Evolutionary Genomics Implies a Specific Function of Ant4 in Mammalian and Anole Lizard Male Germ Cells

Abstract

Most vertebrates have three paralogous genes with identical intron-exon structures and a high degree of sequence identity that encode mitochondrial adenine nucleotide translocase (Ant) proteins, Ant1 (Slc25a4), Ant2 (Slc25a5) and Ant3 (Slc25a6). Recently, we and others identified a fourth mammalian Ant paralog, Ant4 (Slc25a31), with a distinct intron-exon structure and a lower degree of sequence identity. Ant4 was expressed selectively in testis and sperm in adult mammals and was indeed essential for mouse spermatogenesis, but it was absent in birds, fish and frogs. Since Ant2 is X-linked in mammalian genomes, we hypothesized that the autosomal Ant4 gene may compensate for the loss of Ant2 gene expression during male meiosis in mammals. Here we report that the Ant4 ortholog is conserved in green anole lizard (Anolis carolinensis) and demonstrate that it is expressed in the anole testis. Further, a degenerate DNA fragment of putative Ant4 gene was identified in syntenic regions of avian genomes, indicating that Ant4 was present in the common amniote ancestor. Phylogenetic analyses suggest an even more ancient origin of the Ant4 gene. Although anole lizards are presumed male (XY) heterogametic, like mammals, copy numbers of the Ant2 as well as its neighboring gene were similar between male and female anole genomes, indicating that the anole Ant2 gene is either autosomal or located in the pseudoautosomal region of the sex chromosomes, in contrast to the case to mammals. These results imply the conservation of Ant4 is not likely simply driven by the sex chromosomal localization of the Ant2 gene and its subsequent inactivation during male meiosis. Taken together with the fact that Ant4 protein has a uniquely conserved structure when compared to other somatic Ant1, 2 and 3, there may be a specific advantage for mammals and lizards to express Ant4 in their male germ cells.

Characterization of two adenine nucleotide translocase paralogues in the stink bug, <i>Plautia stali</i>

“…On the other hand, the testis-specific ANT paralogue has only been detected in mammals, reptiles, and flies. [7][8][9] This paralogue appears to be necessary for the continuous supply of large amounts of ATP to meiotic cells. 10) In the desert locust, Schistocerca gregaria, the expression patterns of two ANT paralogues were analyzed, with neither being identified as a testis-specific gene.…”

Identification of adenine nucleotide translocase 4 inhibitors by molecular docking

“…In contrast, the exon/intron configuration of ANT4 is different from that of ANT1, ANT2 and ANT3, perhaps reflecting an alternate evolutionary origin 4; 20 . ANT4 has a lower sequence similarity to other ANTs (approximately 70% amino acid identity by a whole peptide sequence alignment) and has a unique amino acid sequence including extended N-terminal and C-terminal regions when compared to other ANTs 17; 20 . The differential structure provides a basis to identify a selective inhibitor of ANT4.…”

“…Most mammalian species including humans have four independent ANT family genes encoding ANT1, ANT2, ANT3 and ANT4 18; 20 . ANT1 is predominantly expressed in skeletal muscle and heart and is thought to be optimized for large and rapid ATP requirement in muscle metabolism 10 .…”

“…ANT1, ANT2 and ANT3 have an identical exon/intron structure and are highly homologous to each other (approximately 90% amino acid identity by a whole peptide sequence alignment) 4; 20 . In contrast, the exon/intron configuration of ANT4 is different from that of ANT1, ANT2 and ANT3, perhaps reflecting an alternate evolutionary origin 4; 20 .…”

“…ANT1, ANT2 and ANT3 have an identical exon/intron structure and are highly homologous to each other (approximately 90% amino acid identity by a whole peptide sequence alignment) 4; 20 . In contrast, the exon/intron configuration of ANT4 is different from that of ANT1, ANT2 and ANT3, perhaps reflecting an alternate evolutionary origin 4; 20 . ANT4 has a lower sequence similarity to other ANTs (approximately 70% amino acid identity by a whole peptide sequence alignment) and has a unique amino acid sequence including extended N-terminal and C-terminal regions when compared to other ANTs 17; 20 .…”