Developmental and differential expression of the ornithine decarboxylase gene in rodent testis

Ornithine decarboxylase (ODCase) is the first and rate-limiting enzyme in the polyamine biosynthetic pathway and it is androgen regulated in the mouse. The expression of ODCase transcripts during testicular development was examined by Northern blot analysis with a mouse ODCase cDNA probe. Total RNA was isolated from the testes of prepubertal mice at 6, 8, 12, 16, 18, 20, 22, and 30 days of age, from enriched populations of germinal cells obtained from the testis of immature (8 days old) and mature (45 days old) mice and from several mouse somatic tissues. The level of the two ODCase transcripts (2.2 and 2.7 kilobases) was low but detectable in the testes of 6- to 16-day-old mice and increased substantially as the first spermatogenic wave proceeded into spermiogenesis. The low ODCase mRNA levels observed in prepubertal mouse testes were confirmed with RNA samples obtained from enriched germ cell populations of type A and type B spermatogonia and interstitial cells obtained from Day 8 mouse testes. In agreement with the developmental studies, ODCase mRNA levels increased substantially in enriched populations of pachytene spermatocytes, round spermatids, and residual bodies/cytoplasts isolated from mature testes. Similar results were obtained by in situ hybridization of sections of rat testes. Reduced levels of ODCase transcripts were detected in RNA obtained from cultured mouse Sertoli cells obtained from the testes of 21-day-old mice and in RNA from liver, brain, heart, spleen, seminal vesicle, and aorta. In contrast, ODCase transcript levels from kidneys of male mice were as high as those detected in testis RNA. Substantial levels of ODCase mRNAs were also found in the epididymis. Analysis of polysome gradients prepared from total testis extracts revealed a distribution of ODCase mRNA in both nonpolysomal and polysomal fractions of the gradient, suggesting that ODCase is translationally regulated in the mouse testis.