Elucidating the function of the transcription factor Bhlhe41 during B-1a cell development and in imprinting of B-1a cell self-renewal properties

B-1a细胞是先天样B淋巴细胞的一个亚群，其可在遇到病原体时有助于第一道防线以及清除细胞碎片以维持组织稳态。B-1a细胞主要在胎儿和新生儿期间产生，并且不太有效地由成人骨髓补充，因此它们通过自我更新在生物体的整个生命周期中保持其数量。虽然细胞因子受体信号传导和某些代谢要求与B-1a细胞自我更新有关，但B-1a细胞自我更新能力的精确分子机制仍然难以捉摸。此外，虽然B细胞受体信号传导的指导性作用已经涉及向B-1a细胞谱系的转移，但B-1a细胞发育仍然知之甚少。 最近，转录因子Bhlhe 41被鉴定为B-1a细胞发育和自我更新的关键调节因子。已发表的关于Bhlhe 41生殖系缺陷小鼠的结果表明，Bhlhe 41在B-1a细胞中起着两种时间上不同的作用-首先在个体发育早期控制它们的发育，然后调节成熟B-1a细胞独特的自我更新特性。然而，我们通过在早期和晚期B-1a细胞发育过程中条件性缺失Bhlhe 41获得的初步数据挑战了这一模型，并表明Bhlhe 41可能在成熟B-1a细胞中大量缺失。此外，这些结果还表明，成熟B-1a细胞的独特自我更新特性在B-1a细胞分化早期的狭窄时间窗内被Bhlhe 41“印记”。因此，本研究的最终目的是阐明Bhlhe 41在B-1a细胞发育过程中的功能以及在B-1a细胞自我更新特性的印记中的作用。为了实现这一目标，我将追求以下具体目标：首先，我将彻底表征B-1a细胞发育早期和晚期条件性缺失Bhlhe 41后的B-1a细胞区室。第二，我将破译Bhlhe 41在早期B-1a淋巴细胞生成中的细胞和分子功能，以及在Raidsky教授实验室最近开发的诱导B-1a细胞分化系统中的功能。最后，作为一个额外的方向，我也将致力于使用Bhlhe 41作为分子标记，以确定迄今为止难以捉摸的人类B 1a细胞群体。 总之，在这个研究项目中获得的结果不仅对促进我们对小鼠和人类体液免疫系统的理解有价值，而且还为自我更新的分子机制提供了重要的见解。

B-1a cells are a subset of innate-like B lymphocytes which can contribute to the first line of defense upon pathogen encounter as well as to clearing cellular debris to maintain tissue homeostasis. B-1a cells are primarily generated during fetal and neonatal life and are less efficiently replenished by adult bone marrow, and therefore they maintain their numbers throughout the lifetime of an organism by self-renewal. Although cytokine receptor signaling and certain metabolic requirements are pertinent to B-1a cell self-renewal, the precise molecular mechanisms underlying the ability of B-1a cells to self-renew remain elusive. Moreover, while an instructive role of B cell receptor signaling has been implicated in the diversion toward the B-1a cell lineage, B-1a cell development is still poorly understood. Recently, the transcription factor Bhlhe41 was identified as a key regulator of B-1a cell development and self-renewal. Published results obtained with Bhlhe41 germline-deficient mice suggested that Bhlhe41 plays two temporally distinct roles in B-1a cells – first controlling their development early in ontogeny and later regulating the unique self-renewal properties of mature B-1a cells. However, our preliminary data obtained by conditional deletion of Bhlhe41 during early and late B-1a cell development challenge this model and indicate that Bhlhe41 may be largely dispensable in mature B-1a cells. Moreover, these results also suggest that the unique self-renewal properties of mature B-1a cells are ‘imprinted’ by Bhlhe41 in a narrow time window early in B-1a cell differentiation. Therefore, the ultimate goal of this research project is to elucidate the function of Bhlhe41 during B-1a cell development and in imprinting of B-1a cell self-renewal properties. To accomplish this goal, I will pursue the following specific aims: First, I will thoroughly characterize the B-1a cell compartment upon conditional deletion of Bhlhe41 early and late in B-1a cell development. Second, I will decipher the cellular and molecular function of Bhlhe41 during early B-1a lymphopoiesis, as well as in a system of inducible B-1a cell differentiation recently developed by Prof. Rajewsky’s lab. Finally, as an additional direction, I will also aim to use Bhlhe41 as a molecular marker to identify a so far elusive population of human B 1a cells. Together, the results obtained within this research project will not only be valuable in advancing our understanding of the humoral immune system of mice and men, but also provide significant insights into molecular mechanisms of self-renewal.