AJP - Lung Cellular and Molecular Physiology, Vol 267, Issue 5 531-L542, Copyright © 1994 by American Physiological Society
Spatial and temporal distribution of insulin-like growth factors I and II during development of rat lung
L. D. Wallen and V. K. Han
Department of Pediatrics, University of Western Ontario, Lawson Research Institute, London, Canada.
Insulin-like growth factors (IGF) I and II genes are expressed in
developing lung tissue, but the details of distribution during different
stages of lung development have not been delineated. To define the role of
IGFs in lung development, the expression of IGF-I and IGF-II mRNAs and
peptides was examined in rat lungs from 16-day gestation through adulthood.
The expression of stable IGF mRNAs was investigated by Northern analysis,
IGF mRNAs were localized by in situ hybridization histochemistry, and IGF
peptides were localized by immunohistochemistry. Four IGF-II transcripts
(3.5, 2.2, 1.8, and 1.0 kb) were identified; IGF-II mRNA levels were
highest early in fetal life (day 16-18) and decreased gradually until 28
days postnatal. Four IGF-I transcripts (7.8, 4.4, 2.1, and 0.6 kb) were
detected but were of low abundance. IGF-II mRNA was localized mainly in
mesenchymal cells but was also identified in the airway epithelium, with
peak expression in the perinatal lung. IGF-II peptide was prominent in late
fetal life and for 5 days after birth and was identified in both
mesenchymal and epithelial cells. In contrast, there was little evidence of
IGF-I mRNA and peptide until after birth: IGF-I was most easily identified
between 5 and 14 days postnatal (the height of alveolar multiplication and
formation), when both mRNA and peptide were localized to mesenchymal and
epithelial cells. Our studies demonstrate that IGF-I and IGF-II are
synthesized and distributed in spatially and temporally different patterns
in the developing lung. IGF-I and IGF-II peptides are more widely
identified than their respective mRNAs, suggesting a paracrine distribution
in the developing lung.
