Biochemistry, Cell & Molecular Biology Program, Central Michigan University, Mt Pleasant, Michigan, United States of America.
Department of Biology, Central Michigan University, Mt Pleasant, Michigan, United States of America.
PLoS Genet. 2021 Nov 15;17(11):e1009881. doi: 10.1371/journal.pgen.1009881. eCollection 2021 Nov.
Many tissue-specific stem cells maintain the ability to produce multiple cell types during long periods of non-division, or quiescence. FOXO transcription factors promote quiescence and stem cell maintenance, but the mechanisms by which FOXO proteins promote multipotency during quiescence are still emerging. The single FOXO ortholog in C. elegans, daf-16, promotes entry into a quiescent and stress-resistant larval stage called dauer in response to adverse environmental cues. During dauer, stem and progenitor cells maintain or re-establish multipotency to allow normal development to resume after dauer. We find that during dauer, daf-16/FOXO prevents epidermal stem cells (seam cells) from prematurely adopting differentiated, adult characteristics. In particular, dauer larvae that lack daf-16 misexpress collagens that are normally adult-enriched. Using col-19p::gfp as an adult cell fate marker, we find that all major daf-16 isoforms contribute to opposing col-19p::gfp expression during dauer. By contrast, daf-16(0) larvae that undergo non-dauer development do not misexpress col-19p::gfp. Adult cell fate and the timing of col-19p::gfp expression are regulated by the heterochronic gene network, including lin-41 and lin-29. lin-41 encodes an RNA-binding protein orthologous to LIN41/TRIM71 in mammals, and lin-29 encodes a conserved zinc finger transcription factor. In non-dauer development, lin-41 opposes adult cell fate by inhibiting the translation of lin-29, which directly activates col-19 transcription and promotes adult cell fate. We find that during dauer, lin-41 blocks col-19p::gfp expression, but surprisingly, lin-29 is not required in this context. Additionally, daf-16 promotes the expression of lin-41 in dauer larvae. The col-19p::gfp misexpression phenotype observed in dauer larvae with reduced daf-16 requires the downregulation of lin-41, but does not require lin-29. Taken together, this work demonstrates a novel role for daf-16/FOXO as a heterochronic gene that promotes expression of lin-41/TRIM71 to contribute to multipotent cell fate in a quiescent stem cell model.
许多组织特异性干细胞在长时间不分裂或静止期保持产生多种细胞类型的能力。FOXO 转录因子促进静止和干细胞维持，但 FOXO 蛋白在静止期促进多能性的机制仍在不断出现。秀丽隐杆线虫中的单个 FOXO 直系同源物，daf-16，在响应不利的环境线索时，促进进入一种静止和抗应激的幼虫阶段，称为 dauer。在 dauer 期间，干细胞和祖细胞保持或重新建立多能性，以使 dauer 后正常发育能够恢复。我们发现，在 dauer 期间，daf-16/FOXO 阻止表皮干细胞（ seam 细胞）过早地采用分化的、成年特征。具体来说，缺乏 daf-16 的 dauer 幼虫错误表达正常成年富集的胶原蛋白。使用 col-19p::gfp 作为成年细胞命运标记，我们发现所有主要的 daf-16 同工型都有助于在 dauer 期间拮抗 col-19p::gfp 的表达。相比之下，经历非 dauer 发育的 daf-16(0)幼虫不会错误表达 col-19p::gfp。成年细胞命运和 col-19p::gfp 表达的时间由包括 lin-41 和 lin-29 在内的异时基因网络调节。lin-41 编码一种 RNA 结合蛋白，与哺乳动物中的 LIN41/TRIM71 同源，lin-29 编码一种保守的锌指转录因子。在非 dauer 发育过程中，lin-41 通过抑制 lin-29 的翻译来拮抗成年细胞命运，lin-29 直接激活 col-19 转录并促进成年细胞命运。我们发现，在 dauer 期间，lin-41 阻断 col-19p::gfp 的表达，但令人惊讶的是，lin-29 在这种情况下不是必需的。此外，daf-16 在 dauer 幼虫中促进 lin-41 的表达。在 daf-16 减少的 dauer 幼虫中观察到的 col-19p::gfp 错误表达表型需要 lin-41 的下调，但不需要 lin-29。总之，这项工作证明了 daf-16/FOXO 作为一种异时基因的新作用，促进 lin-41/TRIM71 的表达，以促进静止期干细胞模型中的多能细胞命运。
