hPOMT2), mouse (mPomt2), and Drosophila (DmPOMT2). A detailed characterization of the mammalian POMT2, with emphasis on mouse Pomt2, shows that mammalian POMT2 is predominantly expressed in testis tissue. Due to differential transcription initiation of the mPomt2 gene, two distinct mRNA species that vary in length are formed. The shorter transcript is present in all somatic tissues examined. Expression of the corresponding hPOMT2 cDNA in mammalian cells identified POMT2 as an integral membrane protein of the endoplasmic reticulum with an apparent molecular weight of 83 kDa. The longer mPomt2 transcript is restricted to testis and encodes a testis-specific mPOMT2 protein isoform. Using in situ hybridization and immunolocalization, we demonstrate that in testis tissue mPOMT2 localizes to maturing spermatids and is abundant within the acrosome, a sperm-specific organelle essential for fertilization. Our data suggest a novel and specific role for the putative protein O-mannosyltransferase POMT2 in the maturation and/or function of sperm in mammals.

The Twisted Abdomen Phenotype of Drosophila POMT1 and POMT2 Mutants Coincides with Their Heterophilic Protein O-Mannosyltransferase Activity

“…RE38203 contains a 2658-bp ORF encoding a dPOMT1 protein of 886 amino acids (GenBank TM /EBI accession number AB176550), and LP01681 contains a 2295-bp ORF encoding a dPOMT2 protein of 765 amino acids (GenBank TM /EBI accession number AB176551) (11). A ClustalW alignment of dPOMT1 and dPOMT2 showed 42 and 52% homology to hPOMT1 and hPOMT2, respectively (Fig.…”

“…There are two human protein O-mannosyltransferase (POMT) homologs, hPOMT1 and hPOMT2, which belong to the PMT4 and PMT2 subfamilies, respectively (11). Mutations in the hPOMT1 gene give rise to the severe neuronal migration disorder, Walker-Warburg syndrome (12).…”

“…Drosophila has two POMT orthologs, dPOMT1 and dPOMT2, which correspond to human hPOMT1 and hPOMT2, respectively (11). The dPOMT1 mutants are known to have reduced viability, whereas escaper flies show the so-called twisted abdomen phenotype that is caused by pronounced de-fects in muscle development (10).…”

Novel cardiovascular findings in association with a POMT2 mutation: three siblings with α-dystroglycanopathy

“…3 Protein O-mannosyltransferase 2 (POMT2) is a 21-exon gene that encodes an integral membrane protein of the endoplasmic reticulum required for the correct glycosylation of a-dystroglycan. 4,5 Both POMT1 and POMT2 mutations are the most common causes of WWS. 1, 2,6,7 Cardiac involvement among the dystroglycanopathies remains poorly characterized.…”

Members of the Evolutionarily Conserved PMT Family of ProteinO-Mannosyltransferases Form Distinct Protein Complexes among Themselves

“…Second, the PMT1/PMT2 and PMT4 subfamilies use distinct acceptor protein substrates in vivo (9,14). Third, in fungi the PMT1/PMT2 subfamily is highly redundant, whereas the PMT4 subfamily has only one representative per species (17,18).…”