TGF-ß in tolerance, development and regulation of immunity.

The TGF-ß superfamily is an ancient metazoan protein class which cuts across cell and tissue differentiation, developmental biology and immunology. Its many members are regulated at multiple levels from intricate control of gene transcription, post-translational processing and activation, and signaling through overlapping receptor structures and downstream intracellular messengers. We have been interested in TGF-ß homologues firstly as key players in the induction of immunological tolerance, the topic so closely associated with Ray Owen. Secondly, our interests in how parasites may manipulate the immune system of their host has also brought us to study the TGF-ß pathway in infections with longlived, essentially tolerogenic, helminth parasites. Finally, within the spectrum of mammalian TGF-ß proteins is an exquisitely tightly-regulated gene, anti-Müllerian hormone (AMH), whose role in sex determination underpins the phenotype of freemartin calves that formed the focus of Ray's seminal work on immunological tolerance.

Candidate Sertoli cell specific promoter element for a TGFbeta family member (Amh) and a 3' UTR enhancer/repressor for the same gene.

Comparison between 400 nt of mouse DNA sequence immediately upstream (5') of the coding sequence of the Sertoli cell expressed genes, Amh and Tsx, identified a 33 nt sequence with a significant identity: this was considered to be a candidate Sertoli specific regulatory element (SSRE). Another highly conserved sequence has been identified immediately downstream (3') of the Amh polyadenylation signal (DSRE). The action and specificity of these two putative regulatory elements, inserted into a reporter vector (pd2EGFP), has been investigated by transient transfection of mouse fibroblast and Sertoli cells. When combined together or alone, with a minimal thymidine kinase (Tk) promoter, SSRE showed a weak incremental action on the expression of the reporter gene, regardless of the cell type: in contrast there was a 2- to 3-fold decrease when DSRE was present. However, in the absence of Tk there was evidence for a strong synergy between SSRE and DSRE, which was significantly greater in the Sertoli as compared with the fibroblast cells. These results support the view that SSRE exhibits a degree of Sertoli specificity and acts synergistically with DSRE in controlling the expression of Amh.