Scientists Create a Six-Legged Mouse Embryo, Adding a Pair of Hind Legs Instead of External Genitalia.
Moisés Mallo, a biologist at the Gulbenkian Science Institute in Oeiras, Portugal, and his team are studying one of the Tgfbr1 receptor proteins involved in signaling pathways related to various aspects of embryonic development. They disabled the Tgfbr1 gene in mid-gestation mouse embryos to investigate its impact on spinal cord development, as reported by Interesting Engineering on April 2.
Normal four-legged mouse embryo (left) and six-legged mouse without external genitalia (right). (Photo: Nature)
The Tgfbr1 gene provides instructions for producing a protein known as the transforming growth factor beta receptor type 1. Transmitted by the TGF-β receptor complex, these signals activate various cellular responses, including growth and cell division. The TGF-β type 1 receptor helps prevent cells from growing and dividing too rapidly or uncontrollably, potentially inhibiting tumor formation. More than ten mutations in the Tgfbr1 gene increase the risk of developing a form of skin cancer. A rare syndrome known as Ferguson-Smith disease leads to the formation of multiple invasive skin tumors that develop uncontrollably over weeks. These tumors then suddenly shrink, leaving scars.
According to Nature, Mallo’s student, Anastasiia Lozovska, visited his office and reported that she had discovered one of the genetically modified embryos with external genitalia resembling two additional hind legs.
In many four-legged animals, external genitalia and hind legs develop from the same initial structure. The research team found that Tgfbr1 directs these structures to become either genitalia or legs. In other words, disabling this protein alters the activity of other genes. As a result, the animal develops extra legs and lacks external genitalia.
The mice used to create the embryos were between 3 to 6 months old. The research team collected the mouse embryos through dissection and processed them for further analysis. They did not include detailed analysis of the embryos’ sex, as the external genitalia of males and females showed no differences.
Currently, the researchers plan to investigate whether Tgfbr1 and related genes affect DNA structure in other systems, such as metastatic cancer. They also want to determine if a similar process could lead to the development of double penises in reptiles.
