MULTIPLE ISOFORMS OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA-5-]4-ISOMERASE IN MOUSE-TISSUES - MALE-SPECIFIC ISOFORMS ARE EXPRESSED IN THE GONADS AND LIVER/

Multiple isoforms of 3beta-hydroxysteroid dehydrogenase/DELTA5-->4-iso merase (3betaHSD) are expressed in various mouse tissues in a tissue-s pecific, sex-specific, and developmental manner. Three distinct immuno reactive species [molecular masses, 47, 44, and 42 kilodaltons (kDa)] are detectable by Western immunoblot analysis using a 3betaHSD antiser um. Different immunoreactive isoforms are expressed in steroidogenic ( 44 and 47 kDa in gonads) and nonsteroidogenic (42 and 47 kDa in liver and kidney) tissues. Two of these isoforms are sex-specific in the gon ads (47 kDa) and liver (42 kDa), because they are detectable only in m ale mice. Sex-specific expression in the liver is developmentally regu lated. Low levels of this male-specific hepatic isoform are first dete ctable at 23-25 days of age, but its level of expression increases pro gressively during sexual maturation to adult levels. NAD+-dependent 3b etaHSD activity is detectable in homogenates of all tissues examined, but the kinetic characteristics of this activity differ among tissues and are sexually dimorphic in the liver. Apparent Michaelis constants for dehydroepiandrosterone are much lower in steroidogenic (0.24 +/- 0 .07 muM for testis) than in nonsteroidogenic (range, 10-100 muM for li ver and kidney) tissues and are lower in male mouse liver (16 +/- 1 mu M) than in female mouse liver (82 +/- 20 muM). Oligonucleotides with u nique sequences but encoding homologous regions of the mouse type I, I I, and III 3betaHSD cDNAs were used for Northern blot analyses. A type I oligomer hybridizes with RNA from steroidogenic (adrenal, ovary, an d testis) tissues, and a type III oligomer hybridizes with RNA from no nsteroidogenic (liver and kidney) tissues. A type II oligomer, however , hybridizes specifically with RNA from testis and liver of male mice, tissues that express a male-specific 3betaHSD. These results suggest that type II-like transcripts may encode a 47-kDa sex-specific 3betaHS D in testis and a 42-kDa sex-specific 3betaHSD in liver of male mice. It is unclear how many members or subfamilies of the 3betaHSD gene fam ily will be discovered. The mouse may prove to be a valuable experimen tal model, as this is the first species in which multiple immunoreacti ve isoforms can be identified in a single tissue. This multiplicity ma kes it difficult to correlate the size and number of immunoreactive is oforms with the diverse kinetic characteristics of NAD+-dependent 3bet aHSD activities in tissue homogenates and to develop isoform-specific probes. However complex, it is fortuitous that immunoreactive isoforms of mouse 3betaHSD can be size-fractionated electrophoretically. This could be used advantageously, because the multiplicity of 3betaHSD iso forms in the mouse is probably representative of that in other species .