Study on recombination signal binding protein ; RBP-Jkappa

Jkappa-RBP基因被克隆为编码与Kappa-type J片段两侧的免疫球蛋白重组信号序列(Jkappa-RS)结合的蛋白的基因。然而，该基因的表达并不局限于淋巴系统。小鼠Jkappa-RBP除了与Jkappa-RS结合外，没有发现其他功能。同时，Jkappa-RBP基因的果蝇同源物被证明是无毛抑制基因(Sup(H))，其突变会影响周围神经系统的发育，这表明Jkappa-RBP基因也参与了小鼠的神经发育。为了阐明Jkappa-RBP基因在小鼠中的功能，我们利用胚胎干细胞中的同源重组来获得该基因的零等位基因。由两个ES克隆产生的小鼠嵌合体将突变的等位基因传递给它们的后代。有一个Jkappa-RBP等位基因中断的小鼠没有表现出任何明显的异常。对Jkappa-RBP基因突变的杂合子进行杂交，以评估Jkappa-RBP基因缺失对纯合子后代的影响。新生小鼠和成年小鼠都不是纯合子，这表明胚胎阶段的纯合子致死性。胚胎的基因型分析表明，纯合子胚胎在怀孕8.5天至10.5天之间死亡。9.5d的纯合子胚胎表现为1)神经管前开口，2)不完全翻转，3)小脑。

The Jkappa-RBP gene was cloned as the gene which encodes the protein binding to the immunoglobulin recombination signal sequence flanking the kappa-type J segment (Jkappa-RS). However, expression of the gene is not restricted to the lymphoid system. And no functions of mouse Jkappa-RBP other than binding to Jkappa-RS have been found. Meanwhile, the Drosophila homologue of Jkappa-RBP gene turned out to be the gene known as Suppressor of Hairless (Sup(H)) whose mutation affects peripheral nervous system development, suggesting that the Jkappa-RBP gene is also involved in mouse neural development.To elucidate the functions of Jkappa-RBP gene in mice, we have used homologous recombination in embryonic stem (ES) cells to derive null alleles of the gene. Mouse chimeras produced from two ES clones transmitted the mutated allele to their offspring. Mice with one disrupted Jkappa-RBP allele did not show any overt abnormalities. Heterozygotes for the mutation in the Jkappa-RBP gene were intercrossed to assess the effect of the loss of Jkappa-RBP in homozygous offspring. None of the new born and adult mice were homozygotes suggesting homozygous lethality at embryonic stage. Genotype analysis of embryos shows that homozygous embryos die between day 8.5 and 10.5 of gestation. Homozygous embryos of day 9.5 show 1) anterior opening of neural tube, 2) incomplete turning, and 3) microencephaly.