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Chicken microchromosomes are hyperacetylated, early replicating, and gene rich
H A McQueen1, G Siriaco, A P Bird
1Institute of Cell and Molecular Biology, University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JR, UK. heather.mcqueen@ed.ac.uk
Genome Research
|July 1, 1998
Summary
Chicken microchromosomes (MICs) are gene-rich, containing approximately 75% of chicken genes. This concentration is supported by histone modifications, CpG island density, and gene mapping data.
Area of Science:
- Avian genetics
- Chromosomal organization
- Molecular biology
Background:
- The chicken karyotype has 39 chromosomes, with 33 classified as microchromosomes (MICs).
- While most mapped chicken genes are on macrochromosomes (MACs), CpG islands (CGIs) are predominantly on MICs.
- CGIs are typically associated with vertebrate genes.
Purpose of the Study:
- To establish that chicken genes are concentrated on MICs using multiple criteria.
- To investigate the distribution of genes and associated elements across chicken chromosome types.
Main Methods:
- Immunocytochemistry to detect acetylated histone H4, a marker for gene presence.
- Detailed analysis of chicken cosmids to assess CpG island-like fragment density.
- Review of published fluorescent in situ hybridization (FISH) mapping data for randomly selected genes.
- Analysis of replication timing during S phase.
Main Results:
- Acetylated histone H4 is highly enriched on MICs.
- CGI-like fragments are approximately six times denser on MICs compared to MACs.
- FISH mapping data shows a significant excess of gene assignments to MICs.
- MICs replicate early in S phase, consistent with gene-rich regions.
- An estimated 75% of chicken genes are predicted to be located on MICs.
Conclusions:
- Chicken microchromosomes (MICs) are gene-rich, contrary to previous gene mapping distributions.
- Multiple lines of evidence, including histone modification, CGI density, and replication timing, support the gene-rich nature of MICs.