Precisely timed regulation of enhancer activity defines the binary expression pattern of Fushi tarazu in the Drosophila embryo.

The genes that drive development each typically have many different enhancers. Properly coordinating the action of these different enhancers is crucial to correctly specifying cell-fate decisions, yet it remains poorly understood how their activity is choregraphed in time. To shed light on this question, we used recently developed single-cell live imaging tools to dissect the regulation of Fushi tarazu (Ftz) in Drosophila melanogaster embryos. Ftz is a transcription factor that is expressed in asymmetric stripes by two distinct enhancers: autoregulatory and zebra. The anterior edge of each stripe needs to be sharply defined to specify essential lineage boundaries. Here, we tracked how boundary cells commit to either a high-Ftz or low-Ftz fate by measuring Ftz protein traces in real time and simultaneously quantifying transcription from the endogenous locus and individual enhancers. This revealed that the autoregulatory enhancer does not establish this fate choice. Instead, it perpetuates the decision defined by zebra. This is contrary to the prevailing view that autoregulation drives the fate decision by causing bi-stable Ftz expression. Furthermore, we showed that the autoregulatory enhancer is not activated based on a Ftz-concentration threshold but through a timing-based mechanism. We hypothesize that this is regulated by several ubiquitously expressed pioneer-like transcription factors, which have recently been shown to act as timers in the embryo. Our work provides new insight into how precisely timed enhancer activity can directly regulate the dynamics of gene regulatory networks, which may be a general mechanism for ensuring that embryogenesis runs like clockwork.

R117H-CFTR function and response to VX-770 correlate with mRNA and protein expression in intestinal organoids.

INTRODUCTION: Variability in disease severity and CFTR modulator responses exists between patients with identical CFTR genotypes. Here, we characterized transcription, translation and function of R117H-CFTR using intestinal organoids and correlated them with in vitro responses to ivacaftor (VX-770). METHODS: Organoids were generated from individuals possessing at least one R117H-CFTR allele. The forskolin-induced swelling (FIS) assay was used to measure CFTR function and response to VX-770 treatment. R117H-CFTR protein and mRNA expression levels were determined in parallel and Pearson's correlation coefficients were assessed. RESULTS: Variability in R117H-CFTR FIS responses was observed and correlated significantly with mRNA and protein expression. Response to VX-770 treatment in organoids correlated with mRNA and protein expression as well. CONCLUSIONS: Our results indicate that gene expression, protein expression and CFTR function are strongly correlated in organoids from people with CFTR-R117H-7T/9T, which may suggest that CFTR gene expression may have consequences for CF diagnosis, prognosis and therapeutic benefit.