Dwarfism is an undesirable phenotype in beef cattle that has reduced profitability for both commercial and pure bred producers since the 1950.s. In 2002, a flare up of dwarfism on several ranches across the US led to new genomic research designed to find the genetic mutation. Linkage-mapping of Bos taurus autosome 6 (BTA6) indicated a LOD score of 7.34 between microsatellite markers AFR227 and BM4311. To expedite the fine-mapping process, the BLAST Extension and Alignment Program "BEAP" was developed to assist with sequence assembly of the Angus dwarfism locus prior to completion of the bovine genome project. Four positional candidate genes, bone morphogenetic protein (BMP) 2 kinase, bone morphogenetic protein (BMP) 3, fibroblast growth factor 5, and cGMP-dependant, type II, protein kinase (PRKG2 ), were re-sequenced using BEAP output as template. Within PRKG2, a C/T nonsense mutation was discovered (R678Z) that truncates PRKG2 by 85 amino acids (AA), including 25 AA of the kinase domain. A mouse knockout model and naturally occurring PRKG2 mutants demonstrate that lack of PRKG2 function causes dwarfism. Recent work in the rat indicates that PRKG2 signals SOX9 to regulate the transition from proliferative to hypertrophic growth in the growth plate. Gene expression data in the rat demonstrated that PRKG2 mutants lose the ability to regulate SOX9 mediated collagen (Col) 2 and Col10 transcription. To determine if the Angus R678Z PRKG2 mutation altered collagen expression, wild-type and R678Z bovine vectors were assayed in a cell culture transfection experiment. Real-time PCR results confirmed that COL2 was inappropriately over-expressed in cells transfected with the R678Z mutation as compared to cells transfected with wild-type PRKG2 (p<0.01). Over-expression of COL2 in dwarf cattle was confirmed by real-time PCR of dwarf and normal cattle growth plate tissue samples (p<0.0001). Expression of COL10 was found to be upregulated in dwarf animals as well (p=0.05). These experiments indicate that the R678Z mutation is a functional mutation, resulting in a loss of PRKG2 regulation of COL2 and COL10 mRNA expression. To determine if the R678Z marker was an accurate predictor of Angus dwarfism, we conducted a breeding experiment. Six calves were produced by embryo transfer and their phenotype was predicted with 100% accuracy prior to expression of the phenotype. Four animals were predicted to be dwarves, homozygous for the R678Z PRKG2 marker, and two were predicted to be normal, heterozygous for the R678Z PRKG2 marker. Differences in skeletal growth were characterized by measurements of gross differences in height, long bone and vertebral column length. Animals homozygous for the R678Z PRKG2 marker had shorter metatarsals (reduced 4.5cm; p<0.01), and fused ulna/radius (reduced 7.5cm; p<0.01) bones. No significant differences were observed between these animals for head length, calvarium (skull) width, or bone circumference (p>0.25). Stature and body length were also compared between animals homozygous for the R678Z PRKG2 marker and the R678Z PRKG2 heterozygotes at approximately 210 days of age. Animals homozygous for the R678Z PRKG2 marker were 15.8cm shorter (p<0.0001) and had spinal lengths reduced by 20.7 cm (p<0.0001) (data not shown). Transcriptional profiling of the null PRKG2 dwarf versus wild-type animals was performed using a 70 mer cDNA microarray to assess global changes in gene expression. Both COL2 and COL10 were found to be differentially expressed in the same direction and similar magnitude as observed by real-time PCR (p<0.05). In addition, non-sense mediated decay of dwarf PRKG2 and up regulation of Wnt5a, and collagen9, markers of proliferation, was observed (p<0.05). Multiple genes were found to be differentially expressed in the MAPK and Wnt5a signaling cascades. In addition, many Golgi transport and neuronally expressed genes were observed as differentially expressed. These genes provide interesting candidates for understanding the intermediate processes in the PRKG2 intracellular signaling pathway that regulate proliferation and developmental timing of the growth plate. Implications of these discoveries will allow Angus breeders to eliminate dwarfism and present a model to study PRKG2 function in the growth plate.