Neural Lineage Progression Controlled by a Temporal Proliferation Program. Drosophila melanogaster

Great progress has been made in identifying transcriptional programs that establish stem cell identity. In contrast, we have limited insight into how these programs are down-graded in a timely manner to halt proliferation and allow for cellular differentiation. Drosophila embryonic neuroblasts undergo such a temporal progression, initially dividing to bud off daughters that divide once (type I), then switching to generating non-dividing daughters (type 0), and finally exiting the cell cycle. We identify six early transcription factors that drive neuroblast and type I daughter proliferation. Early factors are gradually replaced by three late factors, acting to trigger the type I->0 daughter proliferation switch and eventually to stop neuroblasts. Early and late factors regulate each other and four key cell cycle genes, providing a logical genetic pathway for these transitions. The identification of this extensive driver-stopper temporal program controlling neuroblast lineage progression may have implications for studies in many other systems. Overall design: We generated two quadruple transgenic UAS combinations: UAS-ase, -SoxN, -wor, -Kr (denoted UAS-Quad), and dominant-negative or -activated versions of three of the same of genes, UAS-ase-Vp16, -SoxN-EnR, -wor-EnR, with UAS-Kr encoding a wild type protein (denoted UAS-QuadD). UAS-Quad and UAS-QuadD misexpression were driven from da-Gal4. To analyze the transcriptomic effects of the Quad and QuadD misexpression, we conducted RNAseq analysis for two separate set of experiments: 1) da-Gal4/+ (control) VS da-Gal4/UAS-Quad), and 2) da-Gal4/+ (control) VS da-Gall4/UAS-QuadD. Within each experiment, we generated two biological replicates per genotype (control and gain-of-function). In total, we thus analyzed 8 samples (4 per each experiment; two replicates for control and two replicates for gain-of-function).