NF‐κB is developmentally regulated during spermatogenesis in mice

To analyze NF‐κB activity in the testis, we used murine transgenic lines carrying a LacZ reporter gene under the control of a NF‐κB‐responsive promoter (Schmidt‐Ullrich et al. [1996] Dev 122:2117–2128). We constructed three independent lines containing the promoter of the gene encoding p105, the precursor of the p50 subunit. This promoter contains three NF‐κB‐binding sites in its proximal part. Our results show that in adult mice, the β‐galactosidase activity which reflects nuclear NF‐κB activity, is first detected in spermatocytes at the pachytene stage and remains activated in the following steps of germ cell differentiation and maturation. Using transgenic mice carrying a p105nlslacZ construct with the 3 NF‐κB sites mutated in the p105 promoter, we found a significant reduction in the transgene activity, confirming the important role of NF‐κB in the activation of the transgene. To confirm the stage of induction during spermatogenesis, we analysed the β‐galactosidase activity in the testes from prepuberal mice in which cells synchrouneously enter meiosis. We detected the transgene activity at 18 days after birth, corresponding to the pachytene stage in spermatocytes. In nuclear extracts prepared from prepuberal mice, we found a peak of NF‐κB DNA‐binding activity made of p50 and p65 subunits at day 18 after birth, which remains high in the later stages. Further analysis showed that IκBα and β, but not ϵ are expressed in the testes. Altogether, these data suggest that NF‐κB factors are stage specifically controlled and may play a role during the development of sperm cells. © 2000 Wiley‐Liss, Inc.