Dpp-spalt Signaling Regulates Cell Morphogenesis In Drosophila Wing Disc

Drosophila wing imaginal disc is a sac-like structure composed of two opposing cell layers, peripodial epithelium (PE, also known as squamous epithelia) and disc proper (DP, also known as pseudostratified columnar epithelia). The molecular mechanism of cell morphogenesis in DP but not PE has been well studied.Previous studies have shown that Dpp signaling is essential for the correct formation of DP morphogenesis. Although appropriate Dpp signaling activity is required for proper PE formation, the detailed regulation mechanism is poorly understood. Here, we investigated the role of Dpp and its downstream target genes during the process of PE morphogenesis by genetic manipulation. Based on experiments, we found that:(1) As a signal transducer of Dpp, pMad was offen used as marker of Dpp signal activity. pMad was present in PE while Dpp target genes sal and omb were only expressed in DP but not PE cells.(2) The absence of Sal in PE was essential for PE formation. Ectopic expression of sal in the PE cells was sufficient to heighten the PE cells. Down-regulation of sal in the DP shortened the DP cell height.(3) We further demonstrated a known transcriptional factor Lines, which can convert PE into DP cell fate when it was misexpressed in PE. This function was mediated by sal, because co-expression sal-RNAi and lines largely restored PE cell morphology.(4) By revealing the microtubule distribution, we showed that Lines and Sal-heightened PE cells were morphologically closed to the intermediate cell with cuboidal morphology.This study deeply explored the important role of Dpp signaling during the process of squamous epithelium morphogenesis in Drosophila wing disc, we found gene sal act as a key factor in this process. As Sall family are highly conserved in organism, our study also provide new ideas for treating relevant human diseases.