Expression of ras proto-oncogene proteins in normal human tissues

The expression of ras proto-oncogenes in normal human tissues was studied by immunohistochemical staining and by immunoblotting using monoclonal antibodies. We detected p21(ras) protein in almost every fetal and adult tissue, but the level varied significantly among cell types. In some cell lineages, immature cells capable of proliferation contain more p21(ras) than do mature cells. By contrast, certain fully differentiated cells, such as neurons and the epithelial cells of endocrine glands, express abundant p21(ras). Among mammalian tissues the highest level of ras protein was detected in brain. Crude synaptosomal membrane preparations from rat brain contain substantially more p21(ras) than do plasma membranes from rat liver. The observed distribution of p21(ras) suggests a role for these proteins both in cellular proliferation and in certain specialized cellular functions.