Makanya A N, Hlushchuk R, Duncker H-R, Draeger A, Djonov V
Department of Veterinary Anatomy, University of Nairobi, Nairobi, Kenya.
Dev Dyn. 2006 Jan;235(1):68-81. doi: 10.1002/dvdy.20627.
The tall epithelium of the developing chick embryo lung is converted to a squamous one, which participates in formation of the thin blood-gas barrier. We show that this conversion occurred through processes resembling exocrine secretion. Initially, cells formed intraluminal protrusions (aposomes), and then transcellular double membranes were established. Gaps between the membranes opened, thus, severing the aposome from the cell. Alternatively, aposomes were squeezed out by adjacent cells or were spontaneously constricted and extruded. As a third mechanism, formation and fusion of severed vesicles or vacuoles below the aposome and their fusion with the apicolateral plasma membrane resulted in severing of the aposome. The atria started to form by progressive epithelial attenuation and subsequent invasion of the surrounding mesenchyme at regions delineated by subepithelial alpha-smooth muscle actin-positive cells. Further epithelial attenuation was achieved by vacuolation; rupture of such vacuoles with resultant numerous microfolds and microvilli, which were abscised to accomplish a smooth squamous epithelium just before hatching.
发育中的鸡胚肺的高柱状上皮会转变为鳞状上皮，后者参与薄气血屏障的形成。我们发现这种转变是通过类似外分泌的过程发生的。最初，细胞形成腔内突起（aposomes），然后建立跨细胞双膜。膜之间的间隙打开，从而将aposome与细胞切断。或者，aposomes被相邻细胞挤出，或者自发收缩并挤出。作为第三种机制，aposome下方切断的囊泡或液泡的形成和融合以及它们与顶侧质膜的融合导致aposome的切断。心房开始通过上皮逐渐变薄以及随后在由上皮下α平滑肌肌动蛋白阳性细胞划定的区域中周围间充质的侵入而形成。通过空泡化实现进一步的上皮变薄；这些空泡破裂，产生许多微褶和微绒毛，在孵化前这些微褶和微绒毛被切除以形成光滑的鳞状上皮。
