Temporal regulation of C. elegans metabolic gene expression by the heterochronic protein LIN-29 at the larval to adult transition

项目摘要 在动物和人类的发育过程中，单细胞胚胎分裂产生所有的细胞类型， 在成人中。为了使这一过程正确发生，储存在每个细胞基因组中的遗传信息 必须在正确的时间，在正确的细胞中表达，当这些事件没有正确发生时， 发育异常和出生缺陷。虽然对空间控制的了解很多， 在后生动物的基因表达中，关于基因表达的时间控制以及如何控制基因表达， 在动物发育过程中，事件在时间上是协调的。在线虫C. elegans，a pathway途径 被称为“异时途径”的基因和microRNA已经被表征为控制着 幼虫生活中的发育事件。这一通路的末端成分是锌指 转录因子LIN-29，它调节从幼虫晚期到 成虫期（L/A过渡）在表皮和其他蠕虫组织。LIN-29的几个直接目标是已知的： 最具特征的是在L/A转换处表达的基因，该基因编码角质层胶原蛋白， 由表皮细胞分泌的蠕虫外壳的组成部分。为了理解时间 发育转变的调节LIN-29调节基因通过时间错配鉴定， 在较早的发育时间表达LIN-29并分析基因表达。该RNA-Seq 分析鉴定了232个被LIN-29上调的基因，其中许多编码角质层胶原蛋白（33/232）， 和/或在L4/A转换前显示正常表达峰（63/232）。分析还发现， 352个基因在LIN-29不适当的早期表达后下调。最为显著 在下调的基因列表中，有一大类基因与脂肪酸代谢有关， 在蠕虫肠道中表达的代谢，其基因产物是蛋白质-蛋白质的一部分 相互作用网络在人类中保存。此外，在成年期LIN-29的暂时性错误表达 导致寿命显著缩短。这些结果和其他结果表明，LIN-29调节了一种新的免疫调节因子。 从表皮移动到肠的信号，其接收导致转录 一组脂肪酸代谢基因的下调，使蠕虫的代谢从 从满足幼虫的需要（快速生长）到满足成虫的需要（寿命长，卵黄发生）。 将进行实验来检验这一假设，并具体识别信号的性质。 以及介导这种组织间通讯的转录因子。工作的完成 本文提出的方法将对我们理解基因表达的时间调控产生重大影响 在一个模型后生动物，并揭示了新的光控制代谢过程中的发展过渡。 由于LIN-29的同源物及其推定的靶点在人类中是保守的，因此所获得的知识将 与我们对人类正常发育、健康和衰老的理解有关。

Project Summary During animal and human development, the single-cell embryo divides to generate all of the cell types found in the adult. For this process to occur correctly, the genetic information stored in the genome of every cell must be expressed in the right cells and at the right time, and when these events do not occur correctly developmental anomalies and birth defects can occur. While much is known about the spatial control of gene expression in metazoans, less is known about the temporal control of gene expression and how events are coordinated in time during animal development. In the nematode worm C. elegans, a pathway of genes and microRNAs called the ‘heterochronic pathway’ has been characterized that controls the timing of developmental events during larval life. The terminal component of this pathway is the zinc finger transcription factor LIN-29, which regulates the important developmental transition from late larval life to adulthood (L/A transition) in the epidermis and other worm tissues. Few direct targets of LIN-29 are known: the best characterized is a gene expressed at the L/A transition which encodes a cuticle collagen, the major component of the outer covering of the worm secreted by the epidermal cells. To understand the temporal regulation of developmental transitions LIN-29 regulated genes were identified by temporally mis- expressing LIN-29 at an earlier developmental time and analyzing gene expression. This RNA-Seq analysis identified 232 genes upregulated by LIN-29, many of which encode cuticle collagens (33/232), and/or show a normal peak of expression before the L4/A transition (63/232). This analysis also identified 352 genes down-regulated upon inappropriate early expression of LIN-29. The most significantly overrepresented category of genes on the down-regulated list are a large group involved in fatty acid metabolism that are expressed in the worm intestine, and whose gene products are part of a protein-protein interaction network conserved in humans. In addition, temporal mis-expression of LIN-29 during adulthood leads to a significant shortening of lifespan. These results and others suggest that LIN-29 regulates a signal that moves from the epidermis to the intestine, the reception of which results in the transcriptional down-regulation of a set of fatty acid metabolic genes which shifts the metabolism of the worm from that meeting the needs of the larva (rapid growth) to that meeting the needs of the adult (long life, vitellogenesis). Experiments to test this hypothesis will be performed, and to specifically identify the nature of the signal(s) and the transcription factor(s) mediating this inter-tissue communication. The accomplishment of the work proposed here will have a significant impact on our understanding of temporal regulation of gene expression in a model metazoan, and shed new light on the control of metabolism during developmental transitions. Because homologs of LIN-29 and its putative targets are conserved in humans, the knowledge gained will have relevance to our understanding of normal human development, health and aging.