Developmental Mechanisms for the Evolution of Bone Loss

描述(由申请人提供)：包括骨质疏松症在内的骨丢失疾病是美国老龄化人口面临的一个重大且日益严重的威胁。退行性骨量减少是一个复杂的特征，包括环境和遗传因素，可能是由于自然选择的强度降低，以维持生殖后个体强劲的骨生产。这一复杂特征的自然变异存在于某些脊椎动物谱系中，导致继发性骨量减少症的适应性进化。我们将人类疾病进化突变模型的创新策略应用于南极鱼类的骨骼，这些鱼类的祖先拥有健壮的骨骼。随着对密集骨骼的自然选择在某些南极鱼类谱系中的减少，骨骼变得嗜骨性，使动物能够生活在水柱中并利用其丰富的资源。保留密集骨骼的相关血统继续在海底觅食。这项拟议工作的目标是表征骨质疏松症和正常骨骼物种之间的遗传和表型差异，从而确定新的人类骨骼退行性疾病的候选基因和机制。我们的假设是，无论是下调正向调控成骨的基因活性的突变，还是上调负面影响成骨的基因活性的突变，都是骨质疏松症与骨骼健壮的相关物种进化差异的原因。目的1通过软骨、骨和细胞外基质分子的染色以及骨骼标记基因的表达，鉴定骨量稀少的刺头鱼(黑鳍冰鱼)和相关的强壮的骨化物种角鱼(黄腹鳕鱼)之间骨骼发育的不同阶段。目的2将使用高通量的cDNA测序来比较骨化程度高和骨化程度低的物种的骨骼组织的基因表达谱，以此来识别这两个物种之间的调控差异。目的3通过三刺鱼的功能丧失和功能获得实验，确定骨骼调节基因在骨化骨骼发育中的功能作用。刺鱼是一种与我们的南极鱼类有亲缘关系的模式物种，拥有完全测序的基因组，并且可以在实验室中进行基因敲除和转基因。 意义：这些实验将揭示基因的身份和功能，这些基因的活性在自然选择的压力下发生了变化，以减少南极鱼类的骨骼骨化。由于骨矿化随进化时间的减少与人类骨丢失疾病随发育时间的变化相似，这些研究有可能识别新的基因，并为骨量减少、骨质疏松症和其他骨损耗疾病的机制提供新的见解，可以利用这些机制来开发治疗人类疾病的新方法。 项目简介：拟议的实验将揭示基因的身份和功能，这些基因的活动在自然选择的压力下发生了变化，导致某些南极鱼类谱系的骨密度下降。由于南极鱼类随进化时间的骨矿化减少模拟了人类随着年龄的增长而随着发育时间的推移骨密度的降低，拟议的研究有可能识别新的基因，并为低骨矿密度、骨质疏松症和其他骨损耗疾病的机制提供新的见解，这些机制可以被用来开发治疗人类疾病的新疗法。

DESCRIPTION (provided by applicant): Bone loss diseases, including osteoporosis, are a significant and increasing threat for America's aging population. Degenerative osteopenia is a complex trait with environmental and genetic components, and may have arisen from a reduction in the strength of natural selection to maintain robust bone production in post- reproductive individuals. Natural variation for this complex trait exists in certain vertebrate lineages leading to the adaptive evolution of secondary osteopenia. We apply the innovative strategy of evolutionary mutant models for human disease to the skeletons of osteopenic Antarctic fish, whose ancestors possessed robust skeletons. As natural selection for dense bones diminished in certain lineages of Antarctic fish, the skeleton became osteopenic, allowing animals to inhabit the water column and exploit its abundant resources. Related lineages that retain dense skeletons continue to forage on the ocean floor. The goal of the proposed work is to characterize the genetic and phenotypic differences between species with osteopenic and normal skeletons, and thereby identify new candidate genes and mechanisms for human bone degeneration diseases. Our hypothesis is that mutations that either down-regulate the activity of genes that positively regulate osteogenesis or up-regulate the activity of genes that negatively affect osteogenesis account for evolved differences in related species with osteopenic versus robust skeletons. Aim 1 will identify the stages at which skeletal development diverges between the osteopenic species Chaenocephalus aceratus (blackfin ice fish) and the related robustly ossified species Notothenia coriiceps (yellowbelly rock cod) using stains for cartilage, bone, and extracellular matrix molecules, and the expression of skeletal marker genes. Aim 2 will use high- throughput cDNA sequencing to compare gene expression profiles of skeletogenic tissues from densely and poorly ossified species as a means to identify regulatory differences between the two species. Aim 3 will define the functional roles of skeletal regulatory genes in the development of the ossified skeleton using loss- of-function and gain-of-function experiments in three-spine stickleback. Stickleback, a model species related to our Antarctic fish, has a completely sequenced genome, and is amenable to gene knockdown and transgenesis in the laboratory. Significance: These experiments will reveal the identities and functions of genes whose activities have changed, under the force of natural selection, to reduce skeletal ossification in Antarctic fish. Because the reduction of bone mineralization over evolutionary time mimics human bone loss diseases over developmental time, these studies have the potential to identify new genes, and provide new insights into mechanisms for osteopenia, osteoporosis, and other bone wasting disorders that can be exploited to develop novel therapies for human disease. Project Narrative: The proposed experiments will reveal the identities and functions of genes whose activities have changed, under the force of natural selection, leading to loss of bone mineral density in certain lineages of Antarctic fish. Because the reduction of bone mineralization over evolutionary time in Antarctic fish mimics the reduction of bone density in humans as they age over developmental time, the proposed studies have the potential to identify new genes, and provide new insights into mechanisms for low bone mineral density, osteoporosis, and other bone wasting disorders that can be exploited to develop novel therapies for human disease.