GENETIC AND DYNAMIC ANALYSIS OF MURINE BONE SIZE

骨质疏松性骨折的风险是老龄化人口中的一个重要问题，不仅与骨量呈负相关，而且与骨大小呈负相关。工程学原理预测，骨大小是骨强度的重要决定因素。骨膜骨形成(PBF)是骨大小和骨强度的主要决定因素。现在有证据表明，这三种相互关联的表型都受到遗传因素的影响。我们的初步研究表明，骨大小是一种多基因遗传性状。QTL作图法是研究多基因性状的有力工具。PQCT分析显示，Rf/j和NZB/BinJ株在骨大小上相差40%，骨强度和PBF也相应地存在差异。本应用的目的是确定和阐明决定骨大小、强度和PBF的基因(S)的作用。由于候选基因的信息可以通过确定导致特定表型的机制(S)而获得，因此对于特定基因的识别非常有帮助，因此这一应用也旨在确定骨大小差异的机制基础。因此，这项申请有两套具体目标。第一套目标是：1)建立RFJ和NZB近交系小鼠骨骼大小、强度和PBF表型的最佳表达时间；2)对RF/J-NZB品系的F2代进行QTL定位，以确定同时控制股骨骨大小、骨强度和PBF的基因座；3)建立QTL与特定染色体区域的遗传连锁；以及4)产生同源品系后代，以便精细定位控制所有三种表型的主要共同QTL基因的位置。第二个具体目标将通过研究两种调节PBF的机制来确定导致同源品系小鼠骨骼更大的机制(S)：一种涉及机械拉伸的局部机制，另一种涉及涉及全身因素的全身机制，如血清胰岛素样生长因子-I。如果遗传决定的PBF变异是骨骼大小和强度的主要决定因素的假设是正确的，这项工作的遗传学方面将揭示这些同时控制PBF、骨大小和强度的基因的染色体位置，并为未来确定这些基因的身份提供框架。对同源基因小鼠进行的机制研究将为该基因控制PBF、骨骼大小和强度的机制提供重要信息。这种机制从生物学和临床角度提供了有关骨脆性的重要信息。因为大多数骨折的愈合是从骨膜开始的，所以了解PBF的过程似乎也有助于理解骨折的愈合。

The risk for osteoporotic fractures, a significant problem in the aging population, is inversely related not only to bone mass, but also to bone size. Engineering principles predict that bone size is an important determinant of bone strength. A primary determinant of bone size, and thus, bone strength, is the periosteal bone formation (PBF). There is now evidence that each of these three interrelated phenotypes are influenced by genetic factors. Our preliminary studies indicate that bone size is inherited as a polygenic trait. A powerful tool to investigate polygenic traits is the QTL mapping approach. pQCT analysis revealed that the RF/j and the NZB/BinJ strains differed by 40 percent in bone size with corresponding differences in bone strength and PBF. The goal of this application is to identify and elucidate the actions of gene(s) that determine bone size, strength and PBF. Because information about candidate genes, which may be obtained by determining the mechanism(s) leading to a given phenotype, is very helpful in identification of the specific gene, this application also intends to determine the mechanistic basis for the differences in bone size. Therefore, this application has two sets of specific aims. The first set of aims is: 1) to establish the optimum timing for expression of the bone size, strength, and PBF phenotypes in RFJ and NZB inbred strains of mice; 2) to apply QTL mapping analysis to the F2 progenies of RF/J-NZB strain pair to identify gene loci that simultaneously regulate femur bone size, bone strength, and PBF; 3) to establish genetic linkage of QTL to regions of specific chromosomes; and 4) to produce congenic strain progeny in order to fine map the location of the major common QTL genes regulating all three phenotypes. The second specific aim will determine the mechanism(s) leading to the greater bone size in the congenic strains of mice, by investigating two mechanisms which could regulate PBF: one deals with local mechanisms involving mechanical strain, and the other deals with systemic mechanisms involving systemic factors, such as serum IGF-I. If the hypothesis that genetically determined variations in PBF are a primary determinant of bone size and strength is correct, the genetic aspects of this work will reveal the chromosomal location for these genes that simultaneously control PBF, bone size and strength, and provides the framework for future work in determining the identity of these genes. The mechanistic studies with the congenic mice will yield important information on the mechanism whereby the gene understudy controls PBF, bone size and strength. Such a mechanism provides crucial information from both a biological and clinical standpoint with respect to bone fragility. Because the majority of the healing of a fracture takes place from the periosteum, it also seems likely that understanding the process of PBF could also help to understand fracture healing.