Sun1, an inner nuclear membrane protein, locates to telomeres and participates in postmitotic chromatin decondensation, but its functions in vivo have been subject to debate. Here, Kuan-Teh Jeang and co-workers report that Sun1 is required for the expression of coding and non-coding RNAs that are crucial for male gametogenesis(p. 965). Sun1–/– mice, they find, are born and grow normally, but are reproductively sterile; the males' gonads are significantly smaller than those of their wild-type counterparts, and spermatogenesis is disrupted. Sun1–/– testes also show reduced expression of genes that are associated with reproduction, including that of Mili and Miwi, two members of the Piwi gene family. Mili and Miwi participate in the biogenesis of Piwi-associated RNAs (piRNAs), which are crucial for germline development. The authors show that piRNA expression is also strongly reduced in Sun1 mutant animals, and propose that compromised RNA expression, as well as a previously recognised loss of telomeric attachments, in these mice contributes to their sterility.