SCaMC-1Like a Member of the Mitochondrial Carrier (MC) Family Preferentially Expressed in Testis and Localized in Mitochondria and Chromatoid Body

Mitochondrial carriers (MC) form a highly conserved family involved insolute transport across the inner mitochondrial membrane in eukaryotes. Inmammals, ATP-Mg/Pi carriers, SCaMCs, form the most complex subgroup with fourparalogs, SCaMC-1, -2, -3 and -3L, and several splicing variants. Here, wereport the tissue distribution and subcellular localization of a mammalian-specificSCaMC paralog, 4930443G12Rik/SCaMC-1Like (SCaMC-1L),which displays unanticipated new features. SCaMC-1L proteins show higher aminoacid substitution rates than its closest paralog SCaMC-1. In mouse, SCaMC-1Lexpression is restricted to male germ cells and regulated during spermatogenesisbut unexpectedly its localization is not limited to mitochondrial structures.In mature spermatids SCaMC-1L is detected in the mitochondrial sheath butin previous differentiation stages appears associated to cytosolic granuleswhich colocalize with specific markers of the chromatoid body (CB) in post-meioticround spermatids and inter-mitochondrial cement (IMC) in spermatocytes. Theorigin of this atypical distribution was further investigated by transientexpression in cell lines. Similarly to male germ cells, in addition to mitochondrialand cytosolic distribution, a fraction of SCaMC-1L-expressing COS-7 cellsdisplay cytosolic SCaMC-1L-aggregates which exhibit aggresomal-like featuresas the CB. Our results indicate that different regions of SCaMC-1L hinderits import into mitochondria and this apparently favours the formation ofcytosolic aggregates in COS-7 cells. This mechanism could be also operationalin male germ cells and explain the incorporation of SCaMC-1L into germinalgranules.