A group of scientists from the Gulbenkian Institute of Science in Portugal conducted an experiment where they created an embryo mouse with six limbs, replacing the external genital organs with an additional pair of hind legs. The results of this study were published in the journal Nature Communications, opening up new horizons for understanding the early stages of animal development and shedding light on the secrets of evolution.
During the early stages of life, a complex development process begins where limbs are formed under the influence of chemical signals. One crucial group of these signals is the TGF-β growth factors. Among these factors, the TGFβ 1 receptor plays a vital role in controlling the development of hind limbs and external genital organs.
Under the guidance of Moses Mallo, the researchers deactivated the gene encoding the TGFBR1 receptor in mouse embryos midway through their development. In a surprising turn of events, instead of affecting the development of the spinal cord as expected, an additional pair of hind legs developed in place of the external genital organs.
Further research revealed that TGFBR1 determines which structures will evolve into limb rudiments – hind legs or genitals – by altering the DNA arrangement in the cells of these structures. Deactivating TGFBR1 caused changes in gene expression in the mouse embryo cells, resulting in the emergence of an extra pair of legs.
The study’s authors highlighted the remarkable flexibility of tissues, which can have implications for understanding the evolution of the hind limbs/genitals region in quadrupeds. These findings have the potential to enhance our comprehension of early development stages and the mechanisms underlying various developmental disorders. While the experiments were conducted on mice, many early developmental processes are similar in different mammals, allowing for the extrapolation of the data to humans.