Functional Genomics of Silver Foxes
A Microarray Approach to Identify Candidate Genes for Hereditary Hyperplastic Gingivitis
Ranched silver foxes (Vulpes vulpes) in Europe and North America manifest a hereditary overgrowth of the gingival tissue that eventually inhibits normal functioning and presents an animal welfare and economical concern. A similar condition in humans is genetically heterogeneous and maps to at least three different chromosomal regions. Both the human and fox diseases are inherited autosomally; the human inheritance pattern is usually dominant with variable phenotype while the fox condition appears recessive with sex-biased penetrance. To investigate hereditary hyperplastic gingivitis in silver foxes, a three-pronged gene discovery strategy has been launched. First, sequencing and mutational analysis of candidate genes such as SOS1 is underway. The second approach utilizes pedigree-based linkage association analyses to localize the fox mutation to genomic region and identify positional candidate genes. The third strategy, described below, employs microarrays. The three “prongs” of this study are being conducted in a parallel fashion and are intended to complement each other to provide a comprehensive view of the genetic basis of this inherited condition.
DNA microarrays are useful in the present context because they give global transcriptional views of cellular changes in response to disease, development, and environmental factors such as nutrition or infection. Array-based transcript profiling enables the detection of thousands of gene expression patterns simultaneously. A high-density oligonucleotide canine microarray is currently available from Affymetrix - the GeneChip® Canine Genome 2.0 Array enables researchers to simultaneously interrogate 18,000 C. familiaris mRNA/EST-based transcripts and over 20,000 non-redundant predicted genes. By interrogating separate microarrays with cRNA derived from hyperplastic and normal fox gingival tissue we can identify suites of genes that are up- or down-regulated during the expression of hereditary hyperplastic gingivitis. We would predict that the causative gene for HHG is associated with growth control or the cell cycle. SOS1 for example is part of the Ras/MAPK signaling pathway involved in growth and differentiation. Members of signaling cascades activate or repress a wide variety of downstream components, so identification of these components using the canine microarray directs the search backward to the appropriate upstream component. This provides a functional strategy for pinpointing candidate genes.
