Two isoforms of FTZ-F1 messenger RNA: molecular cloning and their expression in the frog testis

Sex-specific splicing of Z- and W-borne nr5a1 alleles suggests sex determination is controlled by chromosome conformation

Pogona vitticeps has female heterogamety (ZZ/ZW), but the master sex-determining gene is unknown, as it is for all reptiles. We show that nr5a1 (Nuclear Receptor Subfamily 5 Group A Member 1), a gene that is essential in mammalian sex determination, has alleles on the Z and W chromosomes (Z-nr5a1 and W-nr5a1), which are both expressed and can recombine. Three transcript isoforms of Z-nr5a1 were detected in gonads of adult ZZ males, two of which encode a functional protein. However, ZW females produced 16 isoforms, most of which contained premature stop codons. The array of transcripts produced by the W-borne allele (W-nr5a1) is likely to produce truncated polypeptides that contain a structurally normal DNA-binding domain and could act as a competitive inhibitor to the full-length intact protein. We hypothesize that an altered configuration of the W chromosome affects the conformation of the primary transcript generating inhibitory W-borne isoforms that suppress testis determination. Under this hypothesis, the genetic sex determination (GSD) system of P. vitticeps is a W-borne dominant female-determining gene that may be controlled epigenetically.

TAF10 and TAF10b partially redundant roles during Drosophila melanogaster morphogenesis

Transcription of eukaryotic genes requires the cooperative action of the RNA polymerase complex, the general transcription factors (TFIIB, TFIID, TFIIE, TFIIF and TFIIH) and chromatin modifiers. The TFIID complex contributes to transcriptional activation by several mechanisms and has a subunit with associated histone acetyltransferase (HAT) activity. The histone modifier SAGA complex has both HAT and deubiquitylase (DUB) activities. TFIID and SAGA share several TBP-associated factors (TAFs), but not their HAT subunit. Recently, several duplicated TAF proteins have been identified in higher eukaryotes, but their functional diversity has been so far poorly characterized. Here, we report the functional similarities and differences of TAF10 and TAF10b, the two TAF10 orthologs of Drosophila melanogaster. Results from in silico modeling suggest that dTAF10 and dTAF10b have similar secondary structures characterized by the presence of a histone-fold domain. Additionally, dTAF10 and dTAF10b share interaction partners and show similar expression patterns in neuronal tissues. Nonetheless, dTAF10 and dTAF10b seem to have partly distinct functions. To investigate their roles, we generated dTaf10-dTaf10b double-mutants and rescued the mutant flies with transgenes, which allowed the translation of either dTAF10 or dTAF10b protein. We found that the loss of dTAF10b resulted in pupal lethality, while animals lacking dTAF10 were able to form puparium. dTaf10 mutant adults showed distorted eye morphology. During DNA repair, dTAF10 and dTAF10b act redundantly, suggesting that these proteins have distinct but partially overlapping functions.

Sexually Dimorphic Expression of Foxl2 and Ftz-F1 in Chinese Giant Salamander Andrias Davidianus

Foxl2 and FTZ-F1 play a crucial role in the regulation of gonad development in fish and mammals, but studies of their function in amphibians are scarce. We isolated the full length of Foxl2 (adFoxl2) and Ftz-F1 (adFtz-f1) cDNA from the Chinese giant salamander Andrias davidianus and quantified its expression in various tissues and developing gonads. The adFoxl2 gene encodes 301aa including a conserved forkhead box, and the adFtz-f1 gene encodes 467aa containing an Ftz-F1 box. The amino acid sequences showed high homology with other amphibians. adFoxl2 expression was high in ovary, whereas adFtz-f1 was higher in testis, moderate in pituitary, ovary, and kidney; and low in the remaining tested tissues. Expression of adFoxl2 gradually increased from 1Y to 5Y in ovary, whereas adFtz-f1 expression gradually decreased in testis. In addition, adFoxl2 and adFtz-f1 were detected in granulosa cell in ovary and in spermatocytes in testis. The adFoxl2 transcription was inhibited in brain and ovary after treatment with methyltestosterone and with letrozole, whereas adFtz-f1 expression was upregulated. High-temperature suppressed the expression of adFxl2 in ovary and enhanced the transcription of adFtz-f1. These results suggest that adFoxl2 functioned in ovary differentiation, whereas adFtz-f1 played a role in testis development, which lays a foundation for study of the sex differentiation mechanism in A. davidianus.

Molecular cloning and expression analysis of fushi tarazu factor 1 in the brain of air-breathing catfish, Clarias gariepinus

Background

Fushi tarazu factor 1 (FTZ-F1) encodes an orphan nuclear receptor belonging to the nuclear receptor family 5A (NR5A) which includes adrenal 4-binding protein or steroidogenic factor-1 (Ad4BP/SF-1) and liver receptor homologue 1 (LRH-1) and plays a pivotal role in the regulation of aromatases.

Methodology/Principal Findings

Present study was aimed to understand the importance of FTZ-F1 in relation to brain aromatase (cyp19a1b) during development, recrudescence and after human chorionic gonadotropin (hCG) induction. Initially, we cloned FTZ-F1 from the brain of air-breathing catfish, Clarias gariepinus through degenerate primer RT-PCR and RACE. Its sequence analysis revealed high homology with other NR5A1 group members Ad4BP/SF-1 and LRH-1, and also analogous to the spatial expression pattern of the latter. In order to draw functional correlation of cyp19a1b and FTZ-F1, we analyzed the expression pattern of the latter in brain during gonadal ontogeny, which revealed early expression during gonadal differentiation. The tissue distribution both at transcript and protein levels revealed its prominent expression in brain along with liver, kidney and testis. The expression pattern of brain FTZ-F1 during reproductive cycle and after hCG induction, in vivo was analogous to that of cyp19a1b shown in our earlier study indicating its involvement in recrudescence.

Conclusions/Significance

Based on our previous results on cyp19a1b and the present data, it is plausible to implicate potential roles for brain FTZ-F1 in ovarian differentiation and recrudescence process probably through regulation of cyp19a1b in teleosts. Nevertheless, these interactions would require primary coordinated response from ovarian aromatase and its related transcription factors.

Differential display analysis of gene expression in female-to-male sex-reversing gonads of the frog Rana rugosa

Sex steroids play pivotal roles in gonadal differentiation in many species of vertebrates. The sex can be reversed from female to male by testosterone in the Japanese wrinkled frog Rana rugosa, but it is still unclear what genes are up- or down-regulated during the XX sex-reversal in this species. To search the genes for the female-to-male sex-reversal, we employed differential display and 5'/3'-RACE. Consequently, we isolated from the gonads at day 8 after testosterone injection 24 different cDNA fragments showing a testosterone treatment-related change and then obtained three full-length cDNAs, which we termed Zfp64, Zfp112, and Rrp54. The former two cDNAs encoded different proteins with zinc-finger domains, whereas the latter cDNA encoded an unknown protein. Transcripts of the three genes were hardly detectable in the sex-reversing gonads at day 24 after the injection; at this time few growing oocytes were observed in the sex-reversing gonad. Besides, in situ hybridization analysis showed positive signals of the three genes in the cytoplasm of growing oocytes of an ovary when testosterone was injected into a tadpole. Thus, the decrease in expression of these three genes was probably due to the disappearance of growing oocytes and not to their direct involvement in the testis formation. To find the key-gene for testis formation, it will be necessary to analyze, by the differential display method, more genes showing a change in expression pattern during sex reversal.

Elevated expression of P450c17 (CYP17) during testicular formation in the frog

Sex steroids play decisive roles in gonadal differentiation in many species of vertebrates. The sex can be changed by sex steroids in some species of amphibians, but the mechanism of the sex-reversal is largely unknown. In this study, we cloned and characterized 3 cDNAs encoding sex steroid-synthesizing enzymes, i.e., CYP11A1, CYP17 and 3beta-HSD from the frog Rana rugosa. RT-PCR analysis showed that the CYP17 expression was much higher in male gonads than in female ones during sex determination in R. rugosa, whereas CYP11A1 and 3beta-HSD showed no sexually dimorphic expression. When testosterone was injected into tadpoles for female-to-male sex reversal, CYP17 expression appeared to be very strong in the gonad at days 16 and 24 after injection of testosterone. CYP11A1 was also transcribed higher at day 16, but its expression was weaker when compared with that of CYP17. The expression of 3beta-HSD did not change during the sex reversal. In addition, in situ hybridization analysis revealed that CYP17 was expressed in somatic cells of the indifferent male gonad and in those of the testis. Positive signals of CYP17 were also produced in somatic cells of a female-to-male sex-reversed gonad (testis) at days 16 and 24 post testosterone injection, but not in the ovary. Taken together, the results suggest that CYP17 is very involved in testicular differentiation of the gonad in R. rugosa.

Molecular cloning and expression in gonad of Rana rugosa WT1 and Fgf9

Sry (sex-determining region on the Y chromosome) is required for testicular differentiation in mammals. In addition to Sry, other genes such as WT1, Fgf9, Dax1, Dmrt1 and Sox9 are widely accepted to be involved in the sex determination in vertebrates. However, the roles of these genes during sex determination still remain unclear in amphibians. This study was undertaken to examine the expression of WT1 and Fgf9 in the developing gonad of amphibians. We first isolated the WT1 cDNA from the frog Rana rugosa. Like WT1 in mice, R. rugosa WT1 showed 2 isoforms; i.e., one had an additional 3 amino acids, KTS, included between the third and fourth zinc fingers. However, 17 amino acids in exon 5 of mammalian WT1 could not be found in R. rugosa WT1, which is also the case in turtle and chicken. The mRNA of both isoforms (+KTS, -KTS) was detected in the lung, kidney and testis, but not in the ovary and muscle of adult frogs. The 2 isoforms were expressed first in the embryos at stage 23. Thereafter, the expressions remained constant in the gonad attached to mesonephros of both sexes during sex determination. We next isolated the R. rugosa Fgf9 cDNA encoding 208 amino acids. The amino acid sequence of Fgf9 had similarity greater than 92% with chicken, mouse and human Fgf9s, suggesting that Fgf9 is highly conserved among vertebrate classes. Fgf9 was expressed in the ovary of an adult frog strongly, but in the lung weakly. In contrast, the Fgf9 mRNA was hardly detected in the kidney, testis and muscle. Moreover, Fgf9 did not show a sexually dimorphic expression pattern during sex determination in R. rugosa. The results, taken together, suggest that both WT1 and Fgf9 are expressed in the indifferent gonad prior to sex determination without any difference in the expression between males and females. Thus, it seems unlikely that they are a key factor to initiate the divergence leading to testicular or ovarian differentiation in R. rugosa.

Molecular cloning and tissue distribution of SF-1-related orphan receptors during sexual maturation in female goldfish

The steroidogenic factor (SF)-1 gene is one of a number of orphan nuclear receptors, which is a key transcriptional regulator in vertebrate reproduction. We have isolated the SF-1 homologue cDNA from the goldfish pituitary and designed primers for SF-1 on the basis of the highly conserved regions of various known SF-1 superfamily genes. SF-1 cDNA contained 1,948 nucleotides including an open reading frame predicted to encode a protein of 503 amino acids. The distribution pattern of SF-1 in a variety of tissues during sexual maturation in female goldfish was also examined by RT-PCR. Significant variations in the relative expression of SF-1 were observed in different tissues in immature and mature female goldfish. SF-1 transcript in pituitary was significantly higher than other tissues tested in immature and mature female goldfish. Lower expression of SF-1 was observed in the liver but was not detected in brain and ovary of the immature female goldfish. Presence of SF-1 was the predominant expression in the pituitary and brain of mature female goldfish. Also, in the mature female goldfish, a weak transcript was detected in liver and ovary. Interestingly, RT-PCR analysis revealed that the expression of SF-1 became higher in the brain and weaker in the liver in maturing female goldfish. Thus, SF-1 may be regulated in goldfish brain and/or liver. Thus is also tissue-specific distribution of SF-1 during sexual maturation in female goldfish.

Chicken LRH-1 gene is transcribed from multiple promoters in steroidogenic organs

Liver receptor homolog-1 (LRH-1) is a homolog of FTZ-F1, a transcription factor of the fruit fly, and belongs to the orphan nuclear receptor family. LRH-1 is expressed in organs derived from the endoderm, including intestine, liver and exocrine pancreas and plays a predominant role in development, bile-acid homeostasis, and reverse cholesterol transport. Recent research has revealed that mammalian LRH-1 is also expressed in the steroidogenic organs and has suggested that LRH-1 shares a role in steroidogenesis with steroidogenic factor-1 (SF-1), which is a paralog of LRH-1. In this study, we determined transcription initiation sites of chicken LRH-1 and showed that LRH-1 is expressed as several splicing variants in chicken steroidogenic organs. From three steroidogenic organs, the adrenal glands, ovaries, and testes, several cDNA fragments including different lengths and sequences were amplified by 5'-RACE and these were mainly classified into five types. Using these sequences, chicken genomic database was searched and four types of first exons were identified in chromosome 8. However, the database sequence of these regions included several gaps. So we cloned gap regions by PCR cloning from chicken genomic DNA and found the other type of first exons in the gaps. Moreover, RT-PCR showed the expression of LRH-1 in chicken steroidogenic organs as many splicing variants. We concluded that the chicken LRH-1 gene is transcribed from at least five different transcription initiation sites and alternative splicing produces several types of mRNA in steroidogenic organs.

Promoter Activity and Chromosomal Location of the Rana rugosa P450 Aromatase (CYP19) Gene

Sex is determined genetically in amphibians, but is reversed occasionally by steroid hormones. The phenotypic sex of some amphibian species can be reversed from male to female by estrogens. Estrogens, which are synthesized from testosterone irreversibly by the enzyme P450 aromatase (CYP19), are essential for ovarian development in vertebrates. CYP19 expression is reportedly regulated by steroidogenic factor-1 (SF-1), also designated as Ad4BP, in fish and mammals. However, it is unknown if this is also the case in amphibians. Thus, to elucidate the role of SF-1 in CYP19 gene expression in the gonad of amphibians, it is necessary to isolate and characterize the promoter region of the CYP19 gene of amphibians. For this purpose, we first cloned the promoter region of CYP19 from genomic DNA fragments of the frog Rana rugosa. As a result, a potential binding site of SF-1 was found in the region. When a luciferase promoter assay in HEK 293 cells was carried out to examine the ability of SF-1 as a transcriptional regulator, we found that R. rugosa SF-1 stimulated the expression of the CYP19 gene of the tilapia Oreochromis niloticus, but not that of the frogs R. rugosa and Xenopus laevis. RT-PCR analysis revealed that CYP19 mRNA was expressed at a higher level in the indifferent gonads of females than in those of males. This was also true to SF-1 mRNA In addition, FISH analysis showed that the CYP19 gene was located on chromosome 3 of R. rugosa. Taken together, our data suggest that CYP19, an autosomal gene, is expressed in the undifferentiated gonads to an extent greater in females than in males, but its expression probably is not regulated by SF-1 alone. Another factor(s) may be required if SF-1 promotes the expression of the CYP19 gene in R. rugosa as it does in fish and mammals.

LRH-1: an orphan nuclear receptor involved in development, metabolism and steroidogenesis

The liver receptor homolog-1 (LRH-1; NR5A2) and steroidogenic factor-1 (SF-1; NR5A1) are two orphan members of the Ftz-F1 subfamily of nuclear receptors. LRH-1 is expressed in tissues derived from endoderm, including intestine, liver and exocrine pancreas, as well as in the ovary. In these tissues, LRH-1 plays a predominant role in development, reverse cholesterol transport, bile-acid homeostasis and steroidogenesis. SF-1 expression is confined to steroidogenic tissues and the hypothalamo-pituitary-adrenal axis, where it is involved in the control of development, differentiation, steroidogenesis and sexual determination. In this article, we will review data concerning the structure, regulation and function of LRH-1. These data highlight structural similarities between LRH-1 and other Ftz-F1 members but also underscore important functional differences, assigning to LRH-1 a unique position among nuclear receptors.

cDNA cloning and mRNA expression of a FTZ-F1 homologue from the pituitary of the orange-spotted grouper, epinephelus coioides

A FTZ-F1 homologue was cloned from the pituitary cDNA library of the orange-spotted grouper. The full-length cDNA of the orange-spotted grouper FTZ-F1 spanned 1735 bp including a poly (A) tail. The open reading frame encodes a protein of 468 amino acids. Sequence analysis indicated that it had a structure typical of the orphan nuclear receptor superfamily, and the FTZ-F1 box, a characteristic of the FTZ-F1 family. Phylogenetic analysis indicated that the orange-spotted grouper FTZ-F1 was closely related to medaka FTZ-F1 and did not belong to either the SF-1/Ad4BP group or the LRH-1/FTF group. Virtual Northern Blot detected a major transcript of about 1.7 kb and a minor transcript of 2.2 kb of FTZ-F1 in the orange-spotted grouper pituitary gland. The expression of FTZ-F1 homologue gene in different tissues and during embryonic development of the orange-spotted grouper was determined using one-step RT-PCR coupled with Southern blot analysis. In addition to the pituitary gland, the orange-spotted grouper FTZ-F1 was also expressed in the hypothalamus, forebrain, heart, liver, kidney, and ovary. The stronger signal from the gel image indicated that the expression level of FTZ-F1 homologue gene was higher in the ovary of stage 3 than stage 2. During embryonic development, mRNA for the orange-spotted grouper FTZ-F1 homologue was present in newly fertilized eggs, but disappeared in embryos at 50 min post fertilization. The orange-spotted grouper FTZ-F1 homologue mRNA reappeared in embryos at 1.5 hr post fertilization. Its expression level was increased from late blastula to neurula stages. Taken together, results of the current study suggest that the orange-spotted grouper FTZ-F1 homologue exhibits characteristics indicative of both the LRH-1/FTF- and the SF-1/Ad4BP-like genes, and may also play important roles in the hypothalamus-pituitary-gonadal axis, cholesterol metabolism, and embryogenesis.

Sequence and expression of cytochrome P450 aromatase and FTZ-F1 genes in the protandrous black porgy (Acanthopagrus schlegeli)

In this study, a cDNA encoding cytochrome P450 aromatase (P450arom) was cloned from black porgy Acanthopagrus schlegeli ovary. The deduced amino acid sequence had high homology with ovarian P450arom of other teleost fish. Moreover, we partially cloned two FTZ-F1 homologues (asff1a and asff1b) from black porgy. Comparative sequence analysis grouped asff1a and asff1b in NR5A2 and NR5A4 clades, respectively. Among the various tissues tested, P450arom mRNA was highly expressed in the ovary and weakly in the brain and testis, asff1a was expressed in brain, liver, intestine, kidney, testis, and ovary, asff1b was expressed in brain, kidney, testis, and ovary. The transcript levels of P450arom, asff1a, and asff1b were measured in the ovary and testis of 1+ -year-old, 2+ -year-old, and 5+ -year-old black porgy. The transcript level of P450arom in the ovary of 2+ -year-old fish was significantly higher than those of 1+ -year-old and 5+ -year-old fish. The results suggest that P450arom gene may be involved in the mechanism of natural sex change of protandrous black porgy. No change in ovarian expression of asff1a or asff1b was observed among different ages. These results suggest that up-regulation of the transcript levels of P450arom during the course of natural sex change of black porgy was not regulated via FTZ-F1.

Expression of P450 aromatase protein in developing and in sex-reversed gonads of the XX/XY type of the frog Rana rugosa

Gonadal differentiation in some species of amphibians is sensitive to steroids. The phenotypic sex of XX/XY-type frogs such as Rana rugosa can be reversed from female to male by injection of testosterone into tadpoles, but little is known about the molecular mechanism of this sex reversal. To elucidate the mechanism of the sex differentiation, we examined the role of P450 aromatase (P450arom), an enzyme that converts testosterone to estrogen, during gonadal differentiation of amphibians. In this study, we first cloned a P450arom cDNA homolog of the frog R. rugosa and analyzed by RT-PCR its expression profile in developing and in female-to-male sex-reversed gonads. P450arom expression was observed in the gonad of tadpoles during ovarian differentiation and became much stronger in the developing ovary in which only immature oocytes were observed. However, its expression declined significantly in the ovary of frogs 2 months after metamorphosis, when oocytes were growing; and it was no longer seen in adult ovaries. By RT-PCR, we also examined the expression of P450arom and SF-1 (steroidogenic factor-1; the orphan nuclear receptor) in the female-to-male sex-reversed gonad. The level of P450arom mRNA was high in the ovary, but it declined rapidly after the injection of testosterone. In contrast, no change in the SF-1 (also known as Ad4BP) expression was observed. Moreover, to identify the type(s) of cells expressing P450arom protein, we performed immunostaining with an antibody against frog P450arom protein. Cells giving positive signals were observed around oocytes in the ovary of frogs 1 month after metamorphosis. They were identified as follicle cells by both light and electron microscopy. The results, taken together, indicate that P450arom protein is synthesized in follicle cells and that P450arom is very much involved in ovarian differentiation in R. rugosa.

Pancreatic-duodenal homeobox 1 regulates expression of liver receptor homolog 1 during pancreas development

Liver receptor homolog 1 (LRH-1) and pancreatic-duodenal homeobox 1 (PDX-1) are coexpressed in the pancreas during mouse embryonic development. Analysis of the regulatory region of the human LRH-1 gene demonstrated the presence of three functional binding sites for PDX-1. Electrophoretic mobility shift assays and chromatin immunoprecipitation analysis showed that PDX-1 bound to the LRH-1 promoter, both in cultured cells in vitro and during pancreatic development in vivo. Retroviral expression of PDX-1 in pancreatic cells induced the transcription of LRH-1, whereas reduced PDX-1 levels by RNA interference attenuated its expression. Consistent with direct regulation of LRH-1 expression by PDX-1, PDX-1(-/-) mice expressed smaller amounts of LRH-1 mRNA in the embryonic pancreas. Taken together, our data indicate that PDX-1 controls LRH-1 expression and identify LRH-1 as a novel downstream target in the PDX-1 regulatory cascade governing pancreatic development, differentiation, and function.

Change of the heterogametic sex from male to female in the frog

Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.

Role of aromatase and androgen receptor expression in gonadal sex differentiation of ZW/ZZ-type frogs, Rana rugosa

To elucidate the mechanisms of amphibian gonadal sex differentiation, we examined the expression of aromatase and androgen receptor (AR) mRNAs for days 17-31 after fertilization. The effects of inhibitors and sex steroid hormones were also examined. In ZZ males, expression of AR decreased after day 19, while aromatase expression was low throughout the sampling period. Males treated with 17beta-estradiol (E2) showed increasing aromatase expression after day 21, and formed ovaries. AR antagonist treatment also induced high-level aromatase expression and ovarian differentiation. In males co-treated with an aromatase inhibitor and E2, the undifferentiated gonads developed into testes despite high-level aromatase expression. Males treated with androgen and E2 before and during an estrogen sensitive period, respectively, also formed testes. In ZW females, AR expression persisted at a low-level, while aromatase expression increased after day 18. Short-term treatment with an aromatase inhibitor was ineffective in preventing ovarian differentiation, whereas long-term treatment resulted in testes developing from ovarian structure. Compared with the ZZ males and ZW females, WW females did not exhibit detectable expression of AR, suggesting that the active AR gene(s) itself, or a putative gene regulating AR gene expression, is located on Z chromosomes. From the time lag of aromatase expression between ZW females and ZZ males treated with E2 and the effect of AR antagonist, it was found that in males elevated AR expression suppresses aromatase expression directly or indirectly. Consequently, endogenous androgens, accumulated by blocking estrogen biosynthesis, induced testicular differentiation. The gonadogenesis of males is dependent on sex hormone, whereas that of females has evolved to hormone-independence.

Expression of FTZ-F1alpha in transgenic Xenopus embryos and oocytes

Fushi tarazu transcription factor-1 (FTZ-F1) was originally found as a regulator of fushi tarazu gene expression in Drosophila. The frog homologue (FTZ-F1alpha) and the 3.5 kb 5'-flanking region of the FTZ-F1alpha gene have been cloned, and it has been shown by reverse transcription-polymerase chain reaction that FTZ-F1alpha expression begins in embryos at stage 11 and becomes stronger after that. By in situ hybridization analysis, the FTZ-F1alpha mRNA was also found in immature frog oocytes. In this study, immunohistology revealed that the product of FTZ-F1alpha was localized in the cytoplasm of the immature oocyte. To analyze the promoter activity of the Rana rugosa FTZ-F1alpha gene, transgenic Xenopus were produced carrying the fusion construct, consisting of truncated 5'-flanking regions (3.0, 1.8 and 0.3 kb) of the FTZ-F1alpha gene and the green fluorescent protein (GFP) open reading frame. The 0.3 kb 5'-flanking region could drive GFP expression in Xenopus embryos at stage 20 and in immature oocytes in the ovary 2 months after metamorphosis. Gel mobility shift assay was used to test whether proteins in extracts from Xenopus embryos and ovaries bound to the 0.3 kb DNA. The extract from embryos at stage 11 formed one retarded band. The extract from ovaries formed a different retarded band. The results, taken together, indicate that production of transgenic Xenopus is very useful for the analysis of the promoter activity of genes in amphibians. The results also suggest that at least two proteins (one in the embryo and the other in the ovary of 2-month-old postmetamorphosing Xenopus) bind the 0.3 kb 5'-flanking region of the FTZ-F1alpha gene. These proteins may be involved in the regulation of FTZ-F1alpha gene expression in amphibians.

The Dmrt1 expression in sex-reversed gonads of amphibians

Gonadal differentiation in amphibians is sensitive to steroids. The phenotypic sex can be changed by hormonal treatments, but the molecular mechanism for gonadal differentiation is not known. Up to date, many genes involved in gonadal differentiation have been isolated in vertebrates. Dmrt1, a gene that contains the DM-domain (Doublesex/Mab-3 DNA-binding motif), is considered to be one of the essential genes involved in the testicular differentiation cascade in mammals, birds, reptiles, and fish. However, this gene has not been isolated in amphibians yet. To elucidate its role(s) for gonadal differentiation in vertebrates, a molecular cloning of Dmrt1 in amphibians is urgent. In this study, we have successfully isolated a Dmrt1 homolog from the frog Rana rugosa testes cDNA library and examined its expression during gonadal differentiation and in sex-reversed gonads. The Dmrt1 mRNA was exclusively detected in testis among adult tissues by the RT-PCR analysis. The Dmrt1 was first expressed in the differentiating testis at stage XXV in which spermatogonia are only germ cells, and became stronger at later stages. Moreover, the Dmrt1 transcript was not detected during ovarian differentiation. However, this gene was clearly expressed in XX sex-reversed gonads caused by injection of testosterone into all-female tadpoles that have well-differentiated ovaries. Taken together, the results suggest that Dmrt1 is closely implicated in testicular, but not ovarian differentiation in amphibians.

Expression of Dax-1 during gonadal development of the frog

Dax-1, a member of the nuclear hormone receptor superfamily of transcription factors, is known to be involved in gonadal development in mammals. To date, Dax-1 has only been isolated in reptiles, birds and mammals. The expression of Dax-1 is down-regulated in the developing testis, but persists in the ovary of mice (Swain et al., Nat. Genet. 12 (1996) 404) and chicken (Smith et al., J. Mol. Endocrinol. 24 (2000) 23). Curiously, there is no sex difference in the expression patterns of Dax-1 in the American alligator (Western et al., Gene 241 (2000) 223). To understand its role(s) in gonadal development in vertebrates, molecular cloning of Dax-1 in amphibians is required. In this study, we cloned an amphibian Dax-1 homologue of the frog Rana rugosa and examined its expression profile during gonadal development. Cloned Dax-1 cDNA encoded a protein of 287 amino acids. Unlike mammalians that possess the three and one half repeat elements representing the putative DNA binding domain in the predicted sequence of Dax-1 protein, the frog had a single poorly conserved copy of the repeat unit. By RT-PCR analysis, the Dax-1 mRNA was detected in the liver and pancreas, but not in the testis and ovary of adult frogs. However, Dax-1 expression was seen first in the embryo at stage 12 and became stronger in tadpoles until stage X. The Dax-1 was transcribed in the testis stronger than in the ovary of frogs at stage XXV (just after completion of metamorphosis). In the gonad of frogs 2 months after metamorphosis (at this stage postmeiotic cells can be seen in the seminiferous tubules), the Dax-1 was expressed only in males. In addition, the Dax-1 transcription declined gradually as ovarian development proceeded, but its expression was down-regulated and then up-regulated rapidly when female-to-male sex reversal was caused by administration of testosterone into female tadpoles. Taken together, the results suggest that the Dax-1 may be closely involved in testicular development of amphibians.

Expression of FTZ-F1alpha in frog testicular cells

Fushi tarazu transcription factor-1 (FTZ-F1), a member of a nuclear hormone receptor superfamily, is a transcriptional regulator for fushi tarazu gene expression in Drosophila (Ueda et al., '90). We have cloned a homologue (rrFTZ-F1alpha) of the FTZ-F1 gene of the frog Rana rugosa. The gene, in frogs, has been shown to have high expression level in the testis (Nakajima et al., 2000). In this study, the RT-PCR analysis showed that the FTZ-F1alpha mRNA level in adult frogs did not change throughout the year, even during hibernation. However, when immunohistological studies using the anti-rrFTZ-F1alpha antibody were employed to examine which testicular cells expressed this gene, Sertoli cells were found to produce rrFTZ-F1alpha in the two seasons: the breeding season (from March through May) and the pre-hibernating season (from October through November). Interstitial cells, however, did it in only the breeding season (from April through May). Taken together, the results suggest that the rrFTZ-F1alpha expression is regulated at the post-transcriptional step, and that the rrFTZ-F1alpha may play an important role(s) in the seasonal activities of Sertoli and interstitial cells in the frog testis. J. Exp. Zool. 290:182-189, 2001.

The mouse fetoprotein transcription factor (FTF) gene promoter is regulated by three GATA elements with tandem E box and Nkx motifs, and FTF in turn activates the Hnf3beta, Hnf4alpha, and Hnf1alpha gene promoters

Fetoprotein transcription factor (FTF) is an orphan nuclear receptor that activates the alpha(1)-fetoprotein gene during early liver developmental growth. Here we sought to define better the position of FTF in transcriptional cascades leading to hepatic differentiation. The mouse FTF gene was isolated and assigned to chromosome 1 band E4 (one mFTF pseudogene was also found). Exon/intron mapping shows an mFTF gene structure similar to that of its close homologue SF1, with two more N-terminal exons in the mFTF gene; exon mapping also delimits several FTF mRNA 5'- and 3'-splice variants. The mFTF transcription initiation site was located in adult liver at 238 nucleotides from the first translation initiator codon, with six canonical GATA, E box, and Nkx motifs clustered between -50/-140 base pairs (bp) from the cap site; DNA/protein binding assays also pinpointed an HNF4-binding element at +36 bp and an FTF-binding element at -257 bp. Transfection assays and point mutations showed that the mFTF promoter is activated by GATA, HNF4alpha, FTF, Nkx, and basic helix-loop-helix factors, with marked cooperativity between GATA and HNF4alpha. A tandem GATA/E box activatory motif in the proximal mFTF promoter is strikingly similar to a composite motif coactivated by differentiation inducers in the hematopoietic lineage; a tandem GATA-Nkx motif in the distal mFTF promoter is also similar to a composite motif transducing differentiation signals from transforming growth factor-beta-like receptors in the cardiogenic lineage. Three genes encoding transcription factors critical to early hepatic differentiation, Hnf3beta, Hnf4alpha, and Hnf1alpha, each contain dual FTF-binding elements in their proximal promoters, and all three promoters are activated by FTF in transfection assays. Direct DNA binding action and cooperativity was demonstrated between FTF and HNF3beta on the Hnf3beta promoter and between FTF and HNF4alpha on the Hnf1alpha promoter. These combined results suggest that FTF is an early intermediary between endodermal specification signals and downstream genes that establish and amplify the hepatic phenotype.

Developmental expression patterns of FTZ-F1 homologues in zebrafish (Danio rerio)

The fushi tarazu factor 1 (FTZ-F1) gene family constitutes a subgroup of orphan nuclear receptors which can be divided into two groups (LRH/FTF- and SF-1/Ad4BP-like) based on sequence homology, function, and tissue distribution. Analysis of zebrafish FTZ-F1 homologues (zFF1 and ff1b) during embryogenesis indicated distinct expression patterns for both genes. Besides the previously observed expression in pituitary/hypothalamus and mandibular arch, zFF1 transcripts were also detected in domains corresponding to the pronephric duct, somites, liver, and hindbrain. Additionally, ff1b transcripts were detected at other developmental stages than earlier documented. Comparative sequence analysis showed that zFF1 exhibited higher sequence similarity to the LRH/FTF group than the SF-1/Ad4BP group, whereas ff1b was indistinguishable between the groups. These observations, coupled with obtained expression patterns, indicate that zebrafish FTZ-F1 homologues exhibit characteristics that are indicative of both LRH/FTF- and SF-1/Ad4BP-like genes.