Cloning, Characterization, and Developmental Expression of a Rat Lung Alveolar Type I Cell Gene in Embryonic Endodermal and Neural Derivatives

Abstract

We report here the identification and characterization of a novel gene, T1 alpha, expressed in high abundance in adult rat lung, fetal lung, and early fetal brain. T1 alpha was identified by a monoclonal antibody previously shown to be specific for an antigen expressed by alveolar epithelial type I cells. The cDNA for T1 alpha is 1.85 kb and identifies a single mRNA species of the same size on Northern blots of adult rat lung. The longest open reading frame of the cDNA is 498 bases which would encode a protein of approximately 18 kDa. The protein has a putative membrane spanning domain near the C-terminus but lacks consensus sequences for N-glycosylation. Northern blots and RT-PCR show high expression of T1 alpha in adult lung, with marginally detectable expression in adult brain, intestine, and kidney. RT-PCR analysis shows expression of T1 alpha in freshly isolated type I cells (50-60% purity) but not in highly purified type II cells or other lung cells. We believe therefore that T1 alpha is primarily if not uniquely expressed in alveolar type I cells in the adult rat. Polyclonal antisera against a 16-amino-acid peptide identified in the deduced sequence reacts with the apical membranes of adult type I cells in lung tissue sections but does not label other cell types. The above antiserum as well as the original monoclonal antibody recognize a single approximately 18-kDa protein derived from bacterial expression of a construct containing the T1 alpha open reading frame. By RT-PCR T1 alpha is detected in rat lung from Day 13.5 onward, but is detected by in situ hybridization earlier in lung, brain and neural derivatives, and foregut. Expression is down-regulated in all but lung tissues as development proceeds.

Ectopic Expression of PA2.26 Antigen in Epidermal Keratinocytes Leads to Destabilization of Adherens Junctions and Malignant Progression

“…OTS-8 was isolated as a phorbol ester-inducible gene from cultured osteoblasts (Nose et al, 1990), and gp38 was described as a marker of stromal cells in T-cell-dependent areas of peripheral lymphoid tissues (Farr et al, 1992). The rat (T1␣/E11/podoplanin), canine (gp40), and human (gp36) homologs to murine PA2.26 have also been reported by different laboratories (Breiteneder-Geleff et al, 1997;Rishi et al, 1995;Wetterwald et al, 1996;Zimmer et al, 1997Zimmer et al, , 1999. All these proteins have similar biochemical characteristics and tissular distributions.…”

“…All these proteins have similar biochemical characteristics and tissular distributions. Thus, for example, rat T1␣ sialoglycoprotein was first described as a marker of alveolar type I epithelial cells of the lung (Rishi et al, 1995), and human gp36 has been recently characterized as a mucin-type transmembrane sialoglycoprotein expressed at the apical plasma membrane of the vascular endothelium and alveolar epithelium (Zimmer et al, 1999). Although canine gp40 can act as a main receptor for the influenza C virus (Zimmer et al, 1995), and rat podoplanin was found to be down-regulated in an experimental model of minimal-change nephropathy (Breiteneder-Geleff et al, 1997), the biological functions of these proteins are unknown.…”

The potential role of podoplanin in tumour invasion

“…In normal human tissue, podoplanin is expressed in kidney podocytes (Breiteneder-Geleff et al, 1999), in skeletal muscle, placenta, lung and heart (Martin-Villar et al, 2005), in myofibroblasts of the breast and salivary glands, in osteoblasts and mesothelial cells (Ordonez, 2006b). It is also expressed on the apical surface of rat alveolar type I cells (Rishi et al, 1995). Occasionally, focal expression of podoplanin can be found in circumscribed areas of the basal layer of the human epidermis (Schacht et al, 2005).…”

Alterations in alveolar epithelium differentiation and vasculogenesis in lungs of LIF/IGF‐I double deficient embryos

“…At the saccular stage, type I cells increase in proportion lining the alveolar walls, providing a short diffusion pathway for gas exchange (Warburton et al, 2000;Compernolle et al, 2002;Chinoy, 2003). They express specific markers like aquaporin 5 (Aqp-5) and glycoprotein T1␣ (Rishi et al, 1995;Funaki et al, 1998;Williams, 2003).…”