Functional genome analysis indicates loss of 17beta-hydroxysteroid dehydrogenase type 2 enzyme in the zebrafish

Characterization and Functional Analysis of the 17-Beta Hydroxysteroid Dehydrogenase 2 (hsd17b2) Gene during Sex Reversal in the Ricefield Eel (Monopterus albus)

In mammals, 17-beta hydroxysteroid dehydrogenase 2 (Hsd17b2) enzyme specifically catalyzes the oxidation of the C17 hydroxyl group and efficiently regulates the activities of estrogens and androgens to prevent diseases induced by hormone disorders. However, the functions of the hsd17b2 gene involved in animal sex differentiation are still largely unclear. The ricefield eel (Monopterus albus), a protogynous hermaphroditic fish with a small genome size (2n = 24), is usually used as an ideal model to study the mechanism of sex differentiation in vertebrates. Therefore, in this study, hsd17b2 gene cDNA was cloned and its mRNA expression profiles were determined in the ricefield eel. The cloned cDNA fragment of hsd17b2 was 1230 bp, including an open reading frame of 1107 bp, encoding 368 amino acid residues with conserved catalytic subunits. Moreover, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis showed that hsd17b2 mRNA expressed strongly in the ovaries at early developmental stages, weakly in liver and intestine, and barely in testis and other tissues. In particular, hsd17b2 mRNA expression was found to peak in ovaries of young fish and ovotestis at the early stage, and eventually declined in gonads from the late ovotestis to testis. Likewise, chemical in situ hybridization results indicated that the hsd17b2 mRNA signals were primarily detected in the cytoplasm of oogonia and oocytes at stage I-II, subsequently concentrated in the granulosa cells around the oocytes at stage Ⅲ-Ⅳ, but undetectable in mature oocytes and male germ cells. Intriguingly, in ricefield eel ovaries, hsd17b2 mRNA expression could be significantly reduced by 17β-estradiol (E2) or tamoxifen (17β-estradiol inhibitor, E2I) induction at a low concentration (10 ng/mL) and increased by E2I induction at a high concentration (100 ng/mL). On the other hand, both the melatonin (MT) and flutamide (androgen inhibitor, AI) induction could significantly decrease hsd17b2 mRNA expression in the ovary of ricefield eel. This study provides a clue for demonstrating the mechanism of sexual differentiation in fish. The findings of our study imply that the hsd17b2 gene could be a key regulator in sexual differentiation and modulate sex reversal in the ricefield eel and other hermaphroditic fishes.

Molecular characterization and expression profiling of 17-beta-hydroxysteroid dehydrogenase 2 and spermatogenesis associated protein 2 genes in endangered catfish, Clarias magur (Hamilton, 1822)

The 17-beta-hydroxysteroid dehydrogenase 2 (17β-HSD2) enzyme regulates steroid levels by the inactivation of estrogen and androgens. Spermatogenesis associated protein 2 (SPATA2) plays a vital role in spermatogenesis in vertebrates including fish. We report cloning and characterization of full cds of 17β-HSD2 and SPATA2 genes in Clarias magur. The full-length cDNA sequences of 17β-HSD2 and SPATA2 were 1187 bp (ORF 1125 bp) and 1806 bp (ORF 1524 bp) encoding 375 and 508 amino acids, respectively. Signal peptide analysis revealed SPATA2 is nonsecretory, while 17β-HSD2 is a secretory protein. Hydropathy profiles showed both proteins are hydrophilic in nature. Tissue distribution of both the genes revealed high mRNA level of SPATA2 in all tissues examined indicating its wide range of expression. 17β-HSD2 indicated higher expression in preparatory phase compared to spawning phase in ovary while it was opposite in case of testis. SPATA2 showed significantly higher expression in preparatory phase compared to spawning phase in both ovary and testis. Administration of Ovatide^TM (GnRH analog) resulted in upregulation of SPATA2 expression at 6 and 16 h post-injection while 17β-HSD2 showed upregulation only at 6 h post-injection. To the best of our knowledge, this is a first report on characterization of 17β-HSD2 and SPATA2 full-length cDNA in catfish.

Absence of 11-keto reduction of cortisone and 11-ketotestosterone in the model organism zebrafish

Zebrafish are widely used as model organism. Their suitability for endocrine studies, drug screening and toxicity assessements depends on the extent of conservation of specific genes and biochemical pathways between zebrafish and human. Glucocorticoids consist of inactive 11-keto (cortisone and 11-dehydrocorticosterone) and active 11β-hydroxyl forms (cortisol and corticosterone). In mammals, two 11β-hydroxysteroid dehydrogenases (11β-HSD1 and 11β-HSD2) interconvert active and inactive glucocorticoids, allowing tissue-specific regulation of glucocorticoid action. Furthermore, 11β-HSDs are involved in the metabolism of 11-oxy androgens. As zebrafish and other teleost fish lack a direct homologue of 11β-HSD1, we investigated whether they can reduce 11-ketosteroids. We compared glucocorticoid and androgen metabolism between human and zebrafish using recombinant enzymes, microsomal preparations and zebrafish larvae. Our results provide strong evidence for the absence of 11-ketosteroid reduction in zebrafish. Neither human 11β-HSD3 nor the two zebrafish 11β-HSD3 homologues, previously hypothesized to reduce 11-ketosteroids, converted cortisone and 11-ketotestosterone (11KT) to their 11β-hydroxyl forms. Furthermore, zebrafish microsomes were unable to reduce 11-ketosteroids, and exposure of larvae to cortisone or the synthetic analogue prednisone did not affect glucocorticoid-dependent gene expression. Additionally, a dual-role of 11β-HSD2 by inactivating glucocorticoids and generating the main fish androgen 11KT was supported. Thus, due to the lack of 11-ketosteroid reduction, zebrafish and other teleost fish exhibit a limited tissue-specific regulation of glucocorticoid action, and their androgen production pathway is characterized by sustained 11KT production. These findings are of particular significance when using zebrafish as a model to study endocrine functions, stress responses and effects of pharmaceuticals.

Clinical Chemistry and Other Laboratory Tests on Mouse Plasma or Serum

Besides hematological analyses, many other parameters, including clinical chemistry and endocrinological values, can be determined from mouse blood samples. For most of these tests, plasma or serum samples are used. Data obtained by these investigations provide indications of genotype effects on metabolism and organ functions. Here we describe in detail the considerations that have to be taken into account to get adequate samples for plasma or serum analyses and the recommended sample processing for different investigations. Furthermore, we describe established methods used in the German Mouse Clinic (GMC) to determine clinical chemical parameters; for more in-depth analysis of specific classes of biomarkers, we provide instructions for ELISAs (sandwich and competitive) as well as LC-MS/MS, focusing on markers associated with bone or steroid metabolism in the mouse as working examples. Curr. Protoc. Mouse Biol. 3:69-100 © 2013 by John Wiley & Sons, Inc.

Discovery of a novel enzyme mediating glucocorticoid catabolism in fish: 20beta-hydroxysteroid dehydrogenase type 2

Hydroxysteroid dehydrogenases (HSDs) are involved in metabolism and pre-receptor regulation of steroid hormones. While 17beta-HSDs and 11beta-HSDs are extensively studied in mammals, only few orthologs are characterized in fish. We discovered a novel zebrafish HSD candidate closely related to 17beta-HSD types 3 and 12, which has orthologs in other species. The enzyme catalyzes the conversion of cortisone to 20beta-hydroxycortisone identified by LC-MS/MS. We named the new enzyme 20beta-HSD type 2. All 20beta-HSD type 2 orthologs localize in the endoplasmic reticulum. Zebrafish 20beta-HSD type 2 is expressed during embryonic development showing the same expression pattern as 11beta-HSD type 2 known to oxidize cortisol to cortisone. In adult tissues 20beta-HSD type 2 shows a ubiquitous expression pattern with some minor sex-specific differences. In contrast to other enzymes metabolizing C21-steroids and being mostly involved in reproduction we propose that novel type 2 20beta-HSDs in teleost fish are important enzymes in cortisol catabolism.

The brain of teleost fish, a source, and a target of sexual steroids

Neurosteroids are defined as steroids de novo synthesized in the central nervous system. While the production of neurosteroids is well documented in mammals and amphibians, there is less information about teleosts, the largest group of fish. Teleosts have long been known for their high brain aromatase and 5α-reductase activities, but recent data now document the capacity of the fish brain to produce a large variety of sex steroids. This article aims at reviewing the available information regarding expression and/or activity of the main steroidogenic enzymes in the brain of fish. In addition, the distribution of estrogen, androgen, and progesterone nuclear receptors is documented in relation with the potential sites of production of neurosteroids. Interestingly, radial glial cells acting as neuronal progenitors, appear to be a potential source of neurosteroids, but also a target for centrally and/or peripherally produced steroids.

Hydroxysteroid (17{beta}) dehydrogenase 12 is essential for mouse organogenesis and embryonic survival

Hydroxysteroid (17beta) dehydrogenases (HSD17Bs) have a significant role in steroid metabolism by catalyzing the conversion between 17-keto and 17beta-hydroxysteroids. However, several studies in vitro have shown that some of these enzymes may also be involved in other metabolic pathways. Among these enzymes, HSD17B12 has been shown to be involved in both the biosynthesis of estradiol and the elongation of the essential very long fatty acids in vitro and in vivo. To investigate the function of mammalian HSD17B12 in vivo, we generated mice with a null mutation of the Hsd17b12 gene (HSD17B12KO mice) by using a gene-trap vector, resulting in the expression of the lacZ gene of the trapped allele. The beta-galactosidase staining of the heterozygous HSD17B12KO mice revealed that Hsd17b12 is expressed widely in the embryonic day (E) 7.5-E9.5 embryos, with the highest expression in the neural tissue. The HSD17B12KO mice die at E9.5 at latest and present severe developmental defects. Analysis of the knockout embryos revealed that the embryos initiate gastrulation, but organogenesis is severely disrupted. As a result, the E8.5-E9.5 embryos were void of all normal morphological structures. In addition, the inner cell mass of knockout blastocysts showed decreased proliferation capacity in vitro, and the amount of arachidonic acid was significantly decreased in heterozygous HSD17B12 ES cells. This, together with the expression pattern, suggests that in mouse, the HSD17B12 is involved in the synthesis of arachidonic acid and is essential for normal neuronal development during embryogenesis.

Aromatase in the brain of teleost fish: expression, regulation and putative functions

Unlike that of mammals, the brain of teleost fish exhibits an intense aromatase activity due to the strong expression of one of two aromatase genes (aromatase A or cyp19a1a and aromatase B or cyp19a1b) that arose from a gene duplication event. In situ hybridization, immunohistochemistry and expression of GFP (green fluorescent protein) in transgenic tg(cyp19a1b-GFP) fish demonstrate that aromatase B is only expressed in radial glial cells (RGC) of adult fish. These cells persist throughout life and act as progenitors in the brain of both developing and adult fish. Although aromatase B-positive radial glial cells are most abundant in the preoptic area and the hypothalamus, they are observed throughout the entire central nervous system and spinal cord. In agreement with the fact that brain aromatase activity is correlated to sex steroid levels, the high expression of cyp19a1b is due to an auto-regulatory loop through which estrogens and aromatizable androgens up-regulate aromatase expression. This mechanism involves estrogen receptor binding on an estrogen response element located on the cyp19a1b promoter. Cell specificity is achieved by a mandatory cooperation between estrogen receptors and unidentified glial factors. Given the emerging roles of estrogens in neurogenesis, the unique feature of the adult fish brain suggests that, in addition to classical functions on brain sexual differentiation and sexual behaviour, aromatase expression in radial glial cells could be part of the mechanisms authorizing the maintenance of a high proliferative activity in the brain of fish.

Zebrafish 17beta-hydroxysteroid dehydrogenases: an evolutionary perspective

The term 17beta-hydroxysteroid dehydrogenase (17beta-HSD) describes an enzyme that stereospecifically reduces or oxidizes a keto- or hydroxy group at C17 of the steroid scaffold, respectively. Fourteen mammalian 17beta-HSDs have been identified so far and nine sequence homologs are found in zebrafish. 17beta-HSDs additionally active in fatty acid metabolism display high sequence conservation and widespread tissue expression. Homologs of these multifunctional 17beta-HSDs have been identified in flies, worms and yeast, and steroid-converting activity was demonstrated in some cases. The "classical" 17beta-HSDs, types 1, 2 and 3, are steroid-specific enzymes expressed in few tissues. They may have arisen at the beginning of vertebrate evolution allowing new, differently controlled modes of steroid hormone action. These findings reflect on two aspects: (1) the evolutionary origin of steroid-specific enzymes and (2) a possible conservation of steroid hormone function in invertebrates through currently unknown mechanisms.

Recent advances in 17beta-hydroxysteroid dehydrogenases

The metabolism of steroids at position 17 is catalysed by a growing number of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs). Several human diseases like breast or prostate cancer, endometriosis,metabolic syndrome and mental diseases were associated with dysfunctions of 17beta-HSDs, which consequently became drug targets. This review will focus on identities of 17beta-HSDs and recent advances in analyses of their physiological roles in steroid and lipid metabolism. It will also address the potential of metabolomics in drug development.

Human and zebrafish hydroxysteroid dehydrogenase like 1 (HSDL1) proteins are inactive enzymes but conserved among species

Hydroxysteroid dehydrogenase like 1 protein (HSDL1) is an uncharacterized member of short-chain dehydrogenase/reductase (SDR) protein family. In search for functional assignment of both human and zebrafish HSDL1 we characterized the subcellular localization as well as the tissue distribution and performed a screen for putative substrates of HSDL1 enzymes. Surprisingly, human HSDL1 shows exchange of an amino acid in the active center (Sx(12)FSxxK instead of Sx(12)YSxxK) that is considered critical for catalysis. Native human HSDL1 expressed in cells did not show enzymatic activity with any of the substrates tested. Expression of the point mutation F218Y HSDL1 though, resulted in the detection of weak dehydrogenase activity towards steroid and retinoid substrates. The role of this inactivating mutation is uncertain but was found to be conserved in many other vertebrate species, including zebrafish. Identification of protein interaction partners by yeast two-hybrid system suggests that despite the potential lack of enzymatic activity HSDL1 might retain regulatory functions in the cell.

RDH12, a retinol dehydrogenase causing Leber's congenital amaurosis, is also involved in steroid metabolism

Three retinol dehydrogenases (RDHs) were tested for steroid converting abilities: human and murine RDH 12 and human RDH13. RDH12 is involved in retinal degeneration in Leber's congenital amaurosis (LCA). We show that murine Rdh12 and human RDH13 do not reveal activity towards the checked steroids, but that human type 12 RDH reduces dihydrotestosterone to androstanediol, and is thus also involved in steroid metabolism. Furthermore, we analyzed both expression and subcellular localization of these enzymes.