ORIGIN AND MIGRATORY PATHWAYS OF THE 11 EPITHELIAL-CELL TYPES PRESENTIN THE BODY OF THE MOUSE STOMACH

The secretions of the mammalian stomach are produced by cells present in invaginations of the epithelium, which in the mouse are straight tu bules referred to as ''zymogenic units.'' These units comprise four re gions, namely pit, isthmus, neck, and base, in which there are several cell lineages with different phenotypes and migratory pathways. In th e isthmus, stem cells designated ''undifferentiated granule-free cells '' undergo division so as to maintain their own number and produce sev eral differently oriented progenitors: (1) ''Pre-pit cell precursors'' are characterized by prosecretory Golgi vesicles with a uniform, fine particulate content. They give rise to ''pre-pit cells'' defined by t he presence of few dense mucous granules. These cells migrate outward from the isthmus to the pit, where they become the dense granule-rich ''pit cells'' which populate the pit region and migrate to the gastric surface where they are lost. (2) ''Pre-neck cell precursors'' are ide ntified by prosecretory Golgi vesicles containing an irregular dense c enter and a light rim. They give rise to ''pre-neck cells'' defined by a few mucous secretory granules with a clear-cut core. These cells mi grate inward from the isthmus to the neck where they become ''neck cel ls,'' which contain many such granules. Even though neck cells are mat ure mucus-producers, they are not end cells. As they enter the base re gion, they become ''prezymogenic cells'' whose phenotype gradually cha nges from mucous to serous. These cells eventually lose the ability to produce mucus and thus become the typical zymogenic cells that popula te the base region. (3) ''Pre-parietal cells'' are classified into thr ee variants, which probably come from three different sources, that is , pre-pit cell precursors, pre-neck precursors, and the undifferentiat ed granule-free cells themselves. The pre-parietal cells mature into p arietal cells which migrate either outward to the pit or inward to the neck and base. As a result, parietal cells are scattered in the four regions of the unit. (4) Precursors Of ''entero-endocrine'' and ''cave olated'' cells give rise in the isthmus to these cells, which may also migrate outward or inward. (C) 1995 Wiley-Liss, Inc.