Turning off a gene early in mouse development led researchers to end up with an accidental six-legged embryonic mammal.
The team compared 10 to 17-day-old mouse embryos with and without functioning versions of the gene in question, Tgfbr1, which codes for the Tgfbr1 receptor protein.
Tgfbr1 contributes to a signaling pathway that gives a forming body its trunk-to-tail directions.
This pathway provides a 'create a hindlimb' here, or 'external genitals' instructions to the developing embryo's cells.
While legs and arms share many of the same genes, this early in the process, the hindlimbs and genitals have more in common.
The scientists found that despite the rather dramatically different placement of the extra legs in the embryos without a functioning version of Tgfbr1, the other genes expressed in these legs are similar to those found in normal mouse limbs.
The researchers still don't know the exact mechanism between the Tgfbr1 gene suppression leading to an extra pair of legs. »
