Constitutive expression of interleukin-1 alpha messenger ribonucleic acid in rat sertoli cells is dependent upon interaction with germ cells

Interleukin-1 (IL-1), a proinflammatory cytokine originally isolated as a p roduct of activated mononuclear phagocytes, consists of two distinct agonis t proteins, IL-1 alpha and IL-1 beta, of which IL-1 beta is the major induc ible IL-1 protein produced by macrophages. We show here that mRNA of IL-1 a lpha, but not IL-1 beta, is constitutively expressed by the intact rat test is and localize the transcript to Sertoli cells as confirmed by a novel squ ash technique. The expression is developmentally regulated and appears only after postnatal day 20 in the rat testis, corresponding to onset of pubert y. IL-1 alpha mRNA shows a stage-de pendent expression pattern during the c ycle of the seminiferous epithelium. It is low or absent in stage VII, but present in all other stages of the cycle. The same stage-dependent distribu tion was also observed at the protein level when bioactive IL-1 was measure d in extracts of accurately defined one millimeter segments of seminiferous tubules. No IL-1 alpha mRNA was detected in adult rat testes after germ ce ll depletion by fetal irradiation or cytostatic drug treatment. Because sta ge VII is the only segment of the seminiferous tubules lacking DNA replicat ion, we propose that IL-1 alpha is involved in this event during mitosis an d meiosis of spermatogenesis and that its expression is dependent upon inte ractions between Sertoli cells and germ cells.