TYPE-XVII COLLAGEN (BP-180) IN THE DEVELOPING AVIAN CORNEA

Purpose. Previous sequence analyses of hemidesmosomal BP 180/collagen XVII cDNA from human skin and of a similar chicken corneal cDNA showed some similarities, but major differences as well. The authors examine d whether, in one species, the same mRNA is present in cornea and skin . They also studied the developmental expression of the molecule and c ompared it to the transmembrane hemidesmosome component, alpha 6 beta 4 integrin, and to the formation of hemidesmosomes themselves. Methods . Cornea and skin BP 180/collagen XVII cDNAs were cloned by reverse tr anscription-polymerase chain reaction (RT-PCR) and sequenced. Developm ental expression was evaluated by quantitative RT-PCR, immunoblotting, and immunofluorescence microscopy. alpha 6 beta 4 integrin was evalua ted by immunofluorescence microscopy, and hemidesmosome formation was assessed by electron microscopy. Results. The same al (XVII) collagen/ BP 180 mRNA is present in cornea and skin. The appearance of alpha 1 ( XVII) collagen mRNA and protein shows similar temporal patterns of exp ression, with changes in the mRNA preceding those of the protein by ap proximately 2 days. The appearance of mature hemidesmosomes lags still further. Immunofluorescence histochemistry of al (XVII) collagen and alpha 6 beta 4 integrin shows that their developmental appearance is r egulated closely. Conclusions. The differences between human BP 180/co llagen XVII and the chicken corneal molecule represent species diverge nce. The appearance of alpha 1 (XVII) collagen mRNA and protein is reg ulated closely, with the protein lagging. Mature hemidesmosomes, once present, have a low turnover rate. The developmental appearance of alp ha 1 (XVII) collagen and alpha 6 beta 4 integrin are regulated closely . However, the component responsible for initiating hemidesmosome form ation remains unknown.