Aoki Motoko, Kiyonari Hiroshi, Nakamura Harukazu, Okamoto Hitoshi
Laboratory for Developmental Gene Regulation, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Dev Growth Differ. 2008 Feb;50(2):85-95. doi: 10.1111/j.1440-169X.2007.00978.x. Epub 2007 Dec 7.
Mouse R-spondin2 (Rspo2) is a member of the R-spondin protein family, which is characterized by furin-like cysteine-rich domains and a thrombospondin type 1 repeat. R-spondin is a secreted molecule that activates Wnt/beta-catenin signaling. Rspo2-deficient mice were generated to investigate the function of mouse Rspo2 during embryonic development. The homozygous mutant forelimb showed defects in distal phalanges and nail structures, and the digits were anomalous in shape. The homozygous mutant hindlimb showed more severe malformations, including lack of digits and zeugopod components. Rspo2 is expressed in the apical ectodermal ridge (AER) of the developing limb. Fgf8 expression in the AER was significantly lower in the homozygous mutant forelimb than in the wild-type forelimb and it was disturbed along the dorsoventral axis. In the homozygous mutant hindlimb, Fgf8 and Fgf4 expression in the posterior AER and Sonic hedgehog expression in the zone of polarizing activity (ZPA) were reduced. The homozygous mutant hindlimb also showed expansion of Wnt7a expression in the dorsal ectoderm toward the ventral side. This study shows that Rspo2 is critical for maintenance of the AER and for growth and patterning in limb development.
小鼠R-spondin2（Rspo2）是R-spondin蛋白家族的成员，其特征在于富含弗林蛋白酶样半胱氨酸的结构域和血小板反应蛋白1型重复序列。R-spondin是一种分泌分子，可激活Wnt/β-连环蛋白信号通路。为了研究小鼠Rspo2在胚胎发育过程中的功能，构建了Rspo2基因缺陷型小鼠。纯合突变体的前肢在远端指骨和指甲结构上出现缺陷，并且指的形状异常。纯合突变体的后肢表现出更严重的畸形，包括指的缺失和小腿部分的缺失。Rspo2在发育中的肢体的顶端外胚层嵴（AER）中表达。纯合突变体前肢AER中的Fgf8表达明显低于野生型前肢，并且沿背腹轴受到干扰。在纯合突变体后肢中，后AER中的Fgf8和Fgf4表达以及极化活性区（ZPA）中的音猬因子表达均降低。纯合突变体后肢还显示背侧外胚层中Wnt7a表达向腹侧扩展。这项研究表明，Rspo2对于维持AER以及肢体发育中的生长和模式形成至关重要。
