Development and evolution of the mammalian limb: adaptive diversification of nails, hooves, and claws
Development and evolution of the mammalian limb: adaptive diversification of nails, hooves, and claws
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DOI：
10.1046/j.1525-142x.2001.01032.x
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发表时间：
2001-09-01
影响因子：
2.9
通讯作者：
Hamrick, MW
中科院分区：
文献类型：
--
作者：
Hamrick, MW
古生物学证据表明，哺乳动物在新生代早期的进化多样化是以远端肢体结构的适应性辐射为特征的。同样，新的数据表明，远端肢体附属物(如指甲、蹄子和爪子)的形态变化不仅可以在遥远的哺乳动物类群之间观察到，而且在同一支系中密切相关的物种之间也可以观察到。对指甲、爪子和蹄的形态发生的比较分析表明，在这些成人远端肢体附属物形态的差异背后，间质和上皮型式存在着相对微小的差异。此外，对脊椎动物爪子发育过程中调控基因表达的研究表明，许多参与形成外胚层衍生品图案的信号分子，如牙齿、毛发和羽毛，也参与组织哺乳动物的远端肢体附件。例如，Bmp4信号在间充质细胞募集到形成末端指骨的凝聚体中发挥重要作用，而MSX2通过抑制生发表皮细胞的增殖来影响指甲和爪子的长度。因此，远端皮肤附属物形式的进化变化可能是由于间充质凝聚形成过程中基因表达的变化(Bmp4，后部Hox基因)，爪状基质和生发基质(Shh)的诱导，和/或爪状基质中表皮细胞的增殖(Msx1，MSx2)。哺乳动物指甲和爪子结构的趋同性和平行性的普遍存在，突显了远端肢体附属物存在多种形态发生的进化变化途径。
Paleontological evidence indicates that the evolutionary diversification of mammals early in the Cenozoic era was characterized by an adaptive radiation of distal limb structures. Likewise, neontological data show that morphological variation in distal limb integumentary appendages (e.g., nails, hooves, and claws) can be observed not only among distantly related mammalian taxa but also among closely related species within the same clade. Comparative analysis of nail, claw, and hoof morphogenesis reveals relatively subtle differences in mesenchymal and epithelial patterning underlying these adult differences in distal limb appendage morphology. Furthermore, studies of regulatory gene expression during vertebrate claw development demonstrate that many of the signaling molecules involved in patterning ectodermal derivatives such as teeth, hair, and feathers are also involved in organizing mammalian distal limb appendages. For example, Bmp4 signaling plays an important role during the recruitment of mesenchymal cells into the condensations forming the terminal phalanges, whereas Msx2 affects the length of nails and claws by suppressing proliferation of germinal epidermal cells. Evolutionary changes in the form of distal integumentary appendages may therefore result from changes in gene expression during formation of mesenchymal condensations (Bmp4, posterior Hox genes), induction of the claw told and germinal matrix (shh), and/or proliferation of epidermal cells in the claw matrix (Msx1, Msx2). The prevalence of convergences and parallelisms in nail and claw structure among mammals underscores the existence of multiple morphogenetic, pathways for evolutionary change in distal limb appendages.