Molecular mechanisms of determination of limb region and identity

点击翻译按钮获取中文摘要

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.