English
The acquisition and loss of epithelial characteristics—such as apico-basal polarity, cell–cell adhesion, and barrier integrity—are essential processes during development, regeneration, and disease. While epithelial–mesenchymal transition (EMT) has been extensively studied, far less is known about the reverse process, mesenchymal–epithelial transition (MET), particularly in the context of organogenesis. Here, we investigate MET during \textit{Drosophila} embryonic midgut development, a system where endodermal cells transition into a structured, polarized epithelium in response to signals from the underlying visceral mesoderm. Despite knowledge of key mediators such as Laminins and Integrins, the broader transcriptional and regulatory programs orchestrating cell polarization, elongation, junction formation, and regional patterning remain incompletely understood.
To address this gap, we generated a high-resolution single-cell transcriptomic atlas of \textit{Drosophila} midgut development using SMART-seq-based full-length RNA profiling. This dataset comprises over 3,500 cells from wild-type and mutant (\textit{LanB2}, \textit{tinman}) embryos, with a median detection of over 4,300 genes per cell. Through trajectory inference, co-expression analysis, and SCENIC-based gene regulatory network modeling, we identified dynamic gene modules and transcription factor regulons that govern MET and spatial compartmentalization along the anterior–posterior axis. Our results show that MET is a progressive, region-specific process tightly coupled to differentiation, involving coordinated shifts in polarity markers, cytoskeletal genes, and signaling pathways.
Comparative analysis with \textit{LanB2} and \textit{tinman} mutants revealed that external cues from the mesoderm act in a permissive—rather than strictly instructive—manner to promote timely MET, with the MMG showing the greatest dependence on these interactions. Notably, some regions like the PMG retained epithelial differentiation programs even in the absence of mesodermal contact, albeit with delayed morphogenesis. We also uncovered novel candidate regulators such as \textit{GATAe}, \textit{fkh}, and \textit{Src64B}, as well as previously uncharacterized cell populations.
Altogether, this work provides the first single-cell resolution atlas of embryonic MET and midgut regionalization in \textit{Drosophila}. It establishes a valuable resource for studying epithelial morphogenesis and highlights the importance of integrating single-cell transcriptomics with spatial and genetic perturbation data to uncover the intrinsic and extrinsic principles driving epithelial tissue formation.
Keywords: Drosophila melanogaster, mesenchymal–epithelial transition, single-cell RNA-seq, midgut, embryogenesis
Persistent Address:
http://dx.doi.org/10.53846/goediss-11514
