Expression of rat target of the antiproliferative antibody (TAPA) in the developing brain

The present study defines the expression pattern of TAPA (target of the antiproliferative antibody, also known as CD81) in the developing rat brain. TAPA is a member of the tetramembrane spanning family of proteins, and like other members of this family it appears to be associated with the stabilization of cellular contacts (Geisert et al. [1996] J. Neurosci. 16:5478-5487). On immunoblots of the brain, TAPA is present in higher levels than any other tissue examined: muscle, tendon, peripheral nerve, cartilage, liver, kidney, skin, and testicle. Immunohistochemical methods were used to define the distribution of TAPA in the brain. This protein is expressed by ependyma, choroid plexus, astrocytes, and oligodendrocytes. TAPA is dramatically upregulated during early postnatal development, at the time of glial birth and maturation. At embryonic day 18, the levels of TAPA are low, with most of the immunoreaction product being associated with the ependyma, choroid plexus, and the glia limitans. As development continues, the amount of TAPA expressed in the brain increases, and at postnatal day 14 the levels approach those of the adult. This increase in the levels of TAPA at postnatal day 14 is due to upregulation in the gray matter and white matter. Thus, TAPA is found in all glial cells, and the level of this protein correlates with their maturation.