It has long been recognized that individual cell types within the testes possess the capacity to synthesize
estrogen. A number of studies on different species have demonstrated that the levels of
aromatase expression and the patterns of regulation are distinct between the different cell types of the testes. Whereas a variety of promoters have been shown to contribute to the patterns of
aromatase expression in different cell lineages, studies using ovarian
RNA, testis
RNA, and
Leydig cell tumor lines have demonstrated that the same promoter (promoter II) was used in each. Recent experiments using potent
aromatase inhibitors or analysis of animals in which the genes encoding the
estrogen receptor-alpha (ER-alpha) or the
aromatase, P450, are defective, have confirmed the importance of local
estrogen formation in normal testicular function. In order to permit experiments to identify the elements controlling
aromatase expression in the individual cell compartments of the testes, we prepared
RNA from purified preparations of Leydig, Sertoli, and germ cells. Using specific
oligonucleotide primers, the sites of initiation of the
aromatase mRNA were determined using rapid amplification of
cDNA ends (RACE) and nucleotide sequence analysis of the resulting
cDNA fragments. Our results indicate that
aromatase mRNA is derived from the proximal promoter (PII) of the
aromatase gene in each of the major cell types of the rat testes.