Androgen-binding Protein Gene Research Articles

Reduced testosterone and Ddx3y expression caused by long-term exposure to arsenic and its effect on spermatogenesis in mice

Arsenic (As) has been recognized as a cause of male reproductive toxicity. However, effects of long-term arsenic exposure (puberty–adult) on spermatogenesis, testosterone synthesis, and the expression of androgen binding protein (ABP) and Ddx3y remain unclear. The objective of this investigation was to explore these effects and the underlying mechanisms. Male mice were treated with 5 and 50 ppm arsenic for 6 months via drinking water. The results showed that arsenic reduced sperm count and sperm motility and enhanced the abnormal sperm percentage. The decrease in the number of spermatogenic cells and sperm in seminiferous tubules and the decline in the Johnsen score were observed in both arsenic-treated groups, suggesting spermatogenesis disorders. Moreover, arsenic diminished serum testosterone, along with the reduced expression of luteinizing hormone receptor (LHR), steroidogenic acute regulatory protein (StAR) and 17-β-hydroxysteroid dehydrogenase (17β-HSD) genes. Arsenic also down-regulated mRNA levels of ABP and Ddx3y in a dose-dependent manner. Meanwhile, the protein levels of StAR, 17β-HSD and Ddx3y were significantly reduced in arsenic-treated groups. Taken together, these results suggest that the reduced testosterone through inhibition of the expression of multiple genes responsible for the biosynthesis, the damaged androgen homeostasis partially via lessening the expression levels of the ABP gene and the down-regulated expression of Ddx3y, may contribute to spermatogenesis disorders in mice exposed to arsenic.

A candidate subspecies discrimination system involving a vomeronasal receptor gene with different alleles fixed in M. m. domesticus and M. m. musculus

Assortative mating, a potentially efficient prezygotic reproductive barrier, may prevent loss of genetic potential by avoiding the production of unfit hybrids (i.e., because of hybrid infertility or hybrid breakdown) that occur at regions of secondary contact between incipient species. In the case of the mouse hybrid zone, where two subspecies of Mus musculus (M. m. domesticus and M. m. musculus) meet and exchange genes to a limited extent, assortative mating requires a means of subspecies recognition. We based the work reported here on the hypothesis that, if there is a pheromone sufficiently diverged between M. m. domesticus and M. m. musculus to mediate subspecies recognition, then that process must also require a specific receptor(s), also sufficiently diverged between the subspecies, to receive the signal and elicit an assortative mating response. We studied the mouse V1R genes, which encode a large family of receptors in the vomeronasal organ (VNO), by screening Perlegen SNP data and identified one, Vmn1r67, with 24 fixed SNP differences most of which (15/24) are nonsynonymous nucleotide substitutions between M. m. domesticus and M. m. musculus. We observed substantial linkage disequilibrium (LD) between Vmn1r67 and Abpa27, a mouse salivary androgen-binding protein gene that encodes a proteinaceous pheromone (ABP) capable of mediating assortative mating, perhaps in conjunction with its bound small lipophilic ligand. The LD we observed is likely a case of association rather than residual physical linkage from a very recent selective sweep, because an intervening gene, Vmn1r71, shows significant intra(sub)specific polymorphism but no inter(sub)specific divergence in its nucleotide sequence. We discuss alternative explanations of these observations, for example that Abpa27 and Vmn1r67 are coevolving as signal and receptor to reinforce subspecies hybridization barriers or that the unusually divergent Vmn1r67 allele was not a product of fast positive selection, but was derived from an introgressed allele, possibly from Mus spretus.

A Candidate Subspecies Discrimination System Involving a Vomeronasal Receptor Gene with Different Alleles Fixed in M. m. domesticus and M. m. musculus

Assortative mating, a potentially efficient prezygotic reproductive barrier, may prevent loss of genetic potential by avoiding the production of unfit hybrids (i.e., because of hybrid infertility or hybrid breakdown) that occur at regions of secondary contact between incipient species. In the case of the mouse hybrid zone, where two subspecies of Mus musculus (M. m. domesticus and M. m. musculus) meet and exchange genes to a limited extent, assortative mating requires a means of subspecies recognition. We based the work reported here on the hypothesis that, if there is a pheromone sufficiently diverged between M. m. domesticus and M. m. musculus to mediate subspecies recognition, then that process must also require a specific receptor(s), also sufficiently diverged between the subspecies, to receive the signal and elicit an assortative mating response. We studied the mouse V1R genes, which encode a large family of receptors in the vomeronasal organ (VNO), by screening Perlegen SNP data and identified one, Vmn1r67, with 24 fixed SNP differences most of which (15/24) are nonsynonymous nucleotide substitutions between M. m. domesticus and M. m. musculus. We observed substantial linkage disequilibrium (LD) between Vmn1r67 and Abpa27, a mouse salivary androgen-binding protein gene that encodes a proteinaceous pheromone (ABP) capable of mediating assortative mating, perhaps in conjunction with its bound small lipophilic ligand. The LD we observed is likely a case of association rather than residual physical linkage from a very recent selective sweep, because an intervening gene, Vmn1r71, shows significant intra(sub)specific polymorphism but no inter(sub)specific divergence in its nucleotide sequence. We discuss alternative explanations of these observations, for example that Abpa27 and Vmn1r67 are coevolving as signal and receptor to reinforce subspecies hybridization barriers or that the unusually divergent Vmn1r67 allele was not a product of fast positive selection, but was derived from an introgressed allele, possibly from Mus spretus.

Effect of thyroid hormone on the development and gene expression of hormone receptors in rat testes in vivo

Thyroid hormone is known to play a pivotal role in the regulation of prepuberal rat testes development and function with specific influence on the differentiation of Sertoli cells, the only cell type that expresses thyroid hormone receptors in testes. To explore in vivo effects of thyroid hormone on testes development and the regulation of testicular gene expression, the hyper- and hypothyroid rat models were established by T3 injection to pups (ip 100 microg/kg bw) and by oral administration of 6-N-propyl-2-thiouracil (PTU) to the lactating mother from days 1 to 21 post-delivery. Half of the rats from each group were sacrificed at 21 days of age, and the other half were allowed to recover with discontinued treatments from day 22 to day 50. At 21 days of age, a significantly elevated serum T3 level was observed in hyperthyroid rats (179.5 ng/dl) vs controls (97.5 ng/dl), and in hypothyroid rats a significantly lower level of T3 was detected (26.1 ng/dl). However, serum T4 concentration was significantly lower in both hyper- (0.105 microg/dl) and hypothyroid (0.058 microg/dl) rats compared to the controls (2.48 microg/dl). In recovered rats in which the serum T3 and T4 were restored to normal, the serum T levels remained remarkably lower in both hyper- and hypothyroid rats. The significantly decreased body and testes weights observed in both hyper- and hypothyroid rats at 21 days of age were not restored by the time they were 50 days old. Histological analyses of testes of 21-day-old hypothyroid rats revealed smaller-sized seminiferous tubules, incomplete lumen formation and delayed germ cell differentiation and in hyperthyroid rats an increased number of early stage spermatocytes was found. Testicular mRNA levels of follicle-stimulating hormone receptor (FSH-R), luteinizing hormone receptor (LH-R) and androgen binding protein (ABP) were studied by Northern blot hybridization. At 21 days of age data showed that FSH-R mRNA levels were significantly higher in both hyper- and hypothyroid rat testes compared to controls, but no differences were detected in recovered 50-day-old rats. Significantly decreased ABP mRNA levels were detected only in hypothyroid rat testes compared to those in both the hyperthyroid and control groups at 21 days of age, but no significant change was observed in recovered 50-day-old rats. To further evaluate the effect of thyroid hormone on the Leydig cell function, the 2.3/2.6 kb specific LH-R hybridization bands were detected with rat LH-R cRNA probe. Significant suppression of LH-R mRNA levels was only observed in the hypothyroid rat testes at 50 days of age. The testicular thyroid hormone receptors (TRs) and the regulation of TR by thyroid hormone were investigated using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. Both TRalpha and TRbeta mRNAs were identified in the testes from 21- and/or 50-day-old rats. TRalpha mRNA levels were significantly increased in hypothyroid rat testes and were suppressed in hyperthyroid rats at 21 days of age and no changes of TRalpha mRNA were found in recovered animals. Our in vivo data strongly suggest that the thyroid hormone directly affects the development of prepuberal testes and the regulation of FSH-R and ABP gene expression in Sertoli cells, as well as the LH-R mRNA levels in Leydig cells, which may lead to further modulating the effect of gonadotropins on testes function.

An activated human follicle-stimulating hormone (FSH) receptor stimulates FSH-like activity in gonadotropin-deficient transgenic mice.

FSH mediates its testicular actions via a specific Sertoli cell G protein-coupled receptor. We created a novel transgenic model to investigate a mutant human FSH receptor (FSHR(+)) containing a single amino acid substitution (Asp567Gly) equivalent to activating mutations in related glycoprotein hormone receptors. To examine the ligand-independent gonadal actions of FSHR(+), the rat androgen-binding protein gene promoter was used to direct FSHR(+) transgene expression to Sertoli cells of gonadotropin-deficient hypogonadal (hpg) mice. Both normal and hpg mouse testes expressed FSHR(+) mRNA. Testis weights of transgenic FSHR(+) hpg mice were increased approximately 2-fold relative to hpg controls (P < 0.02) and contained mature Sertoli cells and postmeiotic germ cells absent in controls, revealing FSHR(+)-initiated autonomous FSH-like testicular activity. Isolated transgenic Sertoli cells had significantly higher basal ( approximately 2-fold) and FSH-stimulated ( approximately 50%) cAMP levels compared with controls, demonstrating constitutive signaling and cell-surface expression of FSHR(+), respectively. Transgenic FSHR(+) also elevated testosterone production in hpg testes, in the absence of circulating LH (or FSH), and it was not expressed functionally on steroidogenic cells, suggesting a paracrine effect mediated by Sertoli cells. The FSHR(+) response was additive with a maximal testosterone dose on hpg testicular development, demonstrating FSHR(+) activity independent of androgen-specific actions. The FSHR(+) response was male specific as ovarian expression of FSHR(+) had no effect on hpg ovary size. These findings reveal transgenic FSHR(+) stimulated a constitutive FSH-like Sertoli cell response in gonadotropin-deficient testes, and pathways that induced LH-independent testicular steroidogenesis. This novel transgenic paradigm provides a unique approach to investigate the in vivo actions of mutated activating gonadotropin receptors.

Sertoli cell-specific expression of rat androgen-binding protein in transgenic mice: effects on somatic cell lineages

The Sertoli cells of many species produce an androgen binding protein (ABP) which carries testicular androgens to the epididymis and is thought to play a role in sperm maturation. In the present report we analyzed the morphological modifications present in Leydig, Sertoli, and peritubular cells of the testis of young adult male mice transgenic for ABP gene, which overproduce ABP in testis. By in situ hybridization we demonstrated that ABP is specifically produced by Sertoli cells. Using light and electron microscopy, we detected scattered alterations of the seminiferous tubule cells which include cell degeneration and vacuolization. Leydig and Sertoli cells present morphological signs of hyperfunctioning compensatory mechanisms which include increased amounts of lipid droplets probably due to the existence of a stimulated steroid synthesis that in turn could be a consequence of the decreased unbound testosterone and/or a direct paracrine effect of ABP. Peritubular cells also present numerous signs of hyperstimulation.

DNA sequences and their binding proteins required for Sertoli cell-specific transcription of the rat androgen-binding protein gene.

The rat androgen-binding protein (ABP) gene is transcriptionally regulated from two promoters: the P1 promoter regulates expression of transcripts starting at exon 1, whereas P(A) regulates transcripts containing exon A. The P1 promoter directs cell-specific gene regulation of ABP secreted by Sertoli cells. In this study, the Sertoli cell-regulatory sequences of P1 were further examined using a luciferase reporter system with three cell lines, including a Sertoli cell line (MSC-1) that expresses the ABP gene. Deletion mapping experiments determined that the sequences required for full activity in MSC-1 cells were included within 619 bp of the start site and identified several regions that demonstrated increased luciferase activity: the -583 bp to -564 bp, -503 bp to -484 bp, and -114 bp to -65 regions. The activities contributed by each region were much higher (up to 120-fold) in MSC-1 cells than in MA10 Leydig or NIH3T3 fibroblast cells. Nuclear-binding proteins and their binding sequences were identified using several molecular biology techniques. Complexes formed by nuclear proteins of MSC-1, MA10, and NIH3T3 cells, which bind specifically to the -114 to -65-bp region, were identified using gel retardation assays. Furthermore, the inverted repeat sequence in this region, 5'-AGGGTCAGTGTCCCT-3' was identified by deoxyribonuclease (DNase) I footprinting. The regulatory element contained within the -503 to -484-bp region was identified by scanning mutagenesis, but no protein was found that bound to this sequence by gel retardation or DNase I protection assays. This element is characterized by the core sequence, 5'-GGAGGC-3'. The third regulatory region (residues -583 to -564) bound a protein complex that retarded mobility of the free DNA probe in a gel shift assay. Using several techniques, the binding sequence was identified as 5'-TTCATAGTATCCATTAAAC-3'. In summary, these data have identified several transcriptional regulatory sequences and their binding proteins, which appear to play a role in the Sertoli cell-specific expression of the ABP gene.

DNA Sequences and Their Binding Proteins Required for Sertoli Cell-Specific Transcription of the Rat Androgen-Binding Protein Gene

DNA Sequences and Their Binding Proteins Required for Sertoli Cell-Specific Transcription of the Rat Androgen-Binding Protein Gene

Exon skipping and circular RNA formation in transcripts of the human cytochrome P-450 2C18 gene in epidermis and of the rat androgen binding protein gene in testis.

The cytochrome P-450 2C18 gene was found by reverse transcription-PCR to represent the most abundantly expressed gene of the P-450 2C subfamily in human epidermis. However, in addition to the canonical mRNA of nine exons, transcripts that have skipped exon 4 or 5, exons 4, 5, and 6, or exons 4, 5, 6, and 7 were also identified in this tissue. Remarkably, circular RNA transcripts synthesized by the joining of the donor and acceptor splice sites of the same exon were detected in human epidermis for exons 4 and 5. Moreover, molecules composed of exons 4, 5, and 6 with the donor splice site of exon 6 joined to the acceptor splice site of exon 4 or composed of exons 4, 5, 6, and 7 with the donor splice site of exon 7 joined to the acceptor splice site of exon 4 were also found to be present in this tissue. In rat testis, a similar analysis allowed the detection of a circular RNA molecule composed of exons 6 and 7 of the androgen binding protein (ABP) gene, with the donor splice site of exon 7 joined to the acceptor splice site of exon 6, and of an ABP mRNA which had skipped exons 6 and 7. These results apparently substantiate the hypothesis that alternative pre-mRNA splicing has the potential to generate not only mRNAs that lack one or more exons but also circular RNA molecules that are composed of the exons that are skipped. However, additional 2C18 circular species containing various combinations of exons were also detected in human epidermis, and an exon 6-skipped ABP mRNA molecule was identified in rat testis. This observation is interpreted as indicative that at low frequency, numerous circular RNA formation and exon skipping events may occur, allowing the joining of a variety of different combinations of exons. Moreover, the relative stability of these molecules is apparently the key factor that determines the relative ease of their detection.

Expression and distribution of androgen-binding protein/sex hormone-binding globulin in the female rodent reproductive system.

Androgen-binding protein (ABP)/sex hormone-binding globulin gene expression has been described in the rat testicular Sertoli cell and brain. The extracellular protein is thought to regulate the bioavailability of sex steroids, but may have a more complex function as a hormone or growth factor. Transgenic mice were developed with a 5.5-kilobase (kb) rat DNA fragment containing the ABP gene with all 8 exon sequences and 1.5 kb upstream of the transcription start site. Expression of the gene was observed in the testis and brain, but not in other examined tissues of the transgenic mice. In this paper we describe ABP gene expression in ovaries of transgenic mice that contain the rat gene; a lower level of ABP mRNA was also detected in the transgenic uterus. Northern blot analysis also detected ABP mRNA in rat ovary. The hybridizing species in the rat and transgenic mouse ovaries and uteri were the size of testicular ABP mRNA (1.7 kb). Except in the transgenic mouse brain, there was no detectable hybridizing RNA in the other transgenic tissues examined. The plasma, ovary, and uterus of the transgenic mice all contained elevated ABP (dihydrotestosterone [DHT]-binding) activities as compared to those of wild-type littermates; other wild-type and transgenic tissues were negative for DHT binding. Immunohistochemistry revealed increased immunoreactivity in the transgenic oviduct and uterus, but not the ovary. In the oviduct, the intense immunoreactivity was associated with the epithelium, whereas in the uterus it was primarily associated with the luminal epithelium and glands. Phenotypic abnormalities of the homozygous transgenic mice included reduced fecundity resulting in small litters. We conclude that ABP may function in the female reproductive system to increase the local concentrations of sex steroids or to sequester them in key target organs. Studies in the female will aid in elucidating the functions of ABP in male and female reproduction.

Glucocorticoid Regulation of Androgen Binding Protein Expression in Primary Sertoli Cell Cultures from Rats

Glucocorticoids are known to inhibit testicular function, and its receptor is also localized in the Sertoli cells. To evaluate possible role of glucocorticoid in Sertoli cells, the effects of dexamethasone on the expression of androgen binding protein (ABP) have been investigated in primary Sertoli cell cultures. Dexamethasone increased ABP mRNA levels, with maximal stimulation reached at 36 hr. The induction of ABP mRNA was dependent on the low concentration (10−8and 10−7M) of dexamethasone but gradually reduced in the cells treated with high concentration (10−6and 10−5M). Dexamethasone-induced ABP mRNA level was no change in the cells after addition of cycloheximide but almost reduced by actinomycin-D pretreatment. Steady-state levels of ABP mRNA gradually increased in the Sertoli cells prepared from 14- and 21-days of age corresponding to rat puberty, and ABP mRNA was induced by dexamethasone. These results suggest that ABP gene is transcriptionally regulated by dexamethasone in primary Sertoli cell cultures.

Effects of photoperiod on testicular inhibin-α and androgen binding protein mRNA expression during postnatal development in siberian hamsters, [formula omitted

The effects of short photoperiod (SPP) on testicular inhibin-α and androgen binding protein (ABP) mRNA expression were investigated in Siberian hamsters during postnatal development. Hamsters were raised in either long photoperiod (LPP; 16L:8D) or in a SPP (6L:18D). Hamsters were sacrificed at the following developmental ages: preweaning (18–20 days), immature (28–30 days), pubertal (38–40 days), postpubertal (48–50 days) and adult (60–62 days; n = 7–12 animals per group). Body and testicular weights were determined and plasma FSH levels were measured by validated RIA. As expected, testicular weight and circulating FSH levels were significantly lower in hamsters raised in SPP than in LPP animals. Photoperiod had no significant effect on body weight except during postpubertal age. The northern analyses of inhibin-α and ABP expression in the testes revealed that the corresponding relative mRNA levels were higher in animals exposed to SPP than in animals from LPP. These findings suggest that the testes of hamsters exposed to a SPP can synthesize inhibin-α and ABP and we speculate that the release of these proteins may be regulated by photoperiod and the role of FSH in the control of inhibin-α and ABP gene expression in male Siberian hamsters may be minimal.

Androgen binding protein is tissue-specifically expressed and biologically active in transgenic mice

In view of the inconclusive data concerning the role of androgen-binding protein (ABP) in male reproductive physiology, we thought it would be pertinent to make several transgenic mouse lines overexpressing the rat ABP gene to unravel its role in Sertoli cell and epididymal homeostasis. Heterozygote transgenic mouse lines carrying the 5.5 kb ABP rat genomic DNA were produced by pronuclear microinjection. Northern blot analysis showed overexpression of rat ABP (rABP) mRNA in the testis of transgenic mice compared to rat testis control. rABP was appropriately expressed in Sertoli cells as demonstrated by in situ hybridization analysis. Sertoli cell number is increased in the seminiferous tubules of mice overexpressing rABP compared to non-transgenic littermates and scattered Sertoli cells present vacuolated-like cytoplasms, PAS and osmium negative. Compared to the wild type, the transgenic mice exhibited reduced fertility and focal damage in seminiferous epithelium characterized by morphological features compatible with programmed cell death.

Tissue-specific expression of the rat androgen-binding protein/sex hormone-binding globulin gene in transgenic mice

The testicular Sertoli cell produces an extracellular androgen-binding protein (ABP) that binds testosterone and dihydrotestosterone with high affinity. The ABP gene also encodes plasma sex hormone-binding globulin (SHBG), which is produced by the liver of most species. Unlike the human, adult rats and mice do not express SHBG. A 5.5-kb rat genomic DNA fragment was found to contain the entire coding region of ABP and 1.5 kb upstream of the transcription start site. To aid in identification of the promoter and enhancer regions of the ABP/SHBG gene, we developed transgenic mice that express the rat gene. The 5.5-kb DNA was microinjected into the pronuclei of fertilized mice ova, which were transferred to the reproductive tract of pseudopregnant females. Three of the offspring were identified as carriers of the rat gene by Southern hybridization and these founders were bred with normal mice to establish heterozygous transgenic lines. Northern blot analysis, RNA-PCR and sequencing of the PCR products from the adult transgenic mice revealed extremely high levels of the rat ABP mRNA in the testis, but no detectable rat ABP mRNA in liver, kidney or brain. Primer extension experiments showed that the correct transcript ion start site is utilized in the transgenes. These data demonstrate that the 5.5-kb genomic DNA fragment contains an element(s) capable of directing ABP gene expression in the testis. This enhancer should prove useful for the targeting of specific gene products to the mature Sertoli cell in transgenic animals.

Demonstration of Androgen-Binding Protein Gene Expression in Primary Neuronal and Astrocyte Cultures

Testicular androgen-binding protein (ABP) and liver (plasma) sex hormone-binding globulin (SHBG) are extracellular carrier proteins. They are encoded by the same gene and have the identical primary amino acid sequence. The ABP/SHBG gene is also expressed in rat brain; immunoreactive neurons are located throughout the male and female brain and immunoreactive fibers are present in the ventral hypothalamus. ABP/SHBG RNA transcripts are synthesized from two promoters, P 1 and P A. P 1 regulates synthesis of the mRNA that encodes secreted ABP, whereas, a P A mRNA encodes a nonsecreted ABP-like protein without steroid binding properties. P A and P 1 transcripts are expressed in the brain. In this study, we demonstrated by Northern hybridization analysis that primary neuronal and astrocyte cultures express ABP mRNA. PCR analysis of ABP cDNA revealed that astroglia express transcripts originating from promoters P 1 and P A, whereas, neuronal cDNAs contain primarily PA transcripts. These ABP cDNA-hybridizing products represent mRNAs that encode secreted ABP and the nonsecreted ABP-like protein. Furthermore, it was shown by immunohistochemistry that cultured astrocytes contain immunoreactive ABP. Western blots of astrocyte proteins yielded immunoreactive ABP migrating as 38,000-, 34,000-, and 24,060- M r proteins. The sizes of these proteins do not correspond to the protein-encoding properties of P 1 or P A ABP mRNA or any known alternatively processed ABP mRNAs, suggesting that they are derived by proteolytic processing of ABP or the ABP-like protein (46,000 Da). The function of the ABP gene products in brain is not obvious. We speculate that ABP may act as a carrier protein for an unknown ligand in axonal transport.

Alternative processing of androgen-binding protein RNA transcripts in fetal rat liver. Identification of a transcript formed by trans splicing.

Androgens and their nuclear receptor regulate genes necessary for development of the male phenotype, a process that is thought to be modulated by extracellular androgen carrier proteins. Two of these carrier proteins, testicular androgen-binding protein (ABP) and plasma sex hormone-binding globulin (SHBG), are encoded by the same gene, but differ in glycosylation and possibly amino acid sequence. To investigate ABP-SHBG gene expression in fetal rat liver, we analyzed RNA transcripts and expressed protein. These studies demonstrated a transient expression of ABP in hepatocytes during the time of testosterone-dependent differentiation of the Wolffian duct. Analysis of cDNA clones derived from fetal rat liver cDNA libraries identified two cDNAs encoded by the ABP-SHBG gene that represented alternatively spliced RNAs. One cDNA had an alternate exon 1, suggesting the function of another promoter in fetal liver. This cDNA also lacked testicular exon 6 DNA, an alteration that implicates the encoded protein in regulatory functions. The other cDNA represented a fused transcript of the ABP-SHBG gene (exons 1-5) and the histidine decarboxylase (HDC) gene, encoding a Mr 98,000 precursor protein. The two domains were joined at splice junctions of the ABP-SHBG and HDC genes, which were localized to rat chromosomes 10 and 3, respectively. Our results indicate that the joining of the two domains was by a trans (donor and acceptor)-splicing mechanism. Data from Northern hybridization experiments suggest the fusion transcript is present in fetal liver RNA. Polymerase chain reaction experiments with fetal liver cDNA further support the existence of an ABP-HDC fusion transcript, as well as the other alternate mRNA. Moreover, a Mr 93,000 immunoreactive protein was transiently expressed in fetal liver during the time of ABP and HDC gene expression. Expression of the fusion cDNA in COS cells yielded HDC activity and the predicted size protein (Mr = 93,000) on Western immunoblots.

The Androgen-Binding Protein Gene Is Expressed in Male and Female Rat Brain*

Extracellular androgen-binding proteins (ABP) are thought to modulate the regulatory functions of androgens and the trans-acting nuclear androgen receptor. Testicular ABP and plasma sex hormone-binding globulin (SHBG), which is produced in liver, are encoded by the same gene. We have now found that the ABP-SHBG gene is also expressed in male and female rat brain. Immunoreactive ABP was found to be present in neuronal cell bodies throughout the brain as well as in fibers of the hypothalamic median eminence. The highest concentrations of immunoreactive cell bodies were located in the supraoptic and paraventricular nuclei. Likewise, ABP mRNA was present in all brain regions examined. Analysis of cDNA clones representing brain ABP mRNAs revealed amino acid sequence differences in brain and testicular ABPs. The protein encoded by an alternatively processed RNA has sequence characteristics suggesting that the protein could act as a competitior of ABP binding to cell surface receptors. These data and gene-sequencing experiments indicate that a specific ABP gene promoter is used for transcription initiation in brain. ABP may function in brain as an androgen carrier protein; however, in view of the widespread presence of ABP and ABP mRNA in brain, the protein may have a much broader, yet unknown, function.

The androgen-binding protein gene is expressed in CD1 mouse testis

Androgen-binding protein (ABP) is a testicular Sertoli cell secretory protein that acts as a carrier of androgen in the male reproductive tract. ABP has been characterized from a wide range of animal species, including man, rabbit and rat. However, it has been widely accepted that mice do not produce testicular ABP. We have used immunological and molecular biological techniques to demonstrate that the ABP gene is expressed in the CD1 mouse. Steroid-binding, radioimmunoassay and immunocytochemical studies demonstrated that ABP is present in mouse testis and epididymis, but at 1 50 to 1 25 the level of rat epididymis. A 1.7 kilobase mRNA, homologous with rat ABP cDNA, was identified in mouse testis and Sertoli cells by Northern blot hybridization, but at a much lower level than in the rat. An ABP cDNA was isolated from a mouse testis cDNA library and encoded a protein (403 residues) with 89% of the amino acid residues identical to rat ABP, including a signal peptide. Our results indicate that ABP is expressed in the mouse and past failures to detect androgen-binding activity were due to the low level of ABP protein.