Development of the smooth muscle layer in the ileum of mouse embryos
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ORIGINAL ARTICLE
Development of the smooth muscle layer in the ileum of mouse embryos Esrat Jahan1 · Ashiq Mahmood Rafiq2 · Akihiro Matsumoto1 · Nusrat Jahan1 · Hiroki Otani1 Received: 24 April 2020 / Accepted: 17 August 2020 © Japanese Association of Anatomists 2020
Abstract The smooth muscle layer (SML) comprises a significant portion of the intestines and other tubular organs. Whereas epithelial development has recently been extensively studied, SML development has drawn relatively less attention. Previous morphological reports revealed that the inner circular layer (IC) differentiates earlier than the outer longitudinal layer (OL), but detailed development of the SML, including chronological changes in the cell layer number, precise cell orientation, and regional differences in relation to the mesentery, has not been reported. We here observed the development of the SML in the C57BL/6J mouse ileum near the ileocecal junction at embryonic day (E) 13.5, 15.5, and 17.5. By histo-morphometric analyses, in IC, smooth muscle cells (SMCs) were oval-shaped and irregularly arranged in 3–4 layers at E13.5, then adopted an elongated spindle shape and decreased to two cell layers at E15.5 and E17.5. The IC SMC nuclear angle was not vertical, but oriented at 60–80° against the mid-axis of the intestinal lumen. The single SMC layer in OL was observed at E17.5, and the SMC nuclear angle was parallel to the luminal mid-axis. No clear regional difference against the mesentery was observed. Collectively, the findings suggest that development and differentiation of the ileal SML is not simple but regulated in a complex manner and possibly related to the macroscopic organogenesis. Keywords Smooth muscle cell · Inner circular layer · Ileum · Mouse · Embryo
Introduction The intestinal wall consists of the luminal epithelium, connective tissue, smooth muscle layer (SML), and covering serosa. Through the organogenetic and histogenetic periods, the luminal epithelium and glands develop from the endoderm, whereas the covering mesoderm develops into the connective tissue, blood vessels, smooth muscle cells (SMCs) of the lamina muscularis mucosae, and SML, together with the myenteric ganglia (for review, see Young 2008). Since the intestine not only develops radial layers Esrat Jahan and Ashiq Mahmood Rafiq equal first authors. * Hiroki Otani [email protected]‑u.ac.jp 1
Department of Developmental Biology, Faculty of Medicine, Shimane University, 89‑1 Enya‑cho, Izumo, Shimane 693‑8501, Japan
Center for the Promotion of Project Research, Organization for Research and Academic Information, Shimane University, 1060 Nishikawatsu‑cho, Matsue, Shimane 690‑8504, Japan
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but also elongates and increases its luminal surface area in a manner disproportionate to the increase in body size over these periods, there must be mechanisms to ensure that these events occur in each tissue part. Further, the disproportionately elongated intestine must be folded and arranged in a basically reproducible fashion in the limited space of the abdomi
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