Excess retinoid acts through the stroma to produce mucous glands from newborn hamster cheek pouch in vitro.

Many morphogenetic processes are modified or initiated by retinoids. The cheek pouch of the newborn hamster can be induced to develop mucous glands in vitro by adding excess retinoid. The objective of this study was to determine whether the retinoid acted through the epithelium or the mesenchymal stroma. Explants of cheek pouch were grown for 7 days in either standard medium, or medium supplemented with 6 micrograms/ml retinyl acetate (RAc; 1.8 x 10(-5) M). After separation of most explants into epithelium and mesenchyme by trypsinization, the separated tissues were recombined in all possible ways and cultured for a further 1-2 weeks in standard medium. All explants were analysed histologically and/or histochemically from complete serial paraffin sections. No glands were formed in 30 recombinants containing stroma that had not been exposed to RAc, but four of 25 recombinants containing previously exposed stroma had glands, as well as four of 18 unseparated explants exposed to RAc. Exposure of epithelium to RAc did not result in the incidence of glands. It was concluded that RAc acting through the stroma was responsible for the instructive interaction with the epithelium for gland formation. A molecular mechanism is suggested.

Stability of the glandular morphogenesis produced by retinoids in the newborn hamster cheek pouch in vitro.

Retinoids can induce alterations in differentiation and morphogenesis in the hamster cheek pouch. In order to determine the stability of these changes, explants of neonatal pouch were exposed to 6 micrograms/ml of either retinyl acetate (RAc: 1.8 x 10(-5) M) or all-trans retinoic acid (RA: 2.0 x 10(-5) M) for an initial 3 of 7 days, out of a total of 21 days in organ culture. Three days of RAc or RA caused a delay in the differentiation and keratinization of the epithelium at least up to day 7 of culture. Additionally, two out of ten explants exposed to RA showed small downgrowths of epithelium into the stroma at 7 or 14 days. Seven days of exposure to either retinoid led to inhibition of epithelial keratinization, and produced a mucous metaplasia which was still seen at the end of the 21-day culture period. Periodic acid-Schiff (PAS)-positive, diastase-resistant material was present in the metaplastic epithelium, in intercellular, and in some instances, intracellular locations. An excess of either RAc or RA, for 7 days, induced persistent glandlike downgrowths of epithelium, suggesting that a stable alteration in the developmental program of the epithelium may have occurred. Many of these downgrowths possessed a lumen which was lined by cuboidal epithelium and contained PAS-positive, diastase-resistant secretory material. RA appeared more potent than RAc in inhibiting keratinization, in producing a mucous metaplasia, and in initiating glandlike downgrowths. The persistence of glandular downgrowths suggests that retinoids, either directly or indirectly, act in a manner similar to that of an embryonic inductor.

The development of the Syrian hamster cheek pouch.

The objective of this study was to provide a detailed account of the morphogenesis and early cytodifferentiation of the hamster cheek pouch. Although the newborn "cheek pouch" is used for in vitro studies of the effects of retinoids and carcinogens, its rudimentary structure has not been adequately described. Complete paraffin serial sections of the heads of 14- and 15-day fetuses were cut in three planes to determine the location and shape of the earliest pouch rudiments. Complete paraffin serial sections were prepared from pouch rudiments dissected from hamsters at birth and at daily intervals from 3 to 12 days postnatal. Semithin Epon sections were examined by light microscopy and ultrathin sections by transmission electron microscopy. The pouch can appear in the fetus as two solid epithelial ingrowths from the lining of the oral cavity. They are the margins of an ingrowing sheet of oral epithelium which becomes leaflike at about the time of birth, as it grows caudad into the tissue of the cheek. The central cells of the ingrowth accumulate large quantities of glycogen before differentiating as a stratum spinosum 5 days after birth. Within the stratum spinosum, groups of cells containing keratohyalin granules initiate the stratum granulosum. Keratinized cells appear within the stratum granulosum areas. Spaces appear between keratinized cells, and the spaces coalesce to form the pouch cavity between 7 and 12 days postnatal. Soon afterward, this cavity opens to the oral cavity to make a pouch, and the ultrastructure of the cheek pouch epithelium closely resembles that of the adult.