The morphology of the basal lamina and periepithelial collagen during growth and branching of the embryonic lung of mice (day 14 to 16).
In order to be able to interpret the developmental mechanism of the epithelial branching pattern, we investigated lung development of mouse embryos of gestational days 14 to 16 electron microscopically. Various fixation techniques (Karnovsky, tannic acid, ruthenium red) were employed. Four regions could be distinguished in a growing and branching epithelial bud: 1) the epithelial tube before the site of branching; 2) the actual site and gap of branching; 3) the already formed part of the new buds and 4) the actual leading, i.e., the growing tip. Regions 1 and 3 were characterized by a continuous basal lamina and a more (1) or less (3) thick sheath of accompanying collagen. The site of branching (2) showed a pronounced folding of the basal lamina to which numerous collagenous fibrils were attached. At the distal, i.e., growing site (4) the basal lamina was characterized by numerous interruptions; accompanying collagen was missing. Immunomorphological investigations of regions 1 to 3 revealed all components of a basal lamina and collagen types I, III and V and fibronectin at the border between epithelium and connective tissue. However, this amount was clearly reduced at the growing tip, and collagen type I was missing. These findings help to understand and elucidate the importance of the mesenchyme for the growth and branching process and the development of the branching pattern.
Csato
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Institut für Toxikologie und Embryonal-Pharmakologie, Freie Universität Berlin, FRG.
D000818:Animals; D001980:Bronchi / Q000196:embryology; D003094:Collagen / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D008168:Lung / Q000033:anatomy & histology / Q000196:embryology*; D051379:Mice; D008854:Microscopy, Electron; D011247:Pregnancy; D016707:Tissue Fixation
D003094:Collagen