For the first time, Portuguese scientists created a 6-legged mouse

Scientists created a six-legged mouse embryo, with an extra pair of hind legs instead of external genitalia .

Moisés Mallo, a biologist at the Gulbenkian Institute of Sciences in Oerias, Portugal, and his colleagues are studying one of the receptor proteins Tgfbr1 , a signaling pathway involved in many aspects of embryonic development. They stopped the activity of the Tgfbr1 gene in mid-pregnancy mouse embryos to understand its effects on spinal cord development, Interesting Engineering reported on April 2.

Normal 4-legged mouse embryo (left) and 6-legged mouse embryo but no external genitalia (right). (Photo: Nature)

The Tgfbr1 gene provides instructions for making a protein called transforming growth factor beta type 1 receptor . Transmitted by the TGF-β receptor complex , these signals trigger a variety of cellular responses, including cell growth and division. TGF-β type 1 receptor helps prevent cells from growing and dividing too quickly or in an uncontrolled way, which can inhibit tumor formation. More than 10 mutations in the Tgfbr1 gene increase the risk of developing a form of skin cancer. A rare syndrome called Ferguson - Smith disease leads to the formation of multiple invasive skin tumors that grow uncontrollably over several weeks. These tumors then suddenly shrink and leave scars.

According to Nature, Mallo's student Anastasiia Lozovska came to his office and announced that she had discovered one of the bio-edited embryos with genitalia similar to two additional hind legs.

In many quadrupeds, the external genitalia and hind legs develop from the same original structure. The team found that Tgfbr1 instructs those structures to become genitals or legs. In other words, inactivating a protein changes the activity of other genes. As a result, the animal has extra legs and no external genitalia.

Mice used to create embryos are between 3 - 6 months old. The research team collected mouse embryos by dissection and processed them for further analysis. They did not include detailed analysis of embryonic sex because the external genitalia of males and females do not differ.

Now, the researchers plan to investigate whether Tgfbr1 and related genes affect DNA structure in other systems, such as metastatic cancer. They also wanted to know if the same process causes reptiles to develop double penises.