Comparative biology and expression of TENP, an egg protein related to the bacterial permeability-increasing family of proteins

• TENP expression is restricted to the oviduct, almost exclusively the magnum.
• Adult expression is almost 10,000x greater than in embryonic tissues.
• Expression is under the control of gonadal steroids.
• TENP is conserved across divergent avian species.

The ‘transiently expressed in neural precursors’ (TENP) gene product is a member of the bacterial/permeability-increasing (BPI) family of antimicrobial proteins but was first identified as having a role in an early neurological event occurring in post-mitotic cells. However, recent characterisation of the egg white proteome has shown that TENP is an important egg component constituting ~ 0.1–0.5% of the total protein and suggesting it is expressed in the adult oviduct. In this study we confirmed quantitatively that the expression of TENP is largely confined to the tubular glands of the magnum of the oviduct, where egg white synthesis occurs, with around 10,000 times more expression than in the embryo where TENP was first identified. TENP expression is significantly increased with the administration of oestrogen or progesterone (P < 0.001) and is reduced in regressed oviducts (P < 0.001) demonstrating gonadal steroid control, typical of an oviduct and egg specific gene. A putative translational start site for TENP has been characterised and the evidence indicates that it is expressed as one predominant transcript. In comparison with the published sequence, insertion and deletion events have been identified causing a partial frame-shift that results in an altered amino acid sequence to that previously documented. TENP is conserved across divergent avian species being found in chicken, turkey, duck and zebra finch and its expression profile confirmed in both chicken and duck. Similarity searches have shown homology with the BPI-like family of innate immune genes, particularly with palate, lung and nasal epithelial clone (PLUNC) members of this family. We therefore believe that at least in adults the role of TENP is as a major component of egg, particularly the white and it is probable that it contributes to its antimicrobial function.