Six-Limbed Mouse Embryo Developed By Scientists With Extra Pair of Hindlimbs Rather Than Genitals

Scientists were able to develop a mouse embryo with six legs. The embryo has an extra pair of hindlimbs that were developed at the expense of their external genitals.

Animal Embryonic Development

The rudimentary mouse could offer crucial insights regarding early animal development stages. It may also unravel mysteries regarding human evolution.

Everyone starts microscopically as a limbless bean that grows legs and arms gradually. This growth results from a complex chemical instruction network. Such instructions tell particular genes to turn on or off, depending on their exact location within the body. Over time and growth, these instructions become more specific.

The TGF-β family of growth factors is one crucial chemical instruction group. In order to respond to such growth factors, cells make a complementary receptor family. One vital receptor called the Tgfβ receptor 1 (Tgfbr 1) plays a crucial role in controlling hindlimb and external genitalia formation.

To delve deeper into this chemical crosstalk's role when it comes to embryonic development, a research team from the Gulbenkian Science Institute in Portugal deactivated a specific gene that encodes the Tgfbr1 receptor halfway through the mouse's embryonic development. Findings were documented in the "Tgfbr1 controls developmental plasticity between the hindlimb and external genitalia by remodeling their regulatory landscape" study.

ALSO READ: Lab-Grown Human Embryos Developed as Models Bearing Features of Typical 2-Week-Olds

Two Additional Hindlimbs Developed in Place of External Genitals

The team was originally interested in how the gene expression changes could affect the spinal cord's development. However, what they found was something that was completely unexpected: two additional hindlimbs developed in place of the mouse's external genitalia.

The researchers also found that the Tgfbr1 dictates whether the limb buds grow into genitals or hindlimbs by changing how DNA folds within the cells of such limb structures. Hence, by inactivating the Tgfbr1, the researchers inadvertently altered the expressions of other genes within the embryonic cells of the mouse. This led to the formation of an extra leg pair.

The authors note that their study sheds light on great tissue plasticity with potential implications in the evolution of the genital area or hindlimbs of four-legged animals. They hope that by boosting understanding of such pathways, crucial insights regarding the mechanisms behind different developmental diseases could be gained.

Though the studies were done in mouse models, early developmental pathways are quite conserved across various mammals. This is due to how minimal changes in function could lead to drastic and usually detrimental impacts on the growing organism's development. Hence, a lot of what is known from mouse embryos can be translated to human development.

The researchers plan to look into whether Tgfbr1 and its relatives could affect other system's DNA structure, such as in the case of metastatic cancer. They also want to know if this process is also behind the development of the double penis, or hemipenis, of reptiles.

Check out more news and information on Genetics in Science Times.