Research

Proviral integrations and expression of endogenous Avian leucosis virus during long term selection for high and low body weight in two chicken lines

Sojeong Ka¹ , Susanne Kerje^1,2,4,5 , Lina Bornold¹ , Ulrika Liljegren¹ , Paul B Siegel³ , Leif Andersson^4,5 and Finn Hallböök¹

¹  Department of Neuroscience, Uppsala University, Uppsala, Sweden

²  Department of Medical Sciences, Uppsala University, Uppsala, Sweden

³  Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, USA

⁴  Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden

⁵  Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden

author email corresponding author email

Retrovirology 2009, 6:68doi:10.1186/1742-4690-6-68

Published:	15 July 2009

Abstract

Background

Long-term selection (> 45 generations) for low or high juvenile body weight from a common founder population of White Plymouth Rock chickens has generated two extremely divergent lines, the LWS and HWS lines. In addition to a > 9-fold difference between lines for the selected trait, large behavioural and metabolic differences between the two lines evolved during the course of the selection. We recently compared gene expression in brain tissue from birds representing these lines using a global cDNA array analysis and the results showed multiple but small expression differences in protein coding genes. The main differentially expressed transcripts were endogenous retroviral sequences identified as avian leucosis virus subgroup-E (ALVE).

Results

In this work we confirm the differential ALVE expression and analysed expression and number of proviral integrations in the two parental lines as well as in F₉ individuals from an advanced intercross of the lines. Correlation analysis between expression, proviral integrations and body weight showed that high ALVE levels in the LWS line were inherited and that more ALVE integrations were detected in LWS than HWS birds.

Conclusion

We conclude that only a few of the integrations contribute to the high expression levels seen in the LWS line and that high ALVE expression was significantly correlated with lower body weights for the females but not males. The conserved correlation between high expression and low body weight in females after 9 generations of intercrosses, indicated that ALVE loci conferring high expression directly affects growth or are very closely linked to loci regulating growth.