Notch pathway maintenance of the immortal germ line

虽然动物的胞体衰老并最终死亡，但生殖系通过将可遗传的信息传递给下一代而有效地保持不朽。生物体的健康完全取决于这种信息的高保真传输；因此，生殖细胞受到独特的保护，免受与衰老有关的损害。对生殖细胞的保护是在它们最初分离时授予的，通常是通过特殊细胞质的不对称遗传，并通过与性腺生态位相关联而长期保持。全面了解生态位与生殖细胞的关系将有助于阐明抑制衰老过程的机制。 我们研究的长期目标是了解参与生殖细胞生态位维持的转录网络。这项建议的目的是研究一个可能的Notch-Delta途径成员SpMibL的功能，该成员富含在紫海胆的小微体(SMM)的假定生殖细胞中。这些细胞在早期发育时被分配，并在变态过程中用于构建成年组织，包括生殖系。令人惊讶的是，如果SMM被切除，胚胎可以通过重新编程先前承诺的血统来进行补偿。我们假设SpMibL是SMM分配的上游调节因子，也是消融后重新分配新SMM的关键。SpMibL通过直接抑制SMM中的Delta配体来实现这一点，建立了分子不对称性；SMM成为缺口表达、接收细胞，而它们的邻居成为Delta表达的利基细胞。为了验证这一假设，我们将在体内击倒和过度表达SpMibL，分析产生的表型，并确定下游转录靶点。我们还将测试在SMM消融后，SpMibL和其他已知因素是否在其他谱系中被诱导。我们的结果将提供有关生殖系生态位如何维持的新的分子细节，以及生殖细胞可以从先前承诺的细胞编程。

While the soma of an animal ages and ultimately dies, the germ line remains effectively immortal by passing heritable information to the next generation. The fitness of the organism absolutely depends on the high-fidelity transmission of this information; therefore, germ cells are uniquely protected against aging-related damage. The protection of the germ cells is conferred at their initial segregation, often through the asymmetric inheritance of a specialized cytoplasm, and maintained long-term by association with a gonadal niche. A comprehensive understanding of the niche-germ cell relationship will illuminate mechanisms that suppress the aging process. The long-term goal of our research is to understand the transcriptional networks involved in germ cell-niche maintenance. The objective of this proposal is to investigate the function of a putative Notch-Delta pathway member, SpMibL, enriched in the presumptive germ cells called small micromeres (SMMs) of the sea urchin Strongylocentrotus purpuratus. These cells are allocated early in early development and are used to construct adult tissues during metamorphosis, including the germ line. Surprisingly, if the SMMs are ablated, the embryo can compensate by reprogramming previously committed lineages. We hypothesize that SpMibL is an upstream regulator of SMM allocation, and also critical for reallocating new SMMs following ablation. SpMibL achieves this by directly repressing delta ligand in the SMMs, establishing a molecular asymmetry; SMMs becoming the notch expressing, receiving cells, and their neighbors become the delta expressing, niche cells. To test this hypothesis, we will knock down and overexpress SpMibL in vivo, analyze the resulting phenotype, and identify downstream transcriptional targets. We will also test whether SpMibL, as well as other known factors are induced in other lineages following SMM ablation. Our results will provide fresh molecular detail on how the germ line niche is maintained, and germ cells can be programmed from previously committed cells.