Sexually dimorphic gene expression in the developing mouse gonad

Over the course of a few days, the bipotential embryonic mouse gonad differentiates into either a testis or an ovary. Though a few gene expression differences that underlie gonadal sex differentiation have been identified, additional components of the testicular and ovarian developmental pathways must be identified to understand this process. Here we report the use of a PCR-based cDNA subtraction to investigate expression differences that arise during gonadal sex differentiation. Subtraction of embryonic day 12.5 (E12.5) XY gonadal cDNA with E12.5 XX gonadal cDNA yielded 19 genes that are expressed at significantly higher levels in XY gonads. These genes display a variety of expression patterns within the embryonic testis and encode a broad range of proteins. A reciprocal subtraction (of E12.5 XX gonadal cDNA with E12.5 XY gonadal cDNA) yielded two genes, follistatin and Adamts19, that are expressed at higher levels in XX gonads. Follistatin is a well-known antagonist of TGFbeta family members while Adamts19 encodes a new member of the ADAMTS family of secreted metalloproteases.     

Sexually dimorphic expression of prepro-orexin mRNA in the rat hypothalamus

The neuropeptides orexin A and B are expressed in the lateral hypothalamic area and are involved in the regulation of energy homeostasis and arousal. Recent results showed gender differences in the expression of orexin receptor subtypes in rats. In the present study, we analyzed the mRNA expression of prepro-orexin (PPO) in the hypothalamus of male and female rats using quantitative real-time PCR. We found significantly higher levels of PPO mRNA in the hypothalamus of female rats compared to male rats. Our study indicates a sex-dependent regulation of hypothalamic PPO expression and suggests gender-specific functions of orexins.     

Sexually dimorphic androgen and estrogen receptor mRNA expression in the brain of túngara frogs

Sex steroid hormones are potent regulators of behavior and they exert their effects through influences on sensory, motor, and motivational systems. To elucidate where androgens and estrogens can act to regulate sex-typical behaviors in the túngara frog (Physalaemus pustulosus), we quantified expression of the androgen receptor (AR), estrogen receptor alpha (ERα), and estrogen receptor beta (ERβ) genes in the brains of male and females. To do so, we cloned túngara-specific sequences for AR, ERα, and ERβ, determined their distribution in the brain, and then quantified their expression in areas that are important in sexual communication. We found that AR, ERα, and ERβ were expressed in the pallium, limbic forebrain (preoptic area, hypothalamus, nucleus accumbens, amygdala, septum, striatum), parts of the thalamus, and the auditory midbrain (torus semicircularis). Males and females had a similar distribution of AR and ER expression, but expression levels differed in some brain regions. In the auditory midbrain, females had higher ERα and ERβ expression than males, whereas males had higher AR expression than females. In the forebrain, females had higher AR expression than males in the ventral hypothalamus and medial pallium (homolog to hippocampus), whereas males had higher ERα expression in the medial pallium. In the preoptic area, striatum, and septum, males and females had similar levels of AR and ER expression. Our results suggest that sex steroid hormones have sexually dimorphic effects on auditory processing, sexual motivation, and possibly memory and, therefore, have important implications for sexual communication in this system.     

Sexually dimorphic gene expression that overlaps maturation of type II pneumonocytes in fetal mouse lungs

Background  

In human, respiratory distress of the neonates, which occurs in prematurity, is prevalent in male. Late in gestation, maturation of type II pneumonocytes, and consequently the surge of surfactant synthesis are delayed in male fetuses compared with female fetuses. Although the presence of higher levels of androgens in male fetuses is thought to explain this sex difference, the identity of genes involved in lung maturation that are differentially modulated according to fetal sex is unknown. We have studied the sex difference in developing mouse lung by gene profiling during a three-day gestational window preceding and including the emergence of mature PTII cells (the surge of surfactant synthesis in the mouse occurs on GD 17.5).     

Sexually dimorphic expression of myosin heavy chains in the adult mouse masseter.

Little is known regarding the role of androgenic hormones in the maintenance of myosin heavy chain (MHC) composition of rodent masticatory muscles. Because the masseter is the principal jaw closer in rodents, we felt it was important to characterize the influence of androgenic hormones on the MHC composition of the masseter. To determine the extent of sexual dimorphism in the phenotype of masseter muscle fibers of adult (10-mo-old) C57 mice, we stained tissue sections with antibodies specific to type IIa and IIb MHC isoforms. Females contain twice as many fibers containing the IIa MHC as males, and males contain twice as many fibers containing the IIb MHC as females. There is a modest amount of regionalization of MHC phenotypes in the mouse masseter. The rostral portions of the masseter are composed mostly of type IIa fibers, whereas the midsuperficial and caudal regions contain mostly type IIb fibers. Using immunoblots, we showed that castration results in an increase in the expression of type IIa MHC fibers in males. Ovariectomy has no effect on the fiber type composition in females. We conclude that testosterone plays a role in the maintenance of MHC expression in the adult male mouse masseter.     

Sexually dimorphic expression of the sex chromosome-linked genes cntfa and pdlim3a in the medaka brain

In vertebrates, sex differences in the brain have been attributed to differences in gonadal hormone secretion; however, recent evidence in mammals and birds shows that sex chromosome-linked genes, independent of gonadal hormones, also mediate sex differences in the brain. In this study, we searched for genes that were differentially expressed between the sexes in the brain of a teleost fish, medaka (Oryzias latipes), and identified two sex chromosome genes with male-biased expression, cntfa (encoding ciliary neurotrophic factor a) and pdlim3a (encoding PDZ and LIM domain 3 a). These genes were found to be located 3–4 Mb from and on opposite sides of the Y chromosome-specific region containing the sex-determining gene (the medaka X and Y chromosomes are genetically identical, differing only in this region). The male-biased expression of both genes was evident prior to the onset of sexual maturity. Sex-reversed XY females, as well as wild-type XY males, had more pronounced expression of these genes than XX males and XX females, indicating that the Y allele confers higher expression than the X allele for both genes. In addition, their expression was affected to some extent by sex steroid hormones, thereby possibly serving as focal points of the crosstalk between the genetic and hormonal pathways underlying brain sex differences. Given that sex chromosomes of lower vertebrates, including teleost fish, have evolved independently in different genera or species, sex chromosome genes with sexually dimorphic expression in the brain may contribute to genus- or species-specific sex differences in a variety of traits.     

Developmental expression of MNAR mRNA in the mouse brain

During the development of the central nervous system, estrogen influences cellular differentiation and determines the functional connectivity of distinct neural networks. Estrogens generally act through nuclear estrogen receptors (ERs). Recent research has additionally revealed rapid estrogen effects requiring the binding of estrogen to membrane/cytoplasmic ERs and the activation of intracellular signaling systems such as the Src/MAPK cascade. The scaffold protein MNAR/PELP1 appears to be the designated functional mediator of such non-genomic estrogen effects between non-nuclear ERs and Src/MAPKs. In this study, we demonstrate the expression and differential regulation of MNAR mRNA in the developing male and female mouse brain by quantitative polymerase chain reaction. In the midbrain and hypothalamus, a gradual decline in MNAR mRNA levels has been observed prenatally with the highest values at embryonic day 15 and lowest at postnatal day 15. In the cortex, mRNA levels do not fluctuate until postnatal day 7 but decrease thereafter. No differences in MNAR expression between sexes have been detected. Analysis of neuronal and astroglia-enriched cell cultures has revealed the presence of MNAR in both cell types.     

Age does not alter protein kinase C isozymes mRNA expression in rat brain

Calcium and phospholipid dependent Protein kinase C (PKC) may play a role in memory function and pathogenesis of many neurodegenerative disorders such as Alzheimer's disease (AD). Abnormal phosphorylation by PKC as well as reduced levels of PKC has been implicated in the neurodegeneration associated with AD and aging. Recently, many subtypes of PKC isozymes have been identified by molecular biology techniques which are expressed differentially in various regions of the brain. The reduction and alterations in the activities and distribution of these subtypes of PKC isozymes may be accountable for the decline of selective neurons during aging. In order to investigate the role of PKC isozymes during aging, we examined the distribution of PKC-, , and mRNA, expressions between young (4 months) and old (25 months) rat brains using in situ hybridization histochemistry. Our studies showed that signals of three isoforms of PKC mRNA vary in cortical and hippocampal regions. However, no change was detected in any of the PKC isoforms mRNA expressions in aged animals.     

Trophectoderm-specific expression of the X-linked Bex1/Rex3 gene in preimplantation stage mouse embryos

The Bex1/Rex3 gene was recently identified as an X-linked gene that is differentially expressed between parthenogenetic and normal fertilized, preimplantation stage mouse embryos. The Bex1/Rex3 gene appears to be expressed preferentially from the maternal X chromosome in blastocysts, but from either X chromosome in later stage embryonic tissues and adult tissues. To investigate whether differential expression of the Bex1/Rex3 gene between normal and parthenogenetic blastocyst stage embryos reflects genomic imprinting at the Bex1/Rex3 locus itself, or instead is the result of preferential inactivation of the paternal X chromosome or differences in timing of cellular differentiation, we examined in detail the expression pattern of the Bex1/Rex3 mRNA in normal preimplantation stage embryos, and compared its expression between androgenetic, gynogenetic, and normal fertilized embryos. Expression data reveal that the Bex1/Rex3 gene is initially transcribed at the 2-cell stage, transiently induced at the 8-cell stage, and then increases in expression again at the blastocyst stage. Very little expression is observed in isolated inner cell masses, indicating selective expression in the trophectoderm. Comparisons of Bex1/Rex3 mRNA expression between male and female androgenetic and control embryos and gynogenetic embros failed to reveal any significant difference in expression between the different classes of embryos at the 8-cell stage, or the expanding blastocyst stage (121 hr post-hCG). At the late blastocyst stage (141 hr post-hCG), expression was significantly lower in XY control embryos as compared with XX controls. Bex1/Rex3 mRNA expression did not differ between XX and XY androgenones at the blastocyst stage or between gynogenones and XX control embryos. Thus, the Bex1/Rex3 gene does not appear to be regulated directly by genomic imprinting during the preimplantation period, just as it is not regulated by imprinting at later stages. Apparent differences in gene expression may arise through the effects of trophectoderm-specific expression coupled with differences in timing of trophectoderm differentiation between the different classes of embryos and effects of preferential paternal X chromosome inactivation (XCI).