Sox21a promotes differentiation by enhancing the Dl/Notch signaling.

<p>(<b>A-B</b>) ISC-EB pairs in control (<i>esg</i>^<i>TS</i><i>>w</i>) and <i>Sox21a</i>-expressing (<i>esg</i>^<i>TS</i><i>>Sox21a</i>) flies. ISCs are detected with <i>Dl-GFP</i>, EBs with <i>Su(H)-lacZ</i> and progenitors with <i>esg>mCherry</i> (green). Arrows indicate ISCs in (A) and highlight the ISC-EB contact in (B). (<b>C</b>) Relative <i>Dl</i> mRNA levels in control and <i>Sox21a</i>-expressing progenitors from an RNA-seq experiment using sorted <i>esg>GFP</i>^<i>+</i> cells (n = 50 midguts/group, in two biological replicates, Robinson and Smyth Exact test, ***p < 0.001). <i>esg</i>^<i>TS</i><i>>Sox21a</i> flies were shifted to 29°C for 12 or 24 hours to induce Sox21a expression. (<b>D-E</b>) Confocal images of intestines expressing <i>Sox21a</i> alone (D) or simultaneously with a <i>Dl-RNAi</i> construct (E) using <i>esg</i>^<i>TS</i> for 36 hours. Arrows in (D) indicate some differentiating EBs, which are not present upon depleting <i>Dl</i> (E).