Joint Study on Inductive Interactions in Development

在这项研究中，我们研究了细胞-细胞黏附在发育诱导过程中的作用。此前，Yuge博士发现青蛙胚胎16-细胞期背部卵裂球的细胞质具有背部决定活性。Gumbiner教授和Brieher博士阐明了β-连环素在青蛙背腹轴形成中的重要性，Gerhart教授的研究小组展示了β-连环素作为背部决定因素的重要性。Yuge博士检查了他的背部决定因素是否是β-连环素，并发现他的决定因素与β-连环素不同。他的决定因素和β-连环素定位于分裂胚胎的皮质，Kageura博士表明，皮质移植导致次级轴形成的频率非常高。钙粘附素是钙依赖的细胞-细胞黏附分子，似乎通过吸收游离的β-连环素间接控制轴向诱导。为了阐明钙粘附素在诱导中的作用，Tajima克隆了XB钙粘附素基因，并构建了两种不同的显性负性基因结构。敲除钙粘蛋白基因产物对青蛙胚胎原肠发育的影响最小，而对细胞间黏附的影响最小。这有力地表明，其他黏附分子在早期胚胎发生中也是活跃的。野村证券发现了一种新的人B血型活性糖基磷脂酰肌醇锚定凝集素(PI-lectin)，这种凝集素对钙依赖的细胞-细胞黏附是必不可少的。这些蛋白质是可溶性青蛙皮质颗粒凝集素的膜锚定同系物，定位于未受精卵的皮质，在受精时起到阻止多精受精的作用。因此，新发现的PI-凝集素似乎在早期胚胎粘连中发挥了重要作用，它们的定位强烈表明它与背轴决定因素相互作用。PI-凝集素的敲除工作正在我们实验室进行。

In this study, we examined the roles of cell-cell adhesion in inductive processes in development. Previously, Dr.Yuge discovered that the cytoplasm of 16-cell stage dorsal blastomeres of frog embryos has dorsal determinant activity. Prof.Gumbiner and Dr.Brieher clarified the importance of beta-catenin in frog dorsoventral axis formation, and Prof.Gerhart's group showed the importance of beta-catenin as dorsal determinant. Dr.Yuge examined whether his dorsal determinants are beta-catenins or not, and found that his determinants are different from beta-catenins. His determinants and beta-catenins are localized in the cortex of the cleaving embryos, and Dr.Kageura showed that grafting of cortex causes secondary axis formation at a very high frequency. Cadherins that are Ca^<2+> dependent cell-cell adhesion molecules seem to be controlling axis induction indirectly by absorbing free beta-catenins. To clarify the roles of cadherins in induction, Tajima cloned the XB cadherin cDNA and made two different dominant negative gene constructs. Gastrulation of frog embryos was affected by knocking out of cadherin gene products while cell-cell adhesion is least affected. This strongly suggests that other adhesion molecules are active in early embyogenesis. Nomura identified novel human blood group B active glycosylphosphatidyl inositol anchored lectin (Pi-lectin), which are essential for Ca^<2+> dependent cell-cell adhesion. The proteins are membrane anchored homologues of soluble frog cortical granule lectins which are localized in cortex of the unfertilized egg and act for blocking of polyspermy at fertilization. Thus newly discovered Pi-lectin seems to be playing major roles in early embryonic adhesion, and their localization strongly suggests that it is interacting with dorsal axis determinants. The knocking out of the Pi-lectin is being carried out in our laboratory.