Prenatal and postnatal histogenesis of myoepithelium in hamster submandibular gland. An ultrastructural study.

Prenatal and postnatal development of myoepithelium in the hamster submandibular gland has been studied by electronmicroscopy. Myoepithelial cells originate from 'undifferentiated' stem cells in the epithelial anlage at 14-1/2 days of gestation. At this stage of their cytodifferentiation, the myoepithelial cells are recognizable by their elongated shape, peripheral location between the basal lamina and other epithelial cells in the anlage, axially oriented dense nucleus and low density cytoplasm. The myofilament deposition starts at birth, initially in the basal cytoplasm. With advancing maturation, there is a progressive increase in the number of myofilaments and in two week-old animals they virtually fill the cytoplasm. The mature myoepithelial cells are characterized by their shape, location, cytoplasmic myofilaments which run parallel to the basal lamina and display focal densities along their course, hemidesmosomes and pinocytotic vesicles. The morphologic evidence supports their epithelial origin but militates against their ability to mediate the synthesis of fibrous, mucinous, chondroid or osseous material as proposed by others (Grishman, 1952; Azzopardi and Smith, 1959; Doyle et al., 1968; Hubner et al., 1971).