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Sex-dimorphic gene expression and ineffective dosage compensation of Z-linked genes in gastrulating chicken embryos.

Zhang SO, Mathur S, Hattem G, Tassy O, Pourquié O - BMC Genomics (2010)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Stowers Institute for Medical Research, 1000 E, 50th Street, Kansas City, MO 64110, USA.

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.

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Male-biased gene expression. (a-g) HH4, dimorphic expression of PKCIW (a), PELOTA (b), FANCG (c), HSD17B4 (d), PGTER4 (e) and StARD (f). (a) and (b) are the same female and male embryos hybridized by the two different probes. In each panel, the embryo on the left is female and on the right is male.
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Figure 5: Male-biased gene expression. (a-g) HH4, dimorphic expression of PKCIW (a), PELOTA (b), FANCG (c), HSD17B4 (d), PGTER4 (e) and StARD (f). (a) and (b) are the same female and male embryos hybridized by the two different probes. In each panel, the embryo on the left is female and on the right is male.

Mentions: We performed in situ hybridizations to validate some of the female- and male-biased genes. The sex of embryos was ascertained by genotyping with PKCIW-based PCR before processing for in situ (Figure 4a). The expression patterns of two female-biased genes, PKCIW and thioredoxin-like 1 (TXNL1) were examined. Consistent with the microarray data and a previous report [15], PKCIW is constitutively expressed in females but not at all in males (Figure 4b and 4c). TXNL1, a Z-linked gene, is expressed 11 times more strongly in females than in males based on microarray analysis (Additional file 2). In situ hybridization indicates that it is expressed in females, but is almost undetectable in males (data not shown). To validate genes with an approximate two-fold expression difference between males and females, the following genes - PELOTA, FANCG, HSD17B4, PGTER4 and StARD4 - were randomly chosen to perform double in situ hybridization with a PKCIW-specific in situ probe. The PKCIW in situ signal was revealed first using Tyramide fluorescent substrate (Methods) to ascertain the sex of the embryo (Figure 5a). The stages of male and female samples were carefully identified based on morphology. Then, the in situ signals of stage-matched female to stage-matched male embryos were compared (Figure 5b-f) (see Methods). For each gene, four pairs of female/male samples in average were compared. At HH4, the stage when the microarray samples were prepared, both female and male embryos expressed these genes. The expression domains are largely in the anterior half of the embryo proper and are similar in females and males. However, males exhibited an apparent stronger staining (Figure 5b-f). We also analyzed their expression patterns at HH5 and HH6, when the head process and neural plate begin to take shape. In several of the genes, expression levels increase from HH4 to HH5. The dimorphic expression exists at these stages as well (data not shown). Interestingly, although the spatial patterns of most of the genes are somewhat different, the expression was usually highest in the head process and neural plate (data not shown).


Sex-dimorphic gene expression and ineffective dosage compensation of Z-linked genes in gastrulating chicken embryos.

Zhang SO, Mathur S, Hattem G, Tassy O, Pourquié O - BMC Genomics (2010)

Male-biased gene expression. (a-g) HH4, dimorphic expression of PKCIW (a), PELOTA (b), FANCG (c), HSD17B4 (d), PGTER4 (e) and StARD (f). (a) and (b) are the same female and male embryos hybridized by the two different probes. In each panel, the embryo on the left is female and on the right is male.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2821371&req=5

Figure 5: Male-biased gene expression. (a-g) HH4, dimorphic expression of PKCIW (a), PELOTA (b), FANCG (c), HSD17B4 (d), PGTER4 (e) and StARD (f). (a) and (b) are the same female and male embryos hybridized by the two different probes. In each panel, the embryo on the left is female and on the right is male.
Mentions: We performed in situ hybridizations to validate some of the female- and male-biased genes. The sex of embryos was ascertained by genotyping with PKCIW-based PCR before processing for in situ (Figure 4a). The expression patterns of two female-biased genes, PKCIW and thioredoxin-like 1 (TXNL1) were examined. Consistent with the microarray data and a previous report [15], PKCIW is constitutively expressed in females but not at all in males (Figure 4b and 4c). TXNL1, a Z-linked gene, is expressed 11 times more strongly in females than in males based on microarray analysis (Additional file 2). In situ hybridization indicates that it is expressed in females, but is almost undetectable in males (data not shown). To validate genes with an approximate two-fold expression difference between males and females, the following genes - PELOTA, FANCG, HSD17B4, PGTER4 and StARD4 - were randomly chosen to perform double in situ hybridization with a PKCIW-specific in situ probe. The PKCIW in situ signal was revealed first using Tyramide fluorescent substrate (Methods) to ascertain the sex of the embryo (Figure 5a). The stages of male and female samples were carefully identified based on morphology. Then, the in situ signals of stage-matched female to stage-matched male embryos were compared (Figure 5b-f) (see Methods). For each gene, four pairs of female/male samples in average were compared. At HH4, the stage when the microarray samples were prepared, both female and male embryos expressed these genes. The expression domains are largely in the anterior half of the embryo proper and are similar in females and males. However, males exhibited an apparent stronger staining (Figure 5b-f). We also analyzed their expression patterns at HH5 and HH6, when the head process and neural plate begin to take shape. In several of the genes, expression levels increase from HH4 to HH5. The dimorphic expression exists at these stages as well (data not shown). Interestingly, although the spatial patterns of most of the genes are somewhat different, the expression was usually highest in the head process and neural plate (data not shown).

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Stowers Institute for Medical Research, 1000 E, 50th Street, Kansas City, MO 64110, USA.

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.

Show MeSH