175 TRANSCRIPTOME ANALYSIS OF BOVINE DAY 150 FETAL LIVER AND COTYLEDON REVEALS GENES INVOLVED IN FETAL GROWTH

Abstract

Major problems in breeding of modern dairy cows include increasing rates of stillbirth and dystocia, associated with elevated costs for veterinary intervention (caesarean section) and loss of production animals (cows and calves). Rates of stillbirth as high as 12% have been reported, primarily caused by fetal overgrowth and increased birth weight. In order to discover molecular markers for selection against stillbirth, we developed a model for the inheritance of fetal growth traits. A Fleckvieh bull segregating for paternal stillbirth was used for insemination of 36 cows that were slaughtered at Day 150 of pregnancy in order to recover and phenotype the fetuses. The mode of inheritance indicated involvement of imprinting. Mapping results suggested an imprinted region on chromosome 9 as candidate for the stillbirth QTL. Due to the complexity of the trait, we opted for a holistic approach that is not restricted to the QTL candidate region but allows identification of genes and networks that influence fetal growth. Transcriptome profiles of liver and cotyledon samples from the fetuses with the highest (n = 10) and the lowest total weight n = 10) were analyzed using Affymetrix Bovine GeneChips (Affymetrix, Inc., Santa Clara, CA, USA). Analysis with the program SAM showed 41 up- and 4 down-regulated genes in liver samples of the heavy-weight group. Most of these genes are involved in immune response. Interestingly, many of these genes are reported to be regulated by vitamin D. Furthermore, vitamin D is closely connected to the IGF1 system and thus the most important fetal growth regulation circuit. Seasonal effects on vitamin D levels could mostly be excluded by the experimental design and did not correlate with growth traits. Most likely, the mRNA levels of our candidate genes were influenced by alterations in the IGF1/vitamin D circuit and did not cause the observed weight differences. The imprinted candidate genes showed no correlation with fetal weight. Gene set enrichment analysis indicated enhanced metabolic activity in the liver of heavy-weight fetuses. Genes from the QTL region showed a clear enrichment in correlation with fetal weight, confirming their involvement in fetal growth. The gene with the best correlation, GHITM (growth hormone inducible transmembrane protein), could give an explanation for the enhanced metabolic activity, as it is reported to function as a metabolic regulator. Simultaneous analysis of the data sets for liver and placenta in a linear model (R-package LIMMA; Smyth 2004 Stat. Applic. Genet. Mol. Biol. 3, art. 3) yielded essentially the same differentially expressed genes for liver and a higher number of differentially expressed genes for placenta (89 up- and 114 down-regulated), with little overlap between the two tissues.

This work was supported by Grant BMBF FUGATO-Fertilink.