Gene Structure Evolution of the Short-Chain Dehydrogenase/Reductase (SDR) Family

SDR (Short-chain Dehydrogenases/Reductases) are one of the oldest and heterogeneous superfamily of proteins, whose classification is problematic because of the low percent identity, even within families. To get clearer insights into SDR molecular evolution, we explored the splicing site organization of the 75 human SDR genes across their vertebrate and invertebrate orthologs. We found anomalous gene structures in members of the human SDR7C and SDR42E families that provide clues of retrogene properties and independent evolutionary trajectories from a common invertebrate ancestor. The same analyses revealed that the identity value between human and invertebrate nonallelic variants is not necessarily associated with the homologous gene structure. Accordingly, a revision of the SDR nomenclature is proposed by including the human SDR40C1 and SDR7C gene in the same family.