Molecular mechanisms of determination of limb region and identity

1.内脏/躯体侧板的区域化机制我们的外植体研究表明，侧板中胚层最终被分成内脏/体细胞层，沿前后轴已经区域化，他们建议这两层根据区域化来确定它们的前后模式(躯体形成前肢、侧肢和后肢，内脏形成胃、胃、肌腱、小肠和大肠)。2.前肢/后肢身份的确定我们提出了一个模型，即前肢和后肢在确定肢体同一性时存在显著差异，抑制效应在这一确定中起着重要作用(Saito et al，2002)。我们进一步研究了哪些组织或区域涉及抑制因子。翅膀水平的体节植入腿部，抑制后肢区Tbx4的表达，诱导Tbx5的表达。这些结果表明，体节可能是决定肢体识别的抑制效应的来源。3.软骨鱼的鳍发育我们构建了一个连续获得软骨鱼卵的系统，并从两种软骨鱼(鲨鱼和白鲨)中克隆了几个关键基因，包括Tbx5、Tbx4、Pitx1、shh、Fgf8和msx。特别是，Tbx5/4在软骨鱼中的存在强烈表明，所有具有肢体/鳍的脊椎动物都具有受Tbx基因表达调控的肢体同一性(Tamura等人，2001年)。结合MSX基因在软骨鱼中的表达模式，我们还认为软骨鱼前肢和后肢之间的侧翼区域也具有制造肢体的潜力。

1.Mechanism of regionalization of splanchnic/somatic lateral plateOur explant studies showed that the lateral plate mesoderm, which eventually is separated into splanchnic/somatic layers, has already been regionalized along the anterior-posterior axis, and they suggested that the two layers specify their antero-posterior patttern according to the regionalization (somatic makes forelimb, flank, and hindlimb, and splanchnic forms stomach, gizzard, small intestine, and large intestine).2.Specification of forelimb/hindlimb identityWe proposed a model that outset of determination to make limb identity is significantly different between forelimb and hindlimb, and that an inhibitory effect plays an important role for this determination (Saito et al., 2002). We further investigated which tissue or region involves the inhibitory factor. Somites at the wing level, implanted into leg region, inhibited the Tbx4 expression in the hindlimb region and induced the Tbx5 expression there. These results suggest that somite may be a source of the inhibitory effect that determines limb identity.3.Fin development of cartilaginous fishesWe have constructed a system to get eggs of cartilaginous fishes continually, and cloned several key genes including Tbx5, Tbx4, Pitxl, shh, fgf8 and msx from two species of cartilaginous fishes, (shark and ray). Especially, existence of Tbx5/4 in cartilaginous fishes strongly suggests that all groups of vertebrates which have limb/fin possess the limb identity regulated by Tbx gene expression (Tamura et al., 2001). Taken together with the expression pattern of msx gene in cartilaginous fishes, we also suggested that flank region between forelimb and hindlimb of cartilaginous fishes has a potential for making limb as well.