Genetic Sex Differences in Early Human Neuronal Development : An Investigation in Embryo Tissue and Embryonic Stem Cells

Sex differences in the human body affect many different organs and tissues, some of them have an effect on the human brain and its development. In the developing nervous system, sex differences can bias the number or functionality of neurons, glial cells or synapses. As a result, neural networks might develop with a sex-specific bias. A number of neurodevelopmental diseases, such as Tourette-Syndrome or Attention-Deficit/Hyperactivity Disorder, show sex differences in symptoms, onset and prevalence. It seems likely that sex differences in brain development contribute to differences in neurological disease susceptibility between males and females. In my work, I am investigating sex differences in gene expression during neuronal development in human embryo brain tissue, embryonic stem cells and neural stem cells. Of particular interest for sex differences are the genes of the sex chromosomes, since a large number of X-linked genes and even some Y-linked genes are implicated in neurodevelopment. In our first study, we found that Y chromosome genes are highly expressed in fetal brain tissues and 5 X/Y homologous genes have an increased gene dosage in male samples. We suggest 6 novel long non-coding RNAs that were expressed in previously unannotated regions of the Y chromosome in male fetal brain tissue. In our second study, we identified an increased rate of proliferation in male neural stem cells but similar neuronal differentiation trajectories in cells of both sexes. An increased expression of DCX and DLG4 suggests a faster differentiation of male neural stem cells, but sex differences disappeared after 14 days. Male cells overexpressed MASH1 and RELN, markers for Cajal-Retzius neurons, and the two demethylases KDM5D and UTY. Female cells overexpressed RMST a long non-coding RNA critical for neurogenesis. In the third study, sex-biased gene expression was investigated in human embryonic stem cells during 37 days of neuronal differentiation. Male and female cell lines showed sex-biased expression of genes involved in neurodevelopment, suggesting a sex difference in differentiation trajectory. We propose 13 sex-biased candidate genes that could strongly affect neuronal development. In addition, we confirmed the gene dosage compensation of X/Y homologs escaping XCI through the Y-homolog and identified a significant expression of the Y-homologs TXLNGY and UTY after 37 days of neuronal differentiation. We have also measured a significant increase of the Y-linked genes PCDH11Y, UTY and USP9Y during differentiation. The fourth study was an investigation of sex differences in H3 methylation and acetylation marks in embryonic stem cells. We found that H3K4me3, a transcription activation mark, was enriched at promotor sites of major pluripotency genes and related pathways, in female cell lines. In conclusion, we confirm the importance of Y chromosome genes for neuronal development and show that sex differences in gene expression exist during neuronal differentiation

Genetic Sex Differences in Early Human Neuronal Development : An Investigation in Embryo Tissue and Embryonic Stem Cells

Sex differences in the human body affect many different organs and tissues, some of them have an effect on the human brain and its development. In the developing nervous system, sex differences can bias the number or functionality of neurons, glial cells or synapses. As a result, neural networks might develop with a sex-specific bias. A number of neurodevelopmental diseases, such as Tourette-Syndrome or Attention-Deficit/Hyperactivity Disorder, show sex differences in symptoms, onset and prevalence. It seems likely that sex differences in brain development contribute to differences in neurological disease susceptibility between males and females. In my work, I am investigating sex differences in gene expression during neuronal development in human embryo brain tissue, embryonic stem cells and neural stem cells. Of particular interest for sex differences are the genes of the sex chromosomes, since a large number of X-linked genes and even some Y-linked genes are implicated in neurodevelopment. In our first study, we found that Y chromosome genes are highly expressed in fetal brain tissues and 5 X/Y homologous genes have an increased gene dosage in male samples. We suggest 6 novel long non-coding RNAs that were expressed in previously unannotated regions of the Y chromosome in male fetal brain tissue. In our second study, we identified an increased rate of proliferation in male neural stem cells but similar neuronal differentiation trajectories in cells of both sexes. An increased expression of DCX and DLG4 suggests a faster differentiation of male neural stem cells, but sex differences disappeared after 14 days. Male cells overexpressed MASH1 and RELN, markers for Cajal-Retzius neurons, and the two demethylases KDM5D and UTY. Female cells overexpressed RMST a long non-coding RNA critical for neurogenesis. In the third study, sex-biased gene expression was investigated in human embryonic stem cells during 37 days of neuronal differentiation. Male and female cell lines showed sex-biased expression of genes involved in neurodevelopment, suggesting a sex difference in differentiation trajectory. We propose 13 sex-biased candidate genes that could strongly affect neuronal development. In addition, we confirmed the gene dosage compensation of X/Y homologs escaping XCI through the Y-homolog and identified a significant expression of the Y-homologs TXLNGY and UTY after 37 days of neuronal differentiation. We have also measured a significant increase of the Y-linked genes PCDH11Y, UTY and USP9Y during differentiation. The fourth study was an investigation of sex differences in H3 methylation and acetylation marks in embryonic stem cells. We found that H3K4me3, a transcription activation mark, was enriched at promotor sites of major pluripotency genes and related pathways, in female cell lines. In conclusion, we confirm the importance of Y chromosome genes for neuronal development and show that sex differences in gene expression exist during neuronal differentiation

Novel Y-Chromosome Long Non-Coding RNAs Expressed in Human Male CNS During Early Development

Global microarray gene expression analyses previously demonstrated differences in female and male embryos during neurodevelopment. In particular, before sexual maturation of the gonads, the differences seem to concentrate on the expression of genes encoded on the X- and Y-chromosomes. To investigate genome-wide differences in expression during this early developmental window, we combined high-resolution RNA sequencing with qPCR to analyze brain samples from human embryos during the first trimester of development. Our analysis was tailored for maximum sensitivity to discover Y-chromosome gene expression, but at the same time, it was underpowered to detect X-inactivation escapees. Using this approach, we found that 5 out of 13 expressed game to log pairs showed unbalanced gene dosage, and as a consequence, a male-biased expression. In addition, we found six novel non-annotated long non-coding RNAs on the Y-chromosome with conserved expression patterns in newborn chimpanzee. The tissue specific and time-restricted expression of these long non-coding RNAs strongly suggests important functions during central nervous system development in human males

Thioredoxin-80 protects against amyloid-beta pathology through autophagic-lysosomal pathway regulation

Aggregation and accumulation of amyloid beta (Aβ) are believed to play a key role in the pathogenesis of Alzheimer’s disease (AD). We previously reported that Thioredoxin-80 (Trx80), a truncated form of Thioredoxin-1, prevents the toxic effects of Aβ and inhibits its aggregation in vitro. Trx80 levels were found to be dramatically reduced both in the human brain and cerebrospinal fluid of AD patients. In this study, we investigated the effect of Trx80 expression using in vivo and in vitro models of Aβ pathology. We developed Drosophila melanogaster models overexpressing either human Trx80, human Aβ42, or both Aβ42/Trx80 in the central nervous system. We found that Trx80 expression prevents Aβ42 accumulation in the brain and rescues the reduction in life span and locomotor impairments seen in Aβ42 expressing flies. Also, we show that Trx80 induces autophagosome formation and reverses the inhibition of Atg4b-Atg8a/b autophagosome formation pathway caused by Aβ42. These effects were also confirmed in human neuroblastoma cells. These results give insight into Trx80 function in vivo, suggesting its role in the autophagosome biogenesis and thus in Aβ42 degradation. Our findings put Trx80 on the spotlight as an endogenous agent against Aβ42-induced toxicity in the brain suggesting that strategies to enhance Trx80 levels in neurons could potentially be beneficial against AD pathology in humans.GGL was the recipient of the Basque Government Postdoctoral Fellowship (POS 2015-1-0028). This research was supported by the following Swedish foundations: HP was supported by The Swedish Institute Visby Program and European Social Fund’s Doctoral Studies and Internationalization Programme DoRa carried out by Archimedes Foundation. Swedish Brain Power, the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet, Margaretha af Ugglas Foundation, Olle Engkvist Byggmästare Stiftelse, Gun och Bertil Stohnes Stiftelse, Loo och Hans Osterman Foundation, Karolinska Institutet fund for geriatric research, Stiftelsen Gamla Tjänarinnor, Alzheimerfonden, the Centre for Innovative Medicine and the Jonasson center at the Royal Institute of Technology (Sweden)