Figure 1.

The limb‐specific conditional knockout (cKO) of Acvr1 leads to skeletal malformations in phalanges and metacarpals. Extremities of wild‐type mice and Prx1‐Cre‐Acvr1(fl/fl) mice (cKO) were prepared and stained for cartilage (Alcian blue) and/or bone (Alizarin red) structures. A: After conditional Acvr1 knockout, mice in stage P1 develop a malformation of phalangeal and metacarpal bones, whereat especially the first digit is shortened (arrow) and shows additional cartilaginous elements in the distal part (asterisk) surrounded by connective tissue. The development of stylo‐ and zeugopod of mice in stage P1 was not affected by Acvr1 knockout. B: The cKO of Acvr1 leads to a shortening of skeletal elements still found in adult mice (hind limb depicted). Phalanges of cKO mice appear bended. Again, digit 1 is most affected being drastically shortened due to missing phalanges (arrows). Additional calcified elements are found in the distal part of the digit as well (asterisks)