Sex-dimorphic gene expression and ineffective dosage compensation of Z-linked genes in gastrulating chicken embryos
Ontology highlight
ABSTRACT: Sex determination is still poorly understood in birds and no key determinants have so far been identified. In contrast to most other species, dosage compensation of bird sex chromosomal genes appears rather ineffective. By comparing microarrays of microdissected primitive streak from single chicken embryos, we identified a large number of genes differentially expressed between male and female embryos at a very early stage (Hamburger and Hamilton stage 4), long before any sexual differentiation occurs. Most of these genes are located on the Z chromosome, which indicates that dosage compensation is ineffective in early chicken embryos. Gene ontology analyses using an enhanced annotation tool for Affymetrix probesets of the chicken genome shows that among the male-biased genes found on the Z chromosome, more than 20 genes have a role in sex differentiation.
Project description:Sex determination is still poorly understood in birds and no key determinants have so far been identified. In contrast to most other species, dosage compensation of bird sex chromosomal genes appears rather ineffective. By comparing microarrays of microdissected primitive streak from single chicken embryos, we identified a large number of genes differentially expressed between male and female embryos at a very early stage (Hamburger and Hamilton stage 4), long before any sexual differentiation occurs. Most of these genes are located on the Z chromosome, which indicates that dosage compensation is ineffective in early chicken embryos. Gene ontology analyses using an enhanced annotation tool for Affymetrix probesets of the chicken genome shows that among the male-biased genes found on the Z chromosome, more than 20 genes have a role in sex differentiation. Experiment Overall Design: Primitive streak tissues were dissected out of individual Hamburger and Hamilton (HH) stage 4 chicken embryos and extracted for total RNA. Total RNA was amplified 2-cycles, biotin-labeled and hybridized to Affymetrix chicken GeneChip. Gene expression profiles of female and male samples were analyzed for sex-dimorphic expression.
Project description:Gene dosage imbalance of heteromorphic sex chromosomes (XY or ZW) exists between the sexes, and with the autosomes. Mammalian X chromosome inactivation was long thought to imply a critical need for dosage compensation in vertebrates. However, mRNA abundance measurements that demonstrated sex chromosome transcripts are neither balanced between the sexes or with autosomes in monotreme mammals or birds brought sex chromosome dosage compensation into question. This study examines transcriptomic and proteomic levels of dosage compensation in platypus and chicken compared to mouse, a model eutherian species. We analyzed mRNA and protein levels in heart and liver tissues of chicken, mouse and platypus.
Project description:The contrasting dose of sex chromosomes in males and females potentially introduces a large-scale imbalance in levels of gene expression between sexes. In many organisms dosage compensation has thus evolved to equalize sex-linked gene expression in males and females1,2, in mammals achieved by X chromosome inactivation and in flies and worms by up- or down-regulation of X-linked expression, respectively. Another form of dosage compensation ensures that expression levels on the X chromosome and on autosomes are balanced3,4. While otherwise widespread in systems with heteromorphic sex chromosomes, the case of dosage compensation in birds (males ZZ, females ZW) remains an unsolved enigma5,6. Here we use a microarray approach to show that male day 18 chicken embryos generally express higher levels of Z-linked genes than female birds, both in soma and in gonads. The distribution of male-to-female fold-change values for Z chromosome genes is wide and has a mean of 1.4-1.6, which is consistent with absence of dosage compensation and sex-specific feedback regulation of gene expression at individual loci2. Intriguingly, without global dosage compensation, female chicken has significantly lower expression levels of Z-linked compared to autosomal genes, which is not the case in male birds. The pronounced sex difference in gene expression is likely to contribute to sexual dimorphism among birds, and potentially has implication to avian sex determination. Keywords: dosage compensation, sex-biased gene expression, soma and gonad
Project description:The egg teeth of chicken of the developmental stage 36 according to Hamburger and Hamilton (about 10 days of egg incubation at 37 °C) were sampled to investigate the protein composition of the egg tooth.
Project description:Formation of blood vessels requires the concerted regulation of an unknown number of genes in a spatial-, time- and dosage-dependent manner. We investigated vascular development in vivo by determining global gene regulation throughout the formation of the chick chorio-allantoic membrane (CAM). Our study provides a comprehensive molecular map of vascular maturation during developmental angiogenesis and might thus be a valuable resource to streamline further research of candidates susceptible to mediate pathological angiogenesis. Experiment Overall Design: The developmental stage of the embryos was determined after isolation of the CAM according to Hamburger & Hamilton (HH) (1992). CAMs were isolated from embryos at developmental day E5 (HH26), E7 (HH30), E10 (HH>35) and E14 (HH40), (n=3 embryos/day). mRNA was isolated and hybridized to Affymetrix chicken GeneChips using the Affymetrix standard protocol. We compared one embryo at a lower HH stage to three embryos at a more advanced HH stage and repeated the comparison with two more embryos. Overall, we compared expression between E7 and E5, E10 and E5, E14 and E5, E10 and E7 and E14 and E10.
Project description:We have performed a comparison of global patterns of gene expression between two bird species, the chicken and zebra finch, especially with regard to sex bias of autosomal vs. Z chromosome genes, dosage compensation and evolution of sex bias. Both species appear to lack a Z chromosome-wide mechanism of dosage compensation, because both have a similar pattern of significantly higher expression of Z genes in males relative to females. Unlike the chicken Z chromosome, which has female-specific expression of the non-coding RNA MHM (male hypermethylated), and acetylation of histone 4 lysine 16 (H4K16) near MHM, the zebra finch Z chromosome appears to lack the MHM sequence and acetylation of H4K16. The zebra finch also does not show the reduced male to female (M:F) ratio of gene expression near MHM similar to that found in the chicken. Although the M:F ratios of Z chromosome gene expression are similar across tissues and ages within each species, they differ between the two species. Z genes showing the greatest species difference in M:F ratio were concentrated near the MHM region of the chicken Z chromosome. The current study shows that the zebra finch differs from the chicken because it lacks a specialized region of greater dosage compensation along the Z chromosome, and shows dosage compensation for a different set of Z genes than the chicken. These patterns suggest that different avian taxa may have evolved specific compensatory mechanisms.
Project description:Neural cest cells are a transient stem cell-like population appearing during vertebrate embryonic development. Generation of the cranial neural crest is known to require a balanced combination of FGF and BMP levels. However, it is poorly understood how the functions of such growth factors are controlled in the extracellular spaces. Here we identifiy the extracelluar matrix protein anosmin (Gga.14976.1.S1_at, clone ChEST132d10) as a novel molecule synthesized locally in the cranial neural crest of chicken embryos. Cranial neural folds (NF) and ventral neural plates (NP) were dissected from Hamburger & Hamilton stage 8 (HH8) embryos (80 to 14 embryos, n=4), and total RNA was analyzed using a GeneChip chicken genome arrays (Affymetrix)
Project description:Sexual dimorphism depends on sex-biased gene expression, but the contributions of microRNAs (miRNAs) have not been globally assessed. We therefore produced an extensive small RNA sequencing dataset to analyse male and female miRNA expression profiles in mouse, opossum and chicken. Our analyses uncovered numerous cases of somatic sex-biased miRNA expression, especially in the mouse heart and liver. Sex-biased expression is explained by miRNA-specific regulation, including sex-biased chromatin accessibility at promoters, rather than piggybacking of intronic miRNAs on sex-biased protein-coding genes. In mouse, but not opossum and chicken, sex bias is coordinated across tissues such that autosomal testis-biased miRNAs tend to be somatically male-biased, whereas autosomal ovary-biased miRNAs are female-biased, possibly due to broad hormonal control. In chicken, which has a Z/W sex chromosome system, expression output of genes on the Z chromosome is expected to be male-biased, since there is no global dosage compensation mechanism that restores expression in ZW females after almost all genes on the W chromosome decayed. Nevertheless, we found that the dominant liver miRNA, miR-122-5p, is Z-linked but expressed in an unbiased manner, due to the unusual retention of a W-linked copy. Another Z-linked miRNA, the male-biased miR-2954-3p, shows conserved preference for dosage-sensitive genes on the Z chromosome, based on computational and experimental data from chicken and zebra finch, and acts to equalise male-to-female expression ratios of its targets. Unexpectedly, our findings thus establish miRNA regulation as a novel gene-specific dosage compensation mechanism.
Project description:We have performed a comparison of global patterns of gene expression between two bird species, the chicken and zebra finch, especially with regard to sex bias of autosomal vs. Z chromosome genes, dosage compensation and evolution of sex bias. Both species appear to lack a Z chromosome-wide mechanism of dosage compensation, because both have a similar pattern of significantly higher expression of Z genes in males relative to females. Unlike the chicken Z chromosome, which has female-specific expression of the non-coding RNA MHM (male hypermethylated), and acetylation of histone 4 lysine 16 (H4K16) near MHM, the zebra finch Z chromosome appears to lack the MHM sequence and acetylation of H4K16. The zebra finch also does not show the reduced male to female (M:F) ratio of gene expression near MHM similar to that found in the chicken. Although the M:F ratios of Z chromosome gene expression are similar across tissues and ages within each species, they differ between the two species. Z genes showing the greatest species difference in M:F ratio were concentrated near the MHM region of the chicken Z chromosome. The current study shows that the zebra finch differs from the chicken because it lacks a specialized region of greater dosage compensation along the Z chromosome, and shows dosage compensation for a different set of Z genes than the chicken. These patterns suggest that different avian taxa may have evolved specific compensatory mechanisms. Experimental groups: Post-hatch Days 1, 25, 45, and 90+ for both Females and Males (d1_F, d1_M, d25_F, d25_M, d45_F, d45_M, adult_F, adult_M). Biological replicates: 6 per group. One test developmental stage subject and one universal SoNG reference (pooled Taeniopygia guttata brain) per array.