Moles live in holes. As such they don't need perfect eyesight, a trait that has been modified by natural selection. And now for the first time, scientists have provided a genetic explanation for it.
The Iberian mole, Talpa occidentalis, is a curious looking cove, with its star-nose and permanently closed eyes. It has so intrigued scientists that they wanted to study the basic genetics of its lens development to see why it lives in the dark.
The research was carried out by a team of scientists led by J Martin Collinson from the University of Aberdeen and it's the first full study of the basic genetics of lens development in a subterranean animal. It was published in BMC Biology.
The team wanted to find out what was going on in embryogenesis when the mole was developing. They found that the lack of eyesight in the Iberian mole was not due to some kind of genetic disorder that appeared in adult life but because the lens developmental process stops at some point. It starts normally, but then goes no further.
The basic genetics of this is down to several of the genes that the scientists studied - PAX6, FOXE3 and beta-crystallin genes.
PAX6
This is usually down regulated in the lens fibres of other species. It was not in the Iberian mole.
FOXE3
Expressed ectopically in the Iberian mole.
Beta-Crystallin Genes
These are not regulated by the same collection of genes that are seen in other vertebrates.
The effect of the changes seen in these genes is that the adult lens is in part composed of a disrupted epithelium and immature fibre cells. It was revealed by this study that although eye lens development starts normally in the Iberian mole, the defects begin to appear after the closure of the lens vesicle.
There is a considerably active area of scientific research that's probing the role that PAX6 plays in eye development and disease. For example in humans, mutations of the PAX6 gene leads to many people suffering from multiple eye abnormalities, including cataract and glaucoma. It may be that these studies can be complemented by work on the Iberian mole as the basic genetics and eye anatomy, to a certain degree, are similar.