2 CLOSELY-RELATED RECEPTOR-TYPE TYROSINE PHOSPHATASES ARE DIFFERENTIALLY EXPRESSED DURING RAT LUNG DEVELOPMENT

Transmembrane protein tyrosine phosphatases (PTPases) comprise a newly identified class of receptor-like molecules, In most cases their liga nds and the substrates they dephosphorylate are not known. In order to begin to explore the functions of the PTPases in cell physiology and in mammalian development, we examined the expression patterns of two c losely related receptor-type tyrosine phosphatase genes, namely LAR an d PTP delta, in fetal rat lung and in selected adult rat tissues. In t he lung, in situ hybridization and immunohistochemistry show that the LAR mRNA and protein are expressed exclusively in the epithelium, In t he early embryonic or fetal lung (day 13 to 18) LAR is expressed by al l of the epithelial. cells of the forming bronchial tree. This widespr ead pattern of expression is lost later in fetal life (day 21) as the lung matures and acquires the morphologic and biochemical features of the adult organ, LAR gene expression is then confined to two epithelia l progenitor cells of the distal airways, namely the bronchiolar Clara cell and the alveolar type II cell. The LAR gene products were also f ound abundantly expressed in epithelial progenitor cells of adult esop hagus, skin, and small intestine, all of which are continuously renewi ng epithelia. The rat PTP delta gene, on the other hand, is specifical ly expressed in the mesenchyme of the developing lung, The level of th e PTP delta mRNA decreases as the lung matures, These results suggest that the two closely related receptor-type tyrosine phosphatases are d ifferentially expressed in a tissue-specific fashion. They are express ed mostly in proliferating cells or in cells which have potential to p roliferate. Therefore, one function of the two receptor-like tyrosine phosphatases may be to regulate proliferation and/or differentiation o f different types of cells during development, during normal cell turn over, and during adult tissue repair. (C) 1995 Wiley-Liss, Inc.