The testis chromatin undergoes profound structural alterations and functional changes during spermatogenesis. Changes in DNA methylation have been correlated with gene expression in a number of systems, but the relationship between methylation and gene expression for testicular genes is unclear. To address this question, DNA methylation patterns and mRNA expression for a somatic form of lactate dehydrogenase (LDH), LDH-A, were compared with those of the testis-specific form, LDH-C, in preparations from testes of prepubertal and sexually mature mice, from isolated testicular cells, and from somatic tissues. At specific sites, LDH-A was less methylated in adult testis than in spleen DNA; the decreased methylation in the testicular DNA occurred as early as type A spermatogonia. In contrast, DNA methylation patterns for LDH-C did not differ between spleen and testis DNAs. In Northern blots, the levels of LDH-A transcripts were low in total testis RNA obtained from 6-12-day-old mice, and in type A and B spermatogonia from 8-day-old mice. LDH-A mRNA levels increased gradually in testes from 16-45-day-old mice. LDH-C transcripts were first detectable in the testes of 12-day-old mice and increased as spermatogenesis proceeded. Both LDH-A and LDH-C mRNA levels were low in preleptotene spermatocytes and leptotene/zygotene spermatocytes and increased substantially in pachytene spermatocytes and round spermatids. Reduced levels of LDH-A and LDH-C mRNAs were found in the residual bodies/cytoplasts fraction.(ABSTRACT TRUNCATED AT 250 WORDS)