Vitamin A deficiency alters the expression of mucin genes by the rat ocular surface epithelium

Purpose. To study effects Of depletion of retinoic acid on expression of th e mucins ASGP (rMuc4), rMuc5AC, and rMuc1, by the corneal and conjunctival epithelia of the rat. Methods. Nineteen-day-old Sprague-Dawley male rats were fed a casein-based vitamin A- deficient diet or casein-based diet with vitamin A as control. R ats from both groups were killed at 1, 3, 5, 13, 15, 18, and 20 weeks after initiation of feeding. Expression of the three mucin genes by the ocular s urface epithelium was assayed by reverse transcription-polymerase chain rea ction (RT-FCR) and in situ hybridization. Results. In vitamin A-deficient rats, ASGP mRNA was not detected by RT-PCR after 15 weeks of feeding. rMuc5AC mRNA was detected by RT-PCR at 15 weeks, but by 18 and 20 weeks was no longer detectable. By in situ hybridization, ASGP mRNA was localized in the entire ocular surface epithelium after 1 we ek of feeding, was diminished bur detectable above background by 13 weeks, and was not detectable at 20 weeks. rMuc5AC mRNA was detected in the goblet cells of vitamin A-deficient rats by in situ hybridization at 13 weeks, bu t was lost by 20 weeks, as were identifiable goblet cells. nMuc1 mRNA were detected by RT-PCR through all time points of 1 to 20 weeks in both vitamin A-deficient and control rats, indicating no significant change in rMuc1 mR NA expression with vitamin A deficiency. Conclusions. Both the membrane-spanning mucin ASGP (rMuc4) and the secretor y mucin rMuc5AC are directly or indirectly regulated by vitamin A in the oc ular surface epithelium, whereas the membrane-spanning mucin rMuc1 is not.