Differences in regulation of testis specifc lactate dehydrogenase in rat and mouse occur at multiple levels.

The testis specific form of lactate dehydrogenase (LDH-C4) is encoded by a single locus, Ldh-c, and is tightly regulated in a tissue specific manner. Here we show differences in expression of Ldh-c between rat and mouse, and describe the levels at which regulation of this gene differs in the two species. Our results demonstrate that the Ldh-c message level is nearly nine fold greater in mouse testis and remains high post-meiotically. In contrast, rat Ldh-c mRNA is highest in primary spermatocytes and reduced in spermatids. The results of nuclear run-on assays indicate that the transcription rate of Ldh-c is only moderately higher in mouse than rat, and cannot account for a significant portion of the observed differences. Similar decay rates for both rat and mouse Ldh-c mRNA in actinomycin-D clearance assays indicate comparable cytoplasmic stabilities for the two messages. From these results we infer that nuclear prostranscriptional events contribute to the differences in Ldh-c message levels.