RETINOID STATUS CONTROLS THE APPEARANCE OF RESERVE CELLS AND KERATIN EXPRESSION IN MOUSE CERVICAL EPITHELIUM

We describe an animal model to induce the histogenesis of squamous met aplasia of the cervical columnar epithelium, a condition usually prece ding cervical neoplasia. This model is based on dietary retinoid deple tion in female mice. Control sibling mice fed the same diet but with a ll-trans-retinoic acid (at 3 mug/g diet) showed the normal endocervica l epithelial and glandular columnar morphology, typical of a simple ep ithelium without subcolumnar reserve cells. The stratified squamous ec tocervical epithelium of these mice fed all-trans retinoic acid showed intense immunohistochemical staining in basal and suprabasal cells wi th monospecific antibodies against keratins K5, K14, K6, K13, and, sup rabasally, with antibodies specific for Kl and K10. At the squamocolum nar junction, the adjacent columnar epithelium (termed ''suprajunction al'') did not show staining for K5, K14, K6, K13, K1, and K10 but spec ifically stained for keratin K8, typical of simple epithelia and absen t from the adjacent ectocervical squamous stratified lining (termed '' subjunctional''), in striking contrast. Sections of the squamocolumnar junction from mice kept on the vitamin A-deficient diet for 10 weeks showed suprajunctional isolated patches of reserve cells, proximal and distal to the junction. These cells were detected prior to any sympto ms of vitamin A deficiency, such as loss of body weight or respiratory discomfort. The subcolumnar reserve cells induced by vitamin A defici ency displayed positive staining for K5 and K14. As deficiency became severe, the reserve cells occupied the entirety of the suprajunctional basement membrane. This epithelium eventually became stratified and s quamous metaplastic, the squamocolumnar junction was no longer discern ible, and the entire endocervical epithelium and the endometrial gland s lost K8 positivity, while acquiring K5, K14, K6. K13, K1. and K10 ke ratins typical of the ectocervix under normal conditions of vitamin A nutriture. Vitamin A deficiency also altered keratin expression and lo calization in squamous subjunctional epithelium. In situ hybridization studies for K1 and K5 mRNA showed their major site of expression at t he basal (K5) and immediately suprabasal (K1) cell layers. The localiz ation of both K5 and KI proteins in these same cell layers, and above, is consistent with transcriptional regulation of these keratins. Earl y vitamin A deficiency caused the appearance of single subcolumnar res erve cells expressing K5 mRNA. After these cells grew into a squamous focus. K1 mRNA became expressed suprabasally. We conclude that retinoi d status plays a key role in maintaining differentiative characteristi cs of the cervical and glandular epithelia and, as such, may be a modu lating factor in the development of cervical cancer.