Earmuff maintains restricted potentials of mature secondary neuroblasts

描述(由申请人提供)：成人干细胞系中限制转录放大细胞增殖和抑制去分化的机制尚不清楚。果蝇幼虫脑中成熟的次级神经母细胞类似于脊椎动物的运输放大细胞，经历有限的不对称分裂来再生和产生终末分化的神经元。我们发现了一种新的转录因子Earmuff(Erm)，它可以限制成熟的次级神经母细胞的增殖并抑制其去分化。在erm突变的大脑中，成熟的次级神经母细胞去分化回其父母的神经母细胞命运，导致II型神经母细胞的急剧增加。去分化的神经母细胞的生理和功能特性与内源性的II型神经母细胞没有区别。通过在成熟的次级神经母细胞中靶向表达erm或其小鼠同源基因，可以挽救erm突变脑中的去分化表型。有趣的是，在erm突变的大脑中，成熟的次级神经母细胞的去分化与皮质细胞的极性无关。我们的数据表明，ERm通过促进细胞周期的繁荣而抑制增殖，但通过负向调节Notch信号来抑制去分化。下面概述的我们的建议将为深入了解ERM限制成熟的次级神经母细胞增殖和抑制去分化的分子机制提供依据。 与公共卫生相关：在正常发育、维持内环境稳定和组织再生期间，许多类型的干细胞会产生运输放大细胞，以瞬时扩大未分化的祖细胞池。限制细胞增殖和抑制去分化是产生必要分化后代的关键，同时防止可能导致肿瘤发生的细胞命运异常。因此，如何在转运扩增细胞中调节增殖和去分化是一个基本的问题，几乎涉及所有成体干细胞类型。在这个方案中，我们将使用发育中的苍蝇幼虫脑中成熟的次级神经母细胞作为体内模型系统来研究运输放大细胞中的增殖和去分化是如何调节的。

DESCRIPTION (provided by applicant): The mechanisms that restrict proliferation and suppress de-differentiation of transit amplifying cells in adult stem cell lineages are unknown. Mature secondary neuroblasts in Drosophila larval brains resemble vertebrate transit amplifying cells, and undergo limited rounds of asymmetric divisions to regenerate and to produce terminally differentiated neurons. We identified a novel transcription factor Earmuff (Erm), which restricts proliferation and suppresses de-differentiation of mature secondary neuroblasts. In erm mutant brains, mature secondary neuroblasts de-differentiate back into their parental neuroblast fates resulting in a dramatic increase in type II neuroblasts. The physiological and functional properties of the de-differentiated neuroblasts are indistinguishable from the endogenous type II neuroblasts. The de-differentiation phenotype in erm mutant brains can be rescued by targeted expression of Erm or its mouse homologs in mature secondary neuroblasts. Intriguingly, de-differentiation of mature secondary neuroblasts in erm mutant brains occurs independently of cortical cell polarity. Our data suggest that Erm restricts proliferation by promoting Prospero-mediate cell cycle exit, but suppresses de-differentiation by negatively regulating Notch signaling. Our proposal outlined below will provide insight into the molecular mechanisms by which Erm restricts proliferation and suppresses de-differentiation of mature secondary neuroblasts. PUBLIC HEALTH RELEVANCE: Many types of stem cells generate transit amplifying cells to transiently expand the pool of un- differentiated progenitors during normal development, maintenance of homeostasis and tissue regeneration. Restriction of proliferation and suppression of de-differentiation in transit amplifying cells are keys to generate necessary differentiated progeny while preventing aberrant cell fate specification that might lead to tumorigenesis. Thus, how proliferation and de-differentiation are regulated in transit amplifying cells is a fundamental question that concerns virtually all adult stem cell types. In this proposal, we will use mature secondary neuroblasts in developing fly larval brains as an in vivo model system to study how proliferation and de-differentiation are regulated in transit amplifying cells.