Distinct gene-selective roles for a network of core promoter factors in Drosophila neural stem cell identity.

Abstract

The transcriptional mechanisms that allow neural stem cells (NSC) to balance self-renewal with differentiation are not well understood. Employing an in vivo RNAi screen we identify here NSC-TAFs, a subset of nine TATA-binding protein associated factors (TAFs), as NSC identity genes in Drosophila. We found that depletion of NSC-TAFs results in decreased NSC clone size, reduced proliferation, defective cell polarity and increased hypersensitivity to cell cycle perturbation, without affecting NSC survival. Integrated gene expression and genomic binding analyses revealed that NSC-TAFs function with both TBP and TRF2, and that NSC-TAF-TBP and NSC-TAF-TRF2 shared target genes encode different subsets of transcription factors and RNA-binding proteins with established or emerging roles in NSC identity and brain development. Taken together, our results demonstrate that core promoter factors are selectively required for NSC identity in vivo by promoting cell cycle progression and NSC cell polarity as well as by restraining premature differentiation. Because pathogenic variants in a subset of TAFs have all been linked to human neurological disorders, this work may stimulate and inform future animal models of TAF-linked neurological disorders.\n\nAuthor summaryThe brains of many animal species are built with brain stem cells. Having too many brain stem cells can lead to brain tumors whereas too few can lead to birth defects such as microcephaly. A number of next generation sequencing studies have implicated proteins referred to as TATA-box-binding protein associated factors (TAFs) in human neurological disorders including microcephaly, but prior to this study, their function in brain development was unknown. Here we use brain stem cells, known as neural stem cells (NSCs), from the fruit fly Drosophila melanogaster as a model system to decipher how TAFs control brain stem cell identity. By combining genetics and low-input genomics, we show that TAFs directly control NSC cell division and cell polarity but do not appear to be required for NSC survival. We further show that TAFs accomplish these functions by associating either with their canonical partner TBP (TATA-binding protein) or the related protein TRF2. In summary, our study reveals unexpected and gene-selective functions of a unique subset of TAFs and their binding partners, which could inform future studies that seek to model human neurological disorders associated with TAFs.