Developmental expression of murine Beta-trace in embryos and adult animals suggests a function in maturation and maintenance of blood-tissue barriers.

The complete cDNA for murine Beta-trace protein was isolated by RT-PCR using degenerate primers designed according to amino acid sequences derived from tryptic peptides. It encodes a protein of 165 amino acids (calculated molecular weight 18,472 Da) with a predicted 24-amino-acid leader peptide. In situ analyses during mouse embryonic development and in adult animals revealed a specific temporal expression pattern of Beta-trace. Beta-Trace mRNA was initially detected at 14.5 days postconception in mesenchymal cells destined to become leptomeninges and in the developing testis. Later in development, a lower level of expression was additionally observed in choroid plexus epithelium, in strictly confined regions of the eye (pigment and ciliary epithelium), in the ear (cochlear duct), and within single cells in the brain. Expression was also found in epithelia of the epididymis and the testis Leydig cells of postpubertal animals. The highly specific expression at blood-tissue barriers such as the blood-cerebrospinal fluid, blood-retina blood-aqueous humor, and blood-testis barriers indicates a potential role for this lipocalin in transport and/or in maturation and maintenance of these barriers.