Paläontologisches Institut und Museum, Universität Zürich, Zürich, Switzerland.
Biol Lett. 2012 Feb 23;8(1):74-7. doi: 10.1098/rsbl.2011.0494. Epub 2011 Jul 13.
Talpid moles across all northern continents exhibit a remarkably large, sickle-like radial sesamoid bone anterior to their five digits, always coupled with a smaller tibial sesamoid bone. A possible developmental mechanism behind this phenomenon was revealed using molecular markers during limb development in the Iberian mole (Talpa occidentalis) and a shrew (Cryptotis parva), as shrews represent the closest relatives of moles but do not show these conspicuous elements. The mole's radial sesamoid develops later than true digits, as shown by Sox9, and extends into the digit area, developing in relation to an Msx2-domain at the anterior border of the digital plate. Fgf8 expression, marking the apical ectodermal ridge, is comparable in both species. Developmental peculiarities facilitated the inclusion of the mole's radial sesamoid into the digit series; talpid moles circumvent the almost universal pentadactyly constraint by recruiting wrist sesamoids into their digital region using a novel developmental pathway and timing.
所有的北大陆獭形狸尾兽都在前肢的五个趾骨前有一个明显较大的镰状籽骨，总是伴随着一个较小的胫骨籽骨。在伊比利亚鼹鼠（Talpa occidentalis）和鼩鼱（Cryptotis parva）的肢体发育过程中使用分子标记物揭示了这一现象背后的一种可能的发育机制，因为鼩鼱是鼹鼠最接近的亲属，但它们没有表现出这些明显的元素。如 Sox9 所示，鼹鼠的桡籽骨比真正的趾骨发育得晚，并延伸到趾骨区域，与数字板前缘的 Msx2 结构域有关。Fgf8 表达，标记顶外胚层嵴，在两个物种中是可比的。发育的特殊性使得鼹鼠的桡籽骨能够纳入趾骨系列；獭形狸尾兽通过使用一种新的发育途径和时间，将腕籽骨招募到其数字区域，从而规避了几乎普遍的五指性约束。
