Congenic Mice Provide Evidence for a Genetic Locus That Modulates Spontaneous Arthritis Caused by Deficiency of IL-1RA

To understand the role of genetic factors involved in the development of spontaneous arthritis in mice deficient in IL-1 receptor antagonist protein (IL_1RA), we have identified a genomic region containing a major quantitative trait locus (QTL) for this disease. The QTL is on chromosome 1 and appears to be the strongest genetic region regulating arthritis. To confirm the importance of the QTL and to identify potential candidate genes within it, we conducted speed congenic breeding to transfer the QTL region from DBA/1 mice that are resistant to spontaneous arthritis into BALB/c−/− which are susceptible. Genetic markers along every chromosome were used to assist in the selection of progeny in each generation to backcross to BALB/c−/−. By the 6th generation we determined that all of the chromosomes in the progeny were of BALB/c origin with the exception of portions of chromosome 1. At this stage we intercrossed selected mice to produce homozygous strains containing the genomic background of BALB/c−/− except for the QTL region on chromosome 1, which was from DBA/1. We were able to establish two congenic strains with overlapping DBA/1 DNA segments. These strains were observed for the development of spontaneous arthritis. Both congenic strains were relatively resistant to spontaneous arthritis and had delayed onset and reduced severity of disease. The gene/s that regulates this major QTL would appear to be located in the region of the QTL that is shared by both strains. The common transferred region is between D1Mit110 and D1Mit209 on chromosome 1. We evaluated this region for candidate genes and have identified a limited number of candidates. Confirmation of the identity and precise role of the candidates will require additional study.为阐明白细胞介素1受体拮抗剂蛋白（IL-1 receptor antagonist protein, IL-1RA）缺陷小鼠自发性关节炎发病过程中的遗传调控作用，我们成功定位到一个与该疾病相关的主效定量性状位点（quantitative trait locus, QTL）所在的基因组区域。该QTL位于1号染色体，是调控该自发性关节炎的最强效遗传区域。为验证该QTL的生物学功能并定位其内部潜在候选基因，我们采用速度同类系繁育技术，将抗自发性关节炎的DBA/1小鼠的QTL区域，转移至易感该疾病的BALB/c-/-小鼠基因组中。实验过程中，我们利用全染色体遗传标记辅助筛选每一代子代，并将子代回交于BALB/c-/-小鼠。至第6代时，我们确认子代小鼠的所有染色体均为BALB/c遗传背景，仅1号染色体存在片段差异。在此阶段，我们对筛选获得的小鼠进行互交，成功构建纯合品系：该品系的基因组背景与BALB/c-/-一致，仅1号染色体上的QTL区域来源于DBA/1小鼠。我们最终获得两个携带重叠DBA/1 DNA片段的同类系品系，随后观察了这两个品系的自发性关节炎发病情况。结果显示，两个同类系品系均对自发性关节炎呈现相对抗性，表现为发病延迟、疾病严重程度降低。调控该主效QTL的功能基因应位于两个品系共享的导入区域内。该共同导入区域位于1号染色体上D1Mit110与D1Mit209分子标记之间。我们对该区域进行了候选基因筛选，仅获得少量候选基因。验证这些候选基因的身份及其确切生物学功能仍需开展进一步研究。