Placental hormones and syncytins in the blind mole rat
A blind mole rat Spalax ehrenbergi (Wikimedia Commons)
Mole rats (Spalacidae) occupy a basal position in the superfamily Muroidea. The blind mole rats, Spalax spp., are highly adapted to a subterranean lifestyle. They are resistant to both spontaneous cancer and carcinogens. For all these reasons they are widely studied and now we have a description of the genome of one species S. galili and the placental transcriptome both of that species and of S. carmeli (here).
Placental-specific genes known from mouse and rat (Muridae) include cathepsins, placental lactogens (derived through duplication of the prolactin gene) and pregnancy-specific glycoproteins (reviewed here). Orthologues of many of these genes were present in Spalax and given the basal position of Spalacidae this indicates they had started to diversify in the last common ancestor of the muroid rodents.
Syncytins are endogenous retroviral envelope proteins thought to be essential for the formation of syncytiotrophoblast (previous post). Two such genes are known from mouse, rat (Muridae) and hamster (Cricetidae). Both are present in the Spalax genome although only Synb was confirmed in the placental transcriptome. This extends the timing of the env gene capture further back in time to an estimated 45 Mya.
Beta globin genes code for the two chains of haemoglobin molecules. One of them HBG is expressed in the embryo of most mammals but in the fetal haemoglobin of higher primates (discussed here). The HBG of Spalax shows evidence of rapid sequence evolution under positive selection. It is not clear to what extent this affects its affinity for oxygen.