Synthesis of specific brain proteins is influenced by testosterone at mRNA level in the neonatal rat

MeCP2 regulates GFAP expression within the developing brain

Mutations in MECP2 cause Rett syndrome (RTT), an X-linked neurodevelopmental disorder that primarily affects females. Individuals with RTT have increased glial fibrillary acidic protein (GFAP) expression in the brain. GFAP is an intermediate filament protein that is expressed predominately within astrocytes in the CNS. MeCP2 binds to methylated regions of the GFAP promoter region and suppresses GFAP expression in vitro. Therefore, we wanted to determine if transiently reducing MeCP2 expression would increase GFAP expression in the developing rat brain. Male and female rats received infusions of either MeCP2 or control siRNA targeting the amygdala during the first 3 days of postnatal life. Brains were collected after 6h or 2 weeks following the last infusion. MeCP2 siRNA increased GFAP mRNA and protein within the female, but not the male, amygdala on postnatal day (PN) 2. Two weeks following the infusion, levels returned to normal. MeCP2 siRNA targeting the hypothalamus also increases GFAP mRNA within the female hypothalamus on PN2, suggesting that the regulation is not brain region-specific. It appears that MeCP2 does not regulate all astrocyte markers in the developing female brain, but specifically regulates GFAP expression, as levels of S100β and vimentin were not altered in the female amygdala at either time point. These data contribute to the idea that the role of MeCP2 differs in the developing male versus female brain. Further elucidating the regulation and function of GFAP can contribute to our understanding of MeCP2 function and perhaps RTT etiology.

Sex differences in epigenetic regulation of the estrogen receptor-alpha promoter within the developing preoptic area

Sex differences in the brain are largely organized by a testicular hormone surge that occurs in males shortly after birth. Although this hormone surge is transient, sex differences in brain and behavior are lasting. Here we describe a sex difference in DNA methylation of the estrogen receptor-alpha (ERalpha) promoter region within the developing rat preoptic area, with males exhibiting more DNA methylation within the ERalpha promoter than females. More importantly, we report that simulating maternal grooming, a form of maternal interaction that is sexually dimorphic with males experiencing more than females during the neonatal period, effectively masculinizes female ERalpha promoter methylation and gene expression. This suggests natural variations in maternal care that are directed differentially at males vs. females can influence sex differences in the brain by creating sexually dimorphic DNA methylation patterns. We also find that the early estradiol exposure may contribute to sex differences in DNA methylation patterns. This suggests that early social interaction and estradiol exposure may converge at the genome to organize lasting sex differences in the brain via epigenetic differentiation.

Mecp2 organizes juvenile social behavior in a sex-specific manner

Methyl-CpG-binding protein 2 (MeCP2) binds methylated DNA and recruits corepressor proteins to modify chromatin and alter gene transcription. Mutations of the MECP2 gene can cause Rett syndrome, whereas subtle reductions of MeCP2 expression may be associated with male-dominated social and neurodevelopmental disorders. We report that transiently decreased amygdala Mecp2 expression during a sensitive period of brain sexual differentiation disrupts the organization of sex differences in juvenile social play behavior. Interestingly, neonatal treatment with Mecp2 small interfering RNA within the developing amygdala reduced juvenile social play behavior in males but not females. Reduced Mecp2 expression did not change juvenile sociability or anxiety-like behavior, suggesting that this disruption is associated with subtle behavioral modification. This suggests that Mecp2 may have an overlooked role in the organization of sexually dimorphic behaviors and that male juvenile behavior is particularly sensitive to Mecp2 disruption during this period of development.

Prenatal testosterone improves the spatial learning and memory by protein synthesis in different lobes of the brain in the male and female rat

The high density of the steroid hormone receptors in the structures of temporal lobe involved in learning and memory, such as the hippocampus, perirhinal cortex, entorhinal cortex and amigdaloid complex, shows that there must be a direct relationship between gonadal hormones and organizational effects of steroid hormones in those structures during development of the nervous system. The present study was undertaken in order to investigate the effect of testosterone administration during the third week of gestation on the spatial memory formation of the offspring rats and the level of soluble proteins in the temporal lobe and frontal lobe of brain, as evidence of important organizational effects of androgens during prenatal development in brain sexual dimorphism. Animals have received testosterone undecanoate on days 14, 15, 16 and 19, 20, 21 of gestation. Learning and memory tests were started 100 days after the testosterone treatment. At the end of the experiments, the temporal and frontal lobes of brain were removed for assessing the level of soluble proteins. Testosterone treatment significantly improved spontaneous alternations percentage of male offspring in Y-maze task comparative with female offspring and reference memory in radial 8 arm-maze task (decreasing in number of reference memory errors in both male and female offspring groups), suggesting effects of both short and long-term memory. Also, testosterone significantly increased the brain soluble protein level of treated female rats in 14–16 prenatal days compared with the control group as well as the brain soluble protein level of treated male rats. These results suggest that steroid hormones play an important role in the spatial learning and memory formation by means of protein synthesis in different lobes of the brain.

Sex differences in Fos protein expression in the neonatal rat brain

Sex differences in the brain and behaviour are mostly a result of transient increases in testosterone during the perinatal period. Testosterone influences brain development primarily through aromatization to oestradiol and subsequent binding to oestrogen receptors. Although some studies report that steroid hormones regulate the expression of the inducible transcription factor, Fos, in developing brain, it is not known if there is a sex difference in Fos expression. Changes in Fos protein can be used as an indicator of neuronal/genomic activity. Thus, it provides a useful tool to identify brain regions responding directly or indirectly to steroid hormones. In a first experiment, we examined Fos protein expression in the developing male and female rat brain using western immunoblotting. Dissections were taken from male and female rat pups on the day of birth (postnatal day 0; PN 0), PN1, PN5, PN11 or PN20. Although there was no difference on PN 0, males expressed significantly greater levels of Fos protein on PN1, PN5 and PN20. In a second experiment, we localized the sex difference in Fos protein expression using immunocytochemistry. We found that males expressed significantly higher levels of Fos within a variety of brain regions. These data indicate a sex difference in Fos protein expression during brain development, suggesting a potential role for Fos in differentiating male from female rat brain.

Identification of a sex steroid-inducible gene in the neonatal rat hypothalamus

By the cDNA subtraction between cDNA preparations from androgenized and intact neonate rats hypothalami, granulin/ epithelin (grn) gene was identified as a gene enriched by androgenization. Strong grn mRNA signals were detected by in situ hybridization in the ventromedial nucleus (VMH) and the arcuate nucleus (ARC) of the hypothalamus of a 5-day-old male. The grn gene expression level in the hypothalamus was similar between males and females at birth. At 10 days of age, this level was maintained in males, but decreased to 1/4 in females. Thus, grn can be the gene of which expression in the VMH and ARC is sustained by endogenous androgen in male neonates.

Hormonally induced neuronal plasticity in the adult motoneurons

Sex steroids are known to play a crucial role in reproductive neuroendocrine functions in adulthood. A number of neurons in the neuroendocrine brain contain sex steroid receptors, and are thought to be a key element of functional neural circuits that are regulated by sex steroids. Motoneurons in the spinal nucleus of the bulbocavernosus in adult male rodents are one of the androgen-sensitive neural substrates. In the spinal nucleus of the bulbocavernosus, castration of adult male rats results in a significant decrease in the somatic size and dendritic length of the motoneurons, and in the number and size of chemical and electrical (gap junction) synapses onto these motoneurons. Androgen treatment of castrates reverses these changes. Furthermore, androgen has been reported to be involved in regulation of androgen receptor expression and gene expression of structural proteins such as beta-actin, beta-tubulin and gap junction channels in these motoneurons. The findings suggest that androgen induces morphological and molecular changes in the motoneurons that reflect their neural functions, and may provide evidence for the mechanisms of hormonally induced neuronal plasticity in the motoneurons in adulthood.

The canary androgen receptor mRNA is localized in the song control nuclei of the brain and is rapidly regulated by testosterone

Singing in canaries is an androgen-inducible behavior, under the control of an identified motor pathway, which includes several discrete "song nuclei" in the telencephalon. To determine whether the mRNA for the canary androgen receptor (cAR) is expressed in these song control nuclei, we synthesized probes from the recently cloned cAR cDNA and used in situ hybridization to examine spring male canary brain sections. Concentrations of cAR mRNA are detectable in several of the song control nuclei of the forebrain, including high vocal center (HVC), lateral magnocellular nucleus of the anterior neostriatum and robust nucleus of the archistriatum. In addition, we also show that testosterone treatment rapidly induces a significant reduction of cAR mRNA levels in nucleus HVC of females. Since the effects of androgen on singing behavior occur much more slowly, the behavioral effects are probably a secondary or independent result of androgen's primary and immediate action on target gene transcription.

Reciprocal regulation of estrogen and NGF receptors by their ligands in PC12 cells

Recent work has shown that estrogen receptor mRNA and protein co-localize with neurotrophin receptor systems in the developing basal forebrain. In the present study we examined the potential for reciprocal regulation of estrogen and neurotrophin receptor systems by their ligands in a prototypical neurotrophin target, the PC12 cell. Using in situ hybridization histochemistry, RT-PCR and a modified nuclear exchange assay, we found both estrogen receptor mRNA and estrogen binding in PC12 cells. Moreover, while estrogen binding was relatively low in naive PC12 cells, long-term exposure to NGF enhanced estrogen binding in these cells by sixfold. Furthermore, concurrent exposure to estrogen and NGF differentially regulated the expression of the two NGF receptor mRNAs. The expression of trkA mRNA was up-regulated, while p75NGFR mRNA was down-regulated transiently. The present data indicate that NGF may increase neuronal sensitivity to estrogen, and that estrogen, by differentially regulating p75NGFR and trkA mRNA, may alter the ratio of the two NGF receptors, and, consequently, neurotrophin responsivity. In view of the widespread co-localization of estrogen and neurotrophin receptor systems in the developing CNS, the reciprocal regulation of these receptor systems by NGF and estrogen may have important implications for processes governing neural maturation and the maintainance of neural function.

Androgenic regulation of expression of beta-tubulin messenger ribonucleic acid in motoneurons of the spinal nucleus of the bulbocavernosus

Expression of beta-tubulin mRNA was examined in androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in adult male rats by in situ hybridization histochemistry using cDNA encoding mouse beta-tubulin. Hybridizable beta-tubulin mRNA was localized in the somata and proximal dendrites of SNB motoneurons. Removal of androgen by castration significantly reduced the expression level of beta-tubulin mRNA in the SNB motoneurons, whereas the change was prevented by testosterone treatment. On the contrary, castration or testosterone treatment did not induce any changes in the expression level of beta-tubulin mRNA in the androgen-insensitive motoneurons of the retrodorsolateral nucleus. These results suggest that androgen regulates the expression of beta-tubulin gene in the SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally-induced neuronal plasticity in the SNB motoneurons.

An aromatase-associated cytoplasmic inclusion, the "stigmoid body," in the rat brain: II. Ultrastructure (with a review of its history and nomenclature)

The ultrastructure of aromatase-associated "stigmoid (dot-like) structures," which were detected in a previous study using light-microscopic immunohistochemistry (Shinoda et al.: J. Comp. Neurol. 322:360-376, '92), were examined in the rat medial preoptic region, bed nucleus of the stria terminalis, medial amygdaloid nucleus, and arcuate nucleus by pre- and post-embedding marking with a polyclonal antibody against human placental antigen X-P2 (hPAX-P2) for immuno-electron microscopic analysis. The immunoreactive stigmoid structure was identified as a distinct, non-membrane-bounded cytoplasmic inclusion (approximately 1-3 microns in diameter), which has a granulo-fuzzy texture with moderate-to-low electron density in non-immunostained preparations. It consists of at least four distinct granular and three distinct fibrillo-tubular elements forming a granulo-fibrillar conglomerate. This type of inclusions was formally termed the "stigmoid body" under the electron microscope. The stigmoid body is composed of the outer granulo-fibrillar and inner hyaloplasmic compartments. The immunoreactivity for hPAX-P2 is mainly localized to the former, especially to the low density granulo-fuzzy materials associated with the fibrillo-tubular elements. Identification of the ultrastructure of stigmoid body clarified their prevalence not only in the limbic and hypothalamic regions, but also in sex-steroid-sensitive peripheral tissues (e.g., peripheral sensory ganglia, ovary, testis) by consulting earlier electron-microscopic studies. Reviewing the history and nomenclature of this inclusion body, we reorganized the terminology of related neuronal cytoplasmic inclusions, the terms of which have often been confused, and discussed its functional significance on the basis of the present and previously accumulated data. In conclusion, we emphasized the importance of the stigmoid bodies in the sex-steroid-sensitive neural system because of their large size, high frequency, specific distribution in brains and peripheral tissues, effects of sex-steroids, and immunological and histochemical characteristics of the antibody marking the inclusion. The stigmoid bodies may provide a subcellular site for sex-steroid metabolism in their target tissues and play a critical role in cytosolic modulation of their actions (e.g., by aromatization) prior to their receptor binding.

Effect of androgen on the expression of gap junction and beta-actin mRNAs in adult rat motoneurons

Expression of gap junction and beta-actin mRNAs was examined in androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in adult male rats by in situ hybridization histochemistry using complementary DNAs encoding rat liver gap junction protein (connexin 32) and chick beta-actin. Hybridizable gap junction and beta-actin mRNAs were localised on the somata and proximal dendrites of SNB motoneurons. Removal of androgen by castration significantly reduced the expression levels of both gap junction and beta-actin mRNAs in the SNB motoneurons, whereas these changes were prevented by testosterone treatment. On the contrary, castration or testosterone treatment did not induce any changes in the expression levels of gap junction and beta-actin mRNAs in the motoneurons of the retrodorsolateral nucleus (RDLN), which accumulate androgen less frequently and sparsely than those in the SNB. These results suggest that androgen regulates the expression of both gap junction and beta-actin genes in the SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally induced neuronal plasticity in the SNB motoneurons.

Differential hormonal modulation of brain antigens recognized by the AB-2 monoclonal antibody

The expression of monoclonal antibody AB-2 immunoreactivity is age- and sex-dependent in radial glia of developing rat hypothalamus and is regulated by prenatal exposure to gonadal steroids. In the present study, several proteins were recognized by AB-2 and were distributed selectively in subcellular fractions from neonatal hypothalamus (HYP), remaining forebrain (FB), and brainstem regions. Immunoblots revealed polypeptide bands in 3 major molecular weight classes: one at approximately 195 kDa in the cytosolic compartment; and two doublets at 220 kDa and 340 kDa in both microsomal and crude mitochondrial membrane fractions. The 220 kDa and 340 kDa doublets were also Triton-insoluble, suggesting a cytoskeletal association. The 195 kDa-AB-2-immunoreactive band was present in both Triton-soluble and insoluble fractions. AB-2 also recognized several acidic glycolipids extracted from postnatal rat brain regions on immunoblots following high performance thin layer chromatography. One of the bands from postnatal rat brain extracts migrated similarly to purified bovine brain sulfatide, which was also immunoreactive with AB-2. AB-2 immunoreactivity with proteins, polar lipids, and sulfatide suggests that the epitope is a carbohydrate present in multiple cellular compartments. AB-2 recognized the same molecular bands in males and females. Testosterone treatment selectively decreased the level of the 195 kDa AB-2-immunoreactive polypeptide. The 195 kDa AB-2-immunoreactive polypeptide possibly acts in radial glia in the determination of sexually dimorphic neurons in the preoptic area/hypothalamus.

Synaptogenic action of sex steroids in developing and adult neuroendocrine brain

Sex steroids exert potent influences on modulating neural development and neural circuit formation in both developing and adult sex steroid-sensitive neuroendocrine brain. During development, estrogen or aromatizable androgen can act as a neurotropic factor on neural tissues, stimulating axonal and dendritic growth and synapse formation. The development of sexual dimorphic synaptic organization may reflect sex steroid-modulating synaptogenesis in the hypothalamus and limbic system during the perinatal period. The onset of puberty also may be due, at least in part, to stimulation of synapse formation by estrogen in the hypothalamus. In adulthood, estrogen has a facilitatory effect on synapse formation in neural structures such as septum, hypothalamus and midbrain with or without brain lesions, and androgen plays a significant role in regulating synaptic remodeling in the androgen-sensitive spinal motoneuron pools. Thus, sex steroids seems to be critical from the developmental period to adulthood for organizing and reorganizing the neuronal circuitry driving neuroendocrine and behavioral functions.

Organotypic culture of the developing cerebral cortex and hypothalamus: relevance to sexual differentiation

Addition of estradiol to organotypic cultures of the rodent hypothalamus, preoptic area and cerebral cortex elicits a striking enhancement of neurite growth which is restricted to estrogen receptor-containing regions of the explants. The morphogenetic consequences of enhanced neurite growth help explain the origin of structural sexual dimorphisms in the CNS. Neurite enhancement may result from both neuronotrophic and growth-promoting actions of steroids. Steroid effects may be mediated by interactions with endogenous growth factors or their receptors. Growth-promoting effects of steroids on the developing cerebral cortex, in particular, may have relevance for sexual differentiation of cognitive functions.

Gender and gonadectomy influence specific proteins in the cerebellar cortex of the adult rat: a two-dimensional gel electrophoretic analysis

Two-dimensional polyacrylamide gel electrophoresis was used to determine the influence of gender and gonadectomy on individual proteins of the 105,000 g supernatant (cytosol) of the cerebellar cortex of the adult rat. At age 60 days were gonadectomized or sham-gonadectomized. At age 140 days the rats were sacrificed and the 105,000 g supernatant prepared from the cerebellar cortex. Sham-operated female rats were sacrificed during the proestrus stage of the estrous cycle. Out of 200 proteins identified, 13 were influenced by gender and/or gonadectomy. Five of these proteins were influenced by both gender and gonadectomy. A total of 18 differences were observed. Apparent molecular weights and isoelectric points (pIs) for the 13 proteins ranged from 22,000 to 92,000 Da and pH 4.8-6.1, respectively. Sex differences occurred in the percent volumes (spot density) of 9 proteins between intact male and proestrous female rats. Sex differences in 4 proteins were not influenced by gonadectomy. These differences were presumed to be genetically programmed and/or to reflect the permanent organizational effects of gonadal steroids on the genome. Differences in the remaining 5 proteins depend upon the transient activational effects of the testicular sex steroids, i.e. these gender differences were eliminated by castration. The effects of gonadectomy on individual proteins were gender specific, i.e. proteins affected by ovariectomy were not influenced by castration and vice versa. This suggests intact gonads are required for the specific gender-dependent proteins identified in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal changes in actin mRNA levels and incorporation of 35S-methionine into actin in the rat hypothalamus

1. The in vitro incorporation of 35S-methionine into actin and total soluble proteins, as well as the levels of actin mRNA, were studied in the hypothalamus and frontal cerebral cortex of adult male rats killed at six different time intervals during a 24-hr cycle. 2. The specific activity of total soluble proteins after labeled methionine incubations did not vary as a function of time of day in any of the examined brain regions. 3. The incorporation of 35S-methionine into a 43-kDa protein, corresponding to the electrophoretic mobility of actin, varied diurnally in the hypothalamus, exhibiting a maximum at 1200 hr. Such a diurnal variation was not found in frontal cerebral cortex. 4. Similar results were obtained when labeled methionine incorporation into actin was assessed in hypothalamus and cerebral cortex by an immunoprecipitation procedure. 5. An increase in actin hypothalamic mRNA levels, quantitated by dot-blot analysis, was found at 0800, 4 hr in advance to the maximum in 35S-methionine incorporation to actin. 6. The levels of actin mRNA did not vary significantly as a function of time of day in the frontal cerebral cortex.

The molecular mode of brain mRNA processing damage followed by the suppression of post-transcriptional poly(A) synthesis with cordycepin

Complete suppression of polyadenylation of nuclear precursors of rat brain mRNA by cordycepin leads to degradation of some translatable sequences of both poly(A)(+)- and poly(A)- pre-mRNA localized in 80S hnRNP-particles. This fact has been established by comparative analysis of the data of two-dimensional gel-electrophoretic mapping of translation products synthesized in reticulocytic cell-free system using the exogenous purified templates of rapidly labelling translatable 9-17S hn RNA (pre-mRNA) isolated from brain 80S hn RNP particles of experimental (4 hrs after cordycepin injection) and control (injection of physiological solution) adult healthy male rats. Long contact of brain cells with cordycepin (4 or more hrs) creates conditions for formation of hnRNP-particles devoid of poly(A)+ RNA and poly(A)-binding proteins. These particles differ from "normal" ones by the value of the RNA/protein ratio, and by considerably lower resistance to the action of exogenous ribonucleases and endogenous RNase. Cordycepin does not have a direct effect on biosynthesis of nuclear poly(A)-binding proteins within the duration of the experiment (8 hrs). The phenomena described are discussed.

Time-dependent effect of melatonin on actin mRNA levels and incorporation of 35S-methionine into actin and proteins by the rat hypothalamus

The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of 35S-methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10:00 or 18:00. Injection of 100 micrograms/kg of melatonin for ten days at either time induced a significant depression in the incorporation of 35S-methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 micrograms/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot-blot analysis, decreased only after the injection of 100 micrograms/kg melatonin for ten days at 10:00. Neither a 10-micrograms/kg dose of melatonin, nor a single injection of 100 micrograms/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 micrograms/kg for ten days) did not modify hypothalamic somatostatin or H-Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic actin synthesis.

Novel electrophoretic approach to study of poly(A)+RNA pool heterogeneity in different areas of human postmortem brain

A simple method for fast fractionation of human postmortem brain total poly(A)+RNA has been developed. Guanidine thiocyanate extractable RNA was directly applied on the membranes of cellulose nitrate with immobilized oligo(dT) chains. After the electrophoresis in 35 mM tris-acetete buffer (pH 7.90) containing 10 mM EDTA and 35% formamide, the membranes were washed with the same buffer for removal of nonbinding poly(A)-lacking RNAs. Then, poly(A)+RNA fractions were selectively stained by 3,5-dimethylphenol in the presence of FeCl3 at pH 2.35. Finally, the resulting electrophorograms were scanned at 500 nm for quantitative evaluation of the data.

Brain protein changes during development and sexual differentiation in the rat

Subcellular fractions were prepared from the hypothalamus-preoptic area and the 'remainder of the brain' of intact male and female rats at 0, 8, 25 and 72 days of age. Proteins associated with each fraction were subjected to SDS-PAGE chromatography and stained with Coomassie Brilliant Blue. Developmental changes were found to occur in proteins associated with the soluble (14,600, 15,000, 29,900, 38,900 and 49,000 mol. wt), nuclear (40,000-50,000 and 13,800-16,000 mol. wt.), mitochondrial-lysosomal (49,000-52,000 mol. wt.) and microsomal (14,400, 20,000, 50,100, 56,900 and 130,000 mol. wt.) fractions. In addition, soluble proteins were greater in males than in females at days 0 (53,000-56,000 mol. wt.; probably tubulin) and 25 (14,600 and 15,000 mol. wt.). These changes in brain proteins probably reflect important structural and functional changes that occur during maturation and sexual differentiation of the brain.