Temporal range: Early Miocene-Recent
|Middle East blind mole-rat, (Spalax ehrenbergi)|
Nannospalax Palmer, 1903
The genus Spalax contains the blind, fossorial, or subterranean mole rats, which are one of several types of rodents that are called "mole rats". The hystricognath mole-rats of the family Bathyergidae are completely unrelated, but some other forms are also in the family Spalacidae. Zokors (subfamily Myospalacinae) and root rats and bamboo rats (subfamily Rhizomyinae) are spalacids sometimes referred to as mole rats. Blind mole rats are in the family Spalacidae, but are unique enough to be given a separate subfamily, Spalacinae. Alternate opinions on taxonomy consider the blind mole-rats to be the only members of the family Spalacidae and rank other spalacid subfamilies as full families. Other authors group all members of the superfamily Muroidea into a single family, Muridae. The Spalacinae contains two genera and eight species. Some authorities treat all species as belonging to a single genus, Spalax.
Spalax mole rats are truly blind. Their very small eyes are completely covered by a layer of skin. Unlike many other fossorial rodents, Spalax mole rats do not have enlarged front claws and do not appear to use their forearms as a primary digging tool. Digging is almost exclusively conducted using their powerful front teeth, which are separated from the rest of the mouth by a flap of skin. When a Spalax mole rat closes its mouth, its incisors are still on the outside. Blind mole rats may have evolved from spalacids that used their front limbs to dig, because their olecranon processes are relatively large relative to the rest of their arms. The olecranon process is a part of the ulna bone where muscles attach, and digging animals tend to have enlarged olecranon processes to provide a large surface for their large and powerful muscles to attach.
Because they are completely blind, blind mole rats have been important laboratory animals in tests on how eyes and eye proteins function. It should be emphasized that although Spalax has only atrophied subcutaneous eyes and it is sightless, its circadian rhythm is kept. Few publications (Avivi et al) have proved that the circadian genes that control the biological clock are expressed in a similar manner as in sighted, aboveground mammals.
Studies on the growth of fibroblasts in vitro of Spalax judaei and Spalax golani showed that the process of necrosis replaces the role of the systematic apoptosis normally used in most organisms. Low-oxygen conditions, such as those common in blind mole rats' burrows, usually cause cells to undergo apoptosis. One study showed that in adaptation to a higher tendency of cell death, blind mole rats evolved a mutation in the tumor suppressor protein p53, also used in humans, to prevent cells from undergoing apoptosis. Human cancer patients have similar mutations, and blind mole rats were thought to be more susceptible to cancer because their cells cannot undergo apoptosis. However, after a specific amount of time (within 3 days according to one study), the cells in blind mole rats release interferon-beta (which the immune system normally uses to counter viruses) in response to overproliferation of cells caused by the suppression of apoptosis. In this case, the interferon-beta triggers cells to undergo necrosis, and this mechanism also kills cancer cells in blind mole rats. Because of tumor suppression mechanisms such as this, blind mole rats and other spalacids are resistant to cancer.
The involvement of interferon in the so-called concerted cell death of Spalax cells via necrosis was highly criticized. Serious questions have been raised on the inconsistent methodology used that led to this speculation [see discussion at: https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-11-91; Manov et al, BMC Biology , 2013]. Noteworthy, in this publication Manov et al, BMC Biology , 2013 interesting data on Spalax resistance to cancer have been documented:
8 ^ Irena Manov, Mark Hirsh, Theodore C Iancu, Assaf Malik, Nick Sotnichenko, Mark Band, Aaron Avivi and Imad Shams+ (2013) Pronounced cancer resistance in a subterranean rodent, the blind mole-rat, Spalax: in vivo and in vitro evidence. BMC Biology 
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