Tgfbr1 controls developmental plasticity between the hindlimb and external genitalia by remodeling their regulatory landscape
The hindlimb and external genitalia of present-day tetrapods are thought to derive from an ancestral common primordium that evolved to generate a wide diversity of structures adapted for efficient locomotion and mating in the ecological niche conquered by the species. We show that despite long evolutionary distance from the ancestral condition, the early primordium of the mouse external genitalia preserved the capacity to take hindlimb fates. In the absence of Tgfbr1, the pericloacal mesoderm generates an extra pair of hindlimbs at the expense of the external genitalia. It has been shown that the hindlimb and the genital primordia share many of their key regulatory factors. Tgfbr1 controls the response to those factors acting in a pioneer-like mode to modulate the accessibility status of regulatory elements that control the gene regulatory networks leading to the formation of genital or hindlimb structures. Our work uncovers a remarkable tissue plasticity with potential implications in the evolution of the hindlimb/genital area of tetrapods, and identifies a novel mechanism for Tgfbr1 activity that might also contribute to the control of other physiological or pathological processes. Overall design: Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) performed on control hindlimb and genital tubercle (GT) and on Tgfbr1 conditional knock out (cKO) extra hindlimb and GT.