Molecular Psychiatry (2009) 14, 988–991 & 2009 Nature Publishing Group All rights reserved 1359-4184/09 $32.00 www.nature.com/mp LETTERS TO THE EDITOR Prenatal sex differences in the human brain Molecular Psychiatry (2009) 14, 988–989. doi:10.1038/ development. These genes are not only expressed in mp.2009.79 the brain before birth but some of them are also known to have sex differences in adult brain,1,4 whereas others are expressed during infancy, but The presence of genetic sex differences in the adult reduced later on during their lifetime.5 human brain is now recognized.1 We hypothesized Intriguingly, SRY, a well-known determinant of that the basis of this sex bias is already established in testicle development during midgestation,6 showed the brain before birth. Here, we show that several no evidence of expression in any of the brain regions genes encoded in the Y-chromosome are expressed in analyzed (Figure 1b, and Supplementary Figure 1), many regions of the male prenatal brain, likely having suggesting that the main somatic sex determinants functional consequences for sex bias during human may be different for the brain and gonads during brain development. human gestation. The marked sex differences in age at onset, In humans, all 11 genes described here are encoded prevalence and symptoms for numerous neuropsy- in the male-specific region of the Y-chromosome,7 chiatric disorders2 indicate the importance to study with RPS4Y1 and ZFY located in the p-arm very close the emergence of a sex bias during human brain to SRY and most of the remaining genes located in the development. A recent article includes for the first q-arm. Interestingly, the expression of Y-linked genes time comprehensive data on the human brain tran- scriptome before birth.3 This elegant work reveals a large number of gene and alternative splicing differ- ences specific to certain regions of the brain during development. A total of 12 regions in the midgesta- tion human brain were analyzed in both male and 10 female human fetal brain specimens. This data set provides for the first time the opportunity to evaluate 8 the existence of embryonic sex bias in the human 6 brain. To do this, we re-analyzed human fetal brain expression expression data from the Gene expression Omnibus 2 log 4 (GEO accession GSE 13344, Human Exon 1.0 ST Array) according to sex. The database included 95 2 array hybridizations, of which 72 corresponded with different brain regions from three midgestation female UTY ZFY SRY PRKY DDX3YUSP9Y EIF1AY fetuses and 23 were from equivalent brain regions RPS4Y1 NLGN4Y TMSB4Y PCDH11Y CYorf15B from a male. The largest sex differences observed male female (ind.1,2,3) mean bg were in genes encoded on the Y-chromosome, show- ing the existence of prenatal gender bias in brain Figure 1 Expression of Y-linked genes in male prenatal expression. Figure 1a shows the expression levels of brain. (a) Identification of 11 Y-linked genes that are 11 Y-chromosome-encoded genes, including RPS4Y1, expressed in the male prenatal brain. The genes were PCDH11Y, DDX3Y, USP9Y, NLGN4Y, EIF1AY, UTY, identified by comparing microarray measurements of mRNA levels in 12 different brain regions in prenatal male ZFY, TMSB4Y, CYorf15B and PRKY. For 10 genes out brain (yellow, n = 23) and in prenatal female brain (blue, of these 11, expression was detected in all the 12 arrays narrays = 72). As female samples do not contain Y-linked brain regions analyzed (Supplementary Figure 1), genes, the signals obtained in females were used as suggesting that they may be present throughout the measurements of the local probe background level for each whole brain during development. PRKY on the other individual Y-linked gene, and the criterion for expression hand was expressed in a more restricted manner in was a mean fold-change of at least two as compared with the the cortex samples, with low expression in cerebel- female signals. (b) SRY did not show evidence of expression lum and basal ganglia. Some evidence of specific in any of the male prenatal brain samples. The band on the splice variant expression was found. For example, box represents the median, and the lower and upper hinge only one out of three ZFY transcripts produced of the box represent the first and third quartile. Whiskers designate the most extreme data points which are no more positive signals in cortex, striatum and thalamus than 1.5 times the interquartile range from the box. Round (Supplementary Figure 1). circles show outliers. The horizontal dashed line represents The expression of more than one-third of the genes the overall mean signal level of all Y-linked genes in encoded on the Y-chromosome in prenatal human females, shown as an indicator of the global background brain indicates their importance for sex-biased brain signal levels in the arrays. Letters to the Editor 989 in prenatal brain is only partially conserved between rodents and humans. USP9Y, DDX3Y and UTY have Stem cell signaling in known orthologous genes in the mouse Y-chromo- some, and their expression is conserved in terms of newly diagnosed, sex bias prenatally in both groups.8 Other genes with antipsychotic-naive prenatal sex bias in humans, such as RPS4Y1 and EIF1AY, have rodent homologs encoded in somatic subjects with nonaffective chromosomes and are not known to be sexually dimorphic. PCDH11Y and CYorf15B only have known psychosis mouse homologs in the X-chromosome and are not known to have sex differences in the brain. TMSB4Y and NLGN4Y lack known homologous in rodents. Molecular Psychiatry (2009) 14, 989–991. doi:10.1038/ Finally, ZFY, which encodes for a transcription factor mp.2009.45 in the Y-chromosome in both groups, is expressed in human brain before birth, but absent in prenatal mouse brain.8 The differences in prenatal expression Widespread metabolic abnormalities have been de- of Y-linked genes mentioned above suggest that parts scribed in newly diagnosed, antipsychotic-naive of the programming of gender biases in the brain are patients with nonaffective psychosis, including a human-, or at least, primate-specific. shorter telomere,1 abnormal glucose tolerance,2 an Although the importance of X-chromosome-encoded increase in the pro-inflammatory molecule interleu- genes for mental function has been well established,9 the kin-62 and an increased pulse pressure.1 Stromal- relevance of Y-chromosome genes on brain function is derived factor 1-alpha (SDF-1a), the major chemokine less known. The results presented here, together with for adult stem cells (SCs), is involved in glucose the well-known rapid evolution of Y-chromosomes,10 regulation3 and is abnormal in diabetes.4 SDF1 is clearly point to the importance of future investigation critical in homing, maintenance and mobilization of on Y-linked gene function in the developing human adult SCs.5 We tested the hypothesis that newly brain. diagnosed, antipsychotic-naive patients with nonaf- fective psychosis would have a decreased concentra- tion of circulating SDF-1a compared with control Conflict of interest subjects. The authors declare no conflict of interest. The psychosis (N = 24) and control (N = 24) subjects were matched for race (Caucasian), gender, B Reinius and E Jazin age, body mass index, smoking habit, cortisol blood Department of Development & Genetics, Evolutionary levels, socioeconomic status and catchment area Biology Centre, Uppsala University, Uppsala, Sweden (Table 1). The two groups were matched before E-mail: [email protected] or assaying SDF-1a concentrations. All subjects were [email protected] interviewed using the Structured Clinical Interview for DSM-IV Axis I Disorders. Psychopathology was rated using the Positive and Negative Syndromes References Scale (PANSS). Subjects in the psychosis group had a 1 Reinius B, Saetre P, Leonard JA, Blekhman R, Merino-Martinez R, maximum lifetime antipsychotic exposure of 1 week Gilad Y et al. PLoS Genet 2008; 4: e1000100. and no antipsychotic use in the 30 days before the 2 Paus T, Keshavan M, Giedd JN. Nat Rev Neurosci 2008; 9: study, and had a diagnosis of nonaffective psychosis. 947–957. Exclusion criteria for the control subjects included a 3 Johnson MB, Kawasawa YI, Mason CE, Krsnik Z, Coppola G, Bogdanovic D et al. Neuron 2009; 62: 494–509. history of psychosis or major depressive disorder. 4 Galfalvy HC, Erraji-Benchekroun L, Smyrniotopoulos P, Pavlidis P, Additional general inclusion criteria were age from Ellis SP, Mann JJ et al. BMC Bioinformatics 2003; 4:37. 18 to 64 years, no history of serious medical or 5 Weickert CS, Elashoff M, Richards AB, Sinclair D, Bahn S, Paabo S neurological condition and not using any medication et al. Mol Psychiatry 2009; 14: 558–561. 6 Maatouk DM, Capel B. Curr Top Dev Biol 2008; 83: 151–183. that impacts glucose tolerance. All subjects gave 7 Skaletsky H, Kuroda-Kawaguchi T, Minx PJ, Cordum HS, Hillier L, informed consent for participation in the study, Brown LG et al. Nature 2003; 423: 825–837. which was conducted under the supervision of the 8 Xu J, Burgoyne PS, Arnold AP. Hum Mol Genet 2002; 11: local institutional review board. 1409–1419. Blood was drawn between 0800 and 0900 hours 9 Skuse DH. Hum Mol Genet 2005; 14(Spec No 1): R27–R32. 10 Goto H, Peng L, Makova KD. J Mol Evol 2009; 68: 134–144. after an overnight fast. Plasma was collected on ice using EDTA and centrifuged for 15 min at 1000 Â g Supplementary Information accompanies the paper within 30 min of collection. An additional centrifuga- on the Molecular Psychiatry website (http://www. tion step of the separated plasma at 10 000 Â g for 1 nature.com/mp) 10 min at 2–8 C was performed for complete platelet removal.