title: Sex-dimorphic gene expression and ineffective dosage compensation of Z-linked genes in gastrulating chicken embryos.
abstract: BACKGROUND
  Considerable progress has been made in our understanding of sex determination and dosage compensation mechanisms in model organisms such as C. elegans, Drosophila and M. musculus. Strikingly, the mechanism involved in sex determination and dosage compensation are very different among these three model organisms. Birds present yet another situation where the heterogametic sex is the female. Sex determination is still poorly understood in birds and few key determinants have so far been identified. In contrast to most other species, dosage compensation of bird sex chromosomal genes appears rather ineffective.
  
  
  RESULTS
  By comparing microarrays from 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 developed in our laboratory (called Manteia), show that among these male-biased genes found on the Z chromosome, more than 20 genes play a role in sex differentiation.
  
  
  CONCLUSIONS
  These results corroborate previous studies demonstrating the rather inefficient dosage compensation for Z chromosome in birds and show that this sexual dimorphism in gene regulation is observed long before the onset of sexual differentiation. These data also suggest a potential role of non-compensated Z-linked genes in somatic sex differentiation in birds.
authors.affiliation: Stowers Institute for Medical Research, 1000 E, 50th Street, Kansas City, MO 64110, USA.
authors.forename: Shaobing O
authors.initials: SO
authors.lastname: Zhang
authors.forename: Sachin
authors.initials: S
authors.lastname: Mathur
authors.forename: Gaye
authors.initials: G
authors.lastname: Hattem
authors.forename: Olivier
authors.initials: O
authors.lastname: Tassy
authors.forename: Olivier
authors.initials: O
authors.lastname: Pourquié
mesh_terms: D000818:Animals; D002642:Chick Embryo / Q000196:embryology*; D004303:Dosage Compensation, Genetic; D005260:Female; D054262:Gastrulation; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D012727:Sex Characteristics; D012730:Sex Chromosomes / Q000235:genetics