Isolation of a novel cDNA corresponding to a transcript expressed in the choroid plexus and leptomeninges

The CNS is composed of neurons and glial cells (i.e., astrocytes, oligodendrocytes, and microglia). The brain communicates with the blood circulation through choroid plexus and meninges as well as through the blood-brain barrier. To identify transcripts specifically expressed in a distinct brain cell type, we have previously constructed a subtracted cDNA library from the poly(A)+ RNAs of a velate protoplasmic-like astrocytic cell line, designated D19. This library was screened in order to isolate transcripts over-expressed in this astroglial cell line versus another astroglial cell line. Of the six recombinants which have been isolated, three sequences have not been described. Their sizes ranged from 100 to 200 bp and they hybridized to mRNAs expressed in vivo inside and outside the CNS. We have constructed a size-selected D19 cDNA library in order to obtain the full length cDNAs corresponding to the three undescribed sequences. We report here the isolation of a 1.6 kb cDNA corresponding to one of these recombinants, named p14. Its sequence has not yet been described and its deduced amino acid sequence codes for a 43 kDa protein with a putative signal peptide. In situ hybridization shows that this transcript is expressed at a high level in choroid plexus and leptomeninges and also in perivascular cells in the adult mouse brain. It is also expressed in cell subsets of kidney and gonads as well as in perivascular cells in skeletal and cardiac muscles. These localizations suggest that the encoded protein might be involved in transport processes and hormonally controlled.