The testicular feminized (Tfm) mouse lacks functional androgen receptors and develops with a female external phenotype and internal testes. The testes of these animals contain normal, or close to normal, numbers of Leydig cells but secrete very low amounts of androgen due to a lack of 17α-hydroxylase activity. To determine whether this loss of activity is due to a lack of enzyme synthesis or a change in catalytic activity we have examined 17α-hydroxylase cytochrome P-450 (P-45017α) protein and mRNA levels in the testes of Tfm mice.
Levels of P-45017α protein were measured by immunoblotting, while mRNA was measured following reverse transcription (RT) and amplification by the polymerase chain reaction (PCR). Conditions for RT-PCR were determined which allowed semiquantification of P-45017α mRNA relative to β-actin mRNA. In extracts of Tfm testes P-45017α protein was undetectable using antiserum against porcine P-45017α. In contrast, a protein of around 54 kDa was clearly detectable in extracts of control cryptorchid testes. Using RT-PCR, P-45017α mRNA was detectable in both control and [ill] testes but, expressed in terms of β-actin mRNA, levels of P-45017α mRNA in control testes were 40-fold higher than those in [ill] testes. If the total amount of RNA extracted from each testis is taken into account then P-45017α mRNA levels per testis were up to 400-fold higher in control testes. These results show that the reduced level of 17α-hydroxylase activity in [ill] testes is related to reduced protein synthesis. Previous results have shown that androgens reduce P-45017α mRNA levels in cultured Leydig cells. Results from this study suggest, however, that androgens are required to induce normal levels of P-45017α mRNA in Leydig cells.
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