Stochastic mechanisms are sometimes utilized to diversify cell fates, especially in nervous systems. In the Drosophila retina, stochastic expression of the PAS-bHLH transcription factor Spineless (Ss) controls photoreceptor subtype choice. In one randomly distributed subset of R7 photoreceptors, Ss activates Rhodopsin4 (Rh4) and represses Rhodopsin3 (Rh3); counterparts lacking Ss express Rh3 and repress Rh4. In the dorsal third region of the retina, the Iroquois Complex transcription factors induce Rh3 in Rh4-expressing R7s. Here, we show that Ss levels are controlled in a binary On/Off manner throughout the retina, yet are attenuated in the dorsal third region to allow Rh3 co-expression with Rh4. Whereas the sensitivity of rh3 repression to differences in Ss levels generates stochastic and regionalized patterns, the robustness of rh4 activation ensures its stochastic expression throughout the retina. Our findings show how stochastic and regional inputs are integrated to control photoreceptor subtype specification in the Drosophila retina.

Background Esophagogastric junction outflow obstruction (EGJOO) has a variable disease course. Currently, barium swallow (BaS) and manometric parameters are used to characterize clinically significant EGJOO. The esophagogastric junction distensibility index (EGJ-DI) measured via functional lumen imaging probe (FLIP) can provide complementary information. Our aim was to assess symptom response in patients with EGJOO and an abnormal EGJ-DI after botulinum toxin (BT) treatment. Methods A prospective cohort study of adults with idiopathic EGJOO was performed from September 2019 to March 2021. Patients with dysphagia underwent upper endoscopy with FLIP. If the EGJ-DI was abnormally low, BT was injected. Data examined included demographics, medical history, endoscopic and FLIP findings, BaS, manometry, and Eckardt score (ES). ES improvement was assessed via paired samples t-test. Pearson’s chi-square tests were used to assess for associations. Results Of the 20 patients, 75% had an abnormal EGJ-DI and underwent BT injections. Mean ES for patients with abnormal EGJ-DIs significantly improved from baseline to 1, 3, and 6 month follow-up (P-values: 0.01, 0.05, and 0.02, respectively). There was a significant association between an abnormal EGJ-DI with delayed bolus transit and presence of rapid drink challenge panesophageal pressurization on manometry: P = 0.03 and P = 0.03. Conclusion This prospective study revealed that an abnormal EGJ-DI can guide BT as assessed via symptomatic response. Additionally, abnormal EGJ-DI measurements were significantly associated with other parameters used previously to determine clinically relevant EGJOO. Larger follow-up studies are warranted to further elucidate guidance for therapy in EGJOO.

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