SPARC as an essential regulator of fat body development and maintenance critical for Drosophila melanogaster larval progression

多细胞生物的出现与编码细胞外基质(ECM)分子的基因的出现是一致的，细胞外基质分子产生了两种不同的ECM：间质基质和基膜/基膜。BL在多细胞生物体中高度保守，位于上皮细胞和内皮细胞之下，包裹着组织和器官以及神经、肌肉纤维和脂肪细胞。除了提供机械支持和作为细胞迁移和存活的粘附性底物外，BL还通过与多种跨膜受体、生长因子和细胞因子的相互作用对生物体的发育做出关键贡献。BLS的基本成分包括形成网络的IV型胶原(ColIV)、层粘连蛋白(Lm)、Perlecan和Nidogen，它们通过复杂但仍鲜为人知的过程组装成片状网络。本申请中概述的研究计划的目标是定义以黑腹果蝇为模型的编排BL组装的关键组件。我们已经证明，SPARC(分泌性蛋白，酸性，富含半胱氨酸)是一种结合钙和胶原的基质细胞扩散糖蛋白，是果蝇胚胎BL的主要成分。我们最近的数据表明，SPARC缺乏导致幼虫死亡与脂肪体BL的早熟重构有关。胚胎和幼虫的脂肪体对于苍蝇的发育是必不可少的，这些脂肪具有储存营养和调节能量供应的功能。脂肪体主要是由脂肪细胞组成的，它们各自被包裹在层状结构中，类似于脊椎动物的脂肪细胞。SPARC的缺失导致圆形脂肪体脂肪细胞周围聚集了不正确组装的BL成分和早熟摄食行为。克隆分析表明，BL组分的积累是细胞自主的。在本地SPARC启动子和将SPARC表达限制在脂肪体的驱动系的控制下，通过表达SPARC的基因组构建物拯救了幼虫的致死性。基于这些发现，我们假设SPARC通过与CoIIV的钙依赖相互作用，促进了BL周围脂肪细胞的适当片状组装。SPARC的缺失会导致BL的异常形成和积累，导致脂肪体的重塑，从而导致幼虫死亡。

The emergence of multicellular organisms was co-incident with the appearance of genes coding for extracellular matrix (ECM) molecules that gave rise to two distinct ECMs, interstitial matrices and basal laminae (BL)/basement membranes. BL, which are highly conserved in multicellular organisms, underlie epithelial and endothelial cells and envelop tissues and organs as well as nerves, muscle fibers and adipocytes. In addition to providing mechanical support and serving as an adhesive substrata for cell migration and survival, BL make critical contributions to the development of organisms via interactions with a diverse number of transmembrane receptors, growth factors and cytokines. The basic components of BLs include network-forming Collagen IV (ColIV), Laminin (LM), Perlecan, and Nidogen, which are assembled into sheet-like networks through complex and still poorly understood processes. The goal of the research program outlined in this application is to define key components that orchestrate BL assembly using Drosophila melanogaster as a model. We have shown that SPARC (Secreted Protein, Acidic, Rich in Cysteine), a Ca2+- and collagen-binding matricellular diffusible glycoprotein, is a major component of Drosophila embryonic BL. Our recent data indicate that SPARC deficiency leads to larval lethality associated with precocious remodelling of fat body BL. The embryonic and larval fat body is essential to fly development that functions nutrient storage and regulation of energy availability. The fat body is largely composed of adipocytes, individually enveloped within a BL, similar to adipocytes within vertebrates. Loss of SPARC results in rounded fat body adipocytes surrounded with an accumulation of improperly assembly BL components and precocious feeding behavior. Clonal analyses revealed that the accumulation of BL components was cell autonomous. Larval lethality was rescued with a genomic construct expressing SPARC under the control of the native SPARC promoter and driver lines restricting SPARC expression to the fat body. Based on these findings, we hypothesize that SPARC, via Ca2+-dependent interactions with CoIIV, promotes the proper sheet-like assembly of BL surrounding adipocytes. Loss of SPARC results in the aberrant formation and accumulation of BL, leading to remodeling of the fat body that results in larval lethality.