Identification of a chromosomal region that is responsible for memory T cell homeostasis in a mutant mouse.

众所周知，与初始T细胞相比，记忆T细胞增殖更快，对病原体的反应更强。我在美国丹佛国家犹太医学中心的SPF群体中发现了一只携带过量CD 4+和CD 8+记忆T细胞的雌性突变小鼠，其表型以常染色体隐性庄园遗传。细胞大小较小（约为对照的10%），双阳性细胞数量显著减少。T细胞分化在前TCR信号传导是必需的步骤（称为DN 3）被部分但主要地阻断。血清中血小板显著增加，这一结果与脾脏中巨核细胞过量一致。此外，未成熟B细胞的数量显著减少，并且B细胞的分化在大的前B阶段被阻断，其中前BCR信号传导是重要的。我进行了骨髓移植实验，以分析淋巴祖细胞的突变或微环境的突变是否是突变小鼠T和B细胞表型所必需的。淋巴祖细胞本身的突变是观察表型所必需的。为了鉴定携带引起突变小鼠表型的责任基因的DNA片段，我们采用SSPL方法。我们将B10#4小鼠与NZB小鼠杂交，获得F2小鼠，并获得100多个表型+和-后代。我们在第2号染色体上发现了一个1cM的DNA片段，根据NCBI数据库，该片段含有约40个基因。对该片段中一个基因的RT-PCR实验结果令人着迷，因为该基因的剪接模式在B10#4和对照小鼠之间是不同的。我分析了该基因的序列，发现该基因的内含子中有两个突变。

It is well known that memory T cells proliferate faster and react to the pathogens stronger compared to naive T cells. I found a female mutant mouse carrying excess amount of memory T cells of both CD4+ and CD8+ in a SPF colony in National Jewish Medical Center, Denver, CO. The phenotype is inherited as an autosomal recessive manor. Thymus size is small (about 10% of controls) and the numbers of double positive cells reduces dramatically. T cell differentiation is partially but dominantly blocked at a step where preTCR signaling is necessary named DN3. Platelets significantly increased in serum and this result is consistent with excess amount of megakaryocytes in spleen. In addition, the number of immature B cells decreased significantly and differentiation of B cells is blocked at large preB stage where preBCR signaling is important. I performed bone marrow transplantation experiment to analyze if the mutation in lymphoid progenitor is or if it in microenvironment is necessary for the phenotype of T and B cells in the mutant mice. The mutation in lymphoid progenitor cells themselves is necessary to see the phenotype. In order to identify a DNA fragment carrying a responsible gene that induces the phenotype in the mutant mice, we employed SSPL method. We crossed B10#4 mice with NZB mice to get F2 mice and got over 100 phenotype + and -offspring. We identified 1cM DNA fragment in chromosome #2 that is responsible for the mutant and the fragment has about 40 genes according to NCBI database. Result of RT-PCR experiment for a gene in the fragment was fascinating, since splicing pattern of the gene is different between the B10#4 and control mice. I analyzed sequence of the gene and found that there were two mutations in the introns of the gene.