MULTIPLE ISOFORMS OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA-5-]4-ISOMERASE IN MOUSE-TISSUES - MALE-SPECIFIC ISOFORMS ARE EXPRESSED IN THE GONADS AND LIVER/
Ds. Keeney et al., MULTIPLE ISOFORMS OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA-5-]4-ISOMERASE IN MOUSE-TISSUES - MALE-SPECIFIC ISOFORMS ARE EXPRESSED IN THE GONADS AND LIVER/, Endocrinology, 133(1), 1993, pp. 39-45
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
.