TISSUE INTERACTION REGULATES EXPRESSION OF A SPASMOLYTIC POLYPEPTIDE GENE IN CHICKEN STOMACH EPITHELIUM

The primitive epithelium of embryonic chicken proventriculus (glandula r stomach) differentiates, after day 6 of incubation, into luminal epi thelium, which faces the lumen and abundantly secretes mucus, and glan dular epithelium, which invaginates into mesenchyme and later expresse s embryonic chicken pepsinogen (ECPg). So far it is not well understoo d how undifferentiated epithelial cells differentiate into these two d istinct cell populations. Spasmolytic polypeptide (SP) is known to be expressed in surface mucous cells of mammalian stomach. In order to ob tain the differentiation marker for proventricular luminal epithelial cells, we cloned a cDNA encoding chicken SP (cSP). Sequence analysis i ndicated that cSP has the duplicated cysteine-rich domain characterist ic of SP. Examination of the spatial and temporal expression pattern o f cSP gene revealed that, during embryogenesis, cSP was expressed in l uminal epithelial cells of the proventriculus, gizzard, small intestin e, and lung, but not the esophagus. In the proventriculus, cSP mRNA wa s first detected on day 8 of incubation and was localized to different iated luminal epithelial cells. By using cSP as a molecular marker, th e effects of mesenchyme on the differentiation of epithelium were anal yzed in vitro. On the basis of these data, a model is presented concer ning the differentiation of proventricular epithelium.