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

The testis specific form of lactate dehydrogenase (LDH‐C 4 ) 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. © 1993 Wiley‐Liss, Inc.