Hendriks R W, de Bruijn M F, Maas A, Dingjan G M, Karis A, Grosveld F
Department of Cell Biology and Genetics, Faculty of Medicine, Erasmus University Rotterdam, The Netherlands.
EMBO J. 1996 Sep 16;15(18):4862-72.
Bruton's tyrosine kinase (Btk) is a cytoplasmic protein kinase that is defective in X-linked agammaglobulinaemia in man and in X-linked immunodeficiency in the mouse. There is controversy regarding the stages of B cell development that are dependent on Btk function. To determine the point in B cell differentiation at which defects in Btk become apparent, we generated a mouse model by inactivating the Btk gene through an in-frame insertion of a lacZ reporter by homologous recombination in embryonic stem cells. The phenomenon of X-chromosome inactivation in Btk+/- heterozygous female mice enabled us to evaluate the competition between B cell progenitors expressing wild-type Btk and those expressing the Btk-/lacZ allele in each successive step of development. Although Btk was already expressed in pro-B cells, the first selective disadvantage only became apparent at the transition from small pre-B cells to immature B cells in the bone marrow. A second differentiation arrest was found during the maturation from IgD(low)IgM(high) to IgD(high)IgM(low) stages in the periphery. Our results show that Btk expression is essential at two distinct differentiation steps, both past the pre-B cell stage.
布鲁顿酪氨酸激酶（Btk）是一种细胞质蛋白激酶，在人类X连锁无丙种球蛋白血症和小鼠X连锁免疫缺陷中存在缺陷。关于依赖Btk功能的B细胞发育阶段存在争议。为了确定Btk缺陷在B细胞分化过程中变得明显的时间点，我们通过在胚胎干细胞中进行同源重组，将lacZ报告基因框内插入来使Btk基因失活，从而建立了一个小鼠模型。Btk+/-杂合雌性小鼠中的X染色体失活现象使我们能够评估在发育的每个连续步骤中，表达野生型Btk的B细胞祖细胞与表达Btk-/lacZ等位基因的B细胞祖细胞之间的竞争。尽管Btk在前B细胞中已经表达，但第一个选择性劣势仅在骨髓中小前B细胞向未成熟B细胞转变时才变得明显。在周围组织中从IgD（低）IgM（高）向IgD（高）IgM（低）阶段成熟的过程中发现了第二次分化停滞。我们的结果表明，Btk表达在两个不同的分化步骤中是必不可少的，这两个步骤都在pre-B细胞阶段之后。
