Volume 51 (11): 1425-1436, 2003 Copyright ©The Histochemical Society, Inc.
Sex-related Expression of 20
Oncology and Molecular Endocrinology Research Center, Laval University Medical Center (CHUL) and Laval University, Québec, (PQ) Canada Correspondence to: Dr. Georges Pelletier, Oncology and Molecular Endocrinology Research Center and Québec Génome Center, Laval University Hospital (CHUL), 2705 Laurier Boulevard. Québec, PQ G1V 4G2, Canada. E-mail: georges.pelletier{at}crchul.ulaval.ca
The enzyme 20 -hydroxysteroid dehydrogenase (20 -HSD) catalyzes the conversion of progesterone into its inactive form, 20 -hydroxyprogesterone. To gain information about the exact sites of 20 -HSD mRNA expression, we performed in situ hybridization using a 35S-labeled cRNA probe in tissues of adult mice of both sexes. 20 -HSD mRNA was expressed in both male and female gonads. In the ovary, high expression was found in luteal cells of corpora lutea, while much lower expression could be detected in granulosa cells of growing follicles. In the testis, a specific hybridization signal was detected only in Leydig cells. In the female reproductive tract, 20 -HSD mRNA was found in the epithelial cells of the uterine cervix. In the adrenal cortex, only the zona reticularis exhibited specific radiolabeling, the expression being very high in the female and very low in the male. In the skin, specific labeling was restricted to sebaceous glands, the hybridization signal being much higher in the female than in the male. In the liver, 20 -HSD mRNA was found in hepatocytes, with a higher degree of expression in the female. In the kidney, specific labeling was observed in the epithelial cells of distal convoluted tubules, the signal being also much more striking in the female than in the male. In non-reproductive tissues, it clearly appears that the expression of 20 -HSD mRNA is higher in the female than in the male, suggesting that 20 -HSD may play an important role in reducing the intracellular concentration of progesterone originating from the circulation at a much higher level in the female. (J Histochem Cytochem 51:14251436, 2003)
Key Words: progesterone catabolism 20
THE CONCENTRATION of active steroids is modulated in peripheral tissues by steroid-forming and steroid-inactivating enzymes. The enzyme 20 -hydroxysteroid dehydrogenase (20 -HSD) converts progesterone into its inactive form, 20 -hydroxyprogesterone. Its role is particularly important in the ovary because it induces luteolysis (Strauss et al. 1972 -HSD is probably involved in regulating the amount of progesterone that can bind to progesterone receptors. Recently, the cDNAs encoding rat and rabbit ovarian, bovine testicular, and human skin 20 -HSD have been cloned (Lacy et al. 1993 -HSD from different species belongs to the aldoketo reductase family. In the rat, 20 -HSD mRNA was highly expressed in the ovary, whereas it was almost undetectable in the uterus, kidney, lung and heart (Mao et al. 1994 -HSD mRNA has been observed in the liver, mammary gland, and brain, whereas low expression has been detected in the prostate, testis, adrenal, uterus, and keratinocytes (HaCaT) (Zhang et al. 2000 -HSD expression has also been detected by RT-PCR (RumkeVogl et al. 2002
Thus far, the precise localization of 20
Animals Four adult male (2630 g) and female (2427 g) C57BL6 mice were housed under constant temperature (21 ± 1C) and light (lights on from 0600 to 2000 hr) regimen. The animals received Purina Chow (Ralston-Purina; St Louis, MO) and tapwater ad libitum. The experiment was conducted in an animal facility approved by the Canadian Council on Animal Care (CCAC) and by the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC). The study was performed in accordance with the CCAC Guide for Care and Use of Experimental Animals. The animals were all perfused between 0900 and 1000 hr for histological procedures as described below. The females were on diestrous day 1.
Histological Procedures
In Situ Hybridization After hybridization, coverslips were removed and slides were rinsed in 2 x SSC at RT for 30 min. Sections were digested by RNase A (20 µg/ml in 2 x SSC) at 37C for 30 min, rinsed in decreasing concentrations of SSC (2 x SSC and 1 x SSC) for 30 min at RT, washed in 0.5 x SSC for 30 min at 37C, followed by 90 min at RT in 0.5 x SSC, at 60C in 0.1 x SSC, and finally for 30 min at RT in 0.1 x SSC. The sections were then dehydrated and exposed to Kodak Biomax MR films for 38 days before being coated with liquid photographic emulsion (Kodak-NTB2; diluted 1:1 with water). Slides were exposed for 145 days, developed in Dektol developer (Kodak; Rochester, NY) for 2 min, and fixed in rapid fixer (Kodak) for 4 min. Thereafter, tissues were rinsed in running water for 30 min, counterstained with hematoxylin, and rapidly dehydrated through graded concentrations of ethanol, cleared in toluene, and coverslipped with Permount (Fisher Scientific; Montreal, PQ, Canada).
After 38-day exposure of the films, specific labeling was found in the ovary, uterine cervix, mammary gland, testis, skin, adrenal cortex, liver, and kidney. No specific hybridization signal could be detected in the vagina, prostate, pituitary, jejunum, and pancreas. From photographic emulsion-coated sections, information could be obtained about the cell types expressing 20 -HSD mRNA in the different tissues. In the ovary, as shown in X-ray films and emulsion-coated slides after a short exposure time (7 days), labeling was restricted to corpora lutea (Figures 1 and 2)
. Because the mice were in diestrous day 1, only old corpora lutea were present. Cell counting performed on at least two corpora lutea per ovary (four mice) established that approximately 30% of luteal cells were labeled. At longer exposure times (28 days), weak specific labeling was also observed in granulosa cells of growing follicles at all stages of development (Figure 3)
.
In the uterine cervix, the hybridization signal was found in both endocervix and exocervical epithelial cells, the stroma being devoid of any specific labeling (Figure 4) . In the female mouse mammary gland, weak specific labeling was restricted to stromal cells surrounding ducts (Figure 5) . Typical acini could not be observed. In the male mouse mammary gland, no specific labeling could be detected in any cell type at the longest time interval studied (45 days). In the testis, a specific hybridization signal was found only over Leydig cells, the tubules being devoid of any specific reaction (Figure 6) .
In female adrenal glands, strong labeling was obtained in the zona reticularis of the adrenal cortex as early as after 1 day of exposure time, whereas the other zones of the cortex and the adrenal medulla were totally negative (Figure 7A) . In the male, only weak labeling could be detected in the zona reticularis of the adrenal cortex after the longest exposure time (45 days) (Figure 7B).
In the female mouse skin, a specific hybridization signal was detected in the sebaceous gland cells after 7 days of exposure (Figure 8) , but the epidermis, stromal cells, and hair follicles were totally unlabeled. In the male, only a weak signal could be obtained in the sebaceous glands after a long-term exposure (not shown). In the liver, 20 -HSD mRNA appeared to be expressed in both male and female animals, with a higher signal in the female (Figure 9)
. As observed by light microscopy, specific labeling was detected in all the hepatocytes (Figure 10)
. In the kidney, specific labeling was observed in a large area located between the medulla and the outer part of the cortex (Figure 11)
. As observed for the other tissues, the expression of the enzyme mRNA was higher in the female than in the male (Figure 11). At the light microscopic level, we observed that silver grains were overlying the epithelial cells lining the distal convoluted tubules, whereas the glomeruli, proximal convoluted tubules, collecting tubules, and blood vessels were unlabeled (Figure 12)
. In all the tissues examined, hybridization with the sense probe generated only a light uniform labeling (for examples, see Figures 1, 2, 4, 5, 6, 8, 10, and 12).
The enzyme 20 -HSD plays an important role in the regulation of the intracellular concentration of progesterone. Cloning of the cDNA encoding mouse 20 -HSD has allowed studies on the histological localization of 20 -HSD mRNA in a series of male and female mouse tissues. In the ovary, strong labeling was observed in about 30% of luteal cells in corpora lutea, while a much weaker signal was obtained in granulosa cells of growing follicles. These findings support the data indicating that, in the rat ovary, 20 -HSD activity was much higher in luteal than in non-luteal cells (Seong et al. 1992 -HSD plays a pivotal role in the regulation of progesterone secretion by corpora lutea. It is generally admitted, however, that there are two types of luteal cells: the luteinizing granulosa cells, which have a large cytoplasm with small lipid droplets, and the theca lutein cells, which are smaller but contain large lipid droplets. It was not possible using frozen sections to establish which luteal cell type(s) was involved in 20 -HSD mRNA expression. On the other hand, it has been shown that, in the rat ovary, all the luteal cells express the enzyme 3ß-hydroxysteroid dehydrogenase and can therefore be involved in progesterone secretion (Dupont et al. 1990 -HSD, thus contributing to maintenance of progesterone at high levels during pregnancy (Albarracin et al. 1994 -HSD weakly expressed in granulosa cells remains to be clarified.
In the female reproductive tract, 20
In the mammary gland of the female mouse, weak 20
In the mouse testis, the hybridization signal was observed only in Leydig cells. The testicular localization of the enzyme has already been reported in the bovine and human species (Warren et al. 1993
In the adrenal glands, 20
In the skin, 20
In the kidney, a specific hybridization signal was found in the epithelial cells in the distal convoluted tubules. As in other tissues, the signal was more striking in the female than in the male. In the human kidney, the expression of 20
The absence of any hybridization signal in the prostate, uterus, vagina, and pituitary might be explained by a low expression of 20
In summary, the present results on the localization of 20
The ATLAS program was supported by Genome Canada and Genome Québec.
Received for publication April 14, 2003; accepted July 10, 2003
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