Bovine horns develop primarily after birth and the presence or absence of horns is due to a single gene. It has been reported that the horn bud appears in the bovine embryo at d 60 of gestation. Our hypothesis is that the gene that determines the presence of horns is expressed in osteoprogenitor cells of the early fetus and will affect the expression of RUNX2, MSX1, MSX2, and/or TWIST1. To test this hypothesis, bovine fetal samples were collected from commercial females at the Caviness Packing Company in Hereford, Texas. Fetuses ranged from d 28 to d 80 of gestation. A survey of the expression of genes from the region on bovine chromosome 1 known to contain the locus that causes horns (IFNAR1 to SOD1), was conducted using qualitative and quantitative RT-PCR, and in situ hybridization. Genes with known roles in osteogenesis and chrondrogenesis (MSX1, TWIST1, RUNX2 and SOX9) were included as positive controls. With the exception of OLIG1, which was only expressed in the brain, all of the genes investigated were expressed in fetal frontal and parietal bones by qualitative RT-PCR. The level of expression of C21orf59, C21orf66, IL10RB, and SFRS15 increased in the frontal bone of horned samples from d 55 to d 70 of gestation. At d 60 of gestation, a change in the shape of the frontal bone was observed, which has been reported to be the developmental stage when the horn bud appears. At this time point, MSX1, TWIST1, RUNX2 and SOX9 were detected in frontal bone, in cells from the osteoblast lineage, as expected. Furthermore, C21orf59, C21orf62, C21or66 and SFRS15 from the polled interval were localized to developing mesenchyme, osteoblasts and/or osteoclasts of the frontal bone, suggesting that each of these genes has a role in intramembranous bone formation. In addition, gradients of expressed C21orf66 and SFRS15 were detected in developing endochondral bone. There was evidence of an antisense transcript of C21orf66 expressed in the same cell types as the sense transcript. Further characterization of this antisense transcript demonstrated that it covered the entire sense transcript. Based on observed expression in the mesenchyme, rather than just in mature osteoblasts or osteoclasts, C21orf66 and/or its antisense transcript become the most likely candidates for the polled locus.

The horned condition in cattle is believed to be the wild type with morphogenesis primarily occurring after birth. The polled condition has existed since domestication and has been selected for its economic importance. The polled locus has previously been mapped by genetic linkage analysis to the proximal region of bovine chromosome 1. In order to help us eventually identify the causative mutation, the objective of the study was to structurally and functionally characterize the polled interval from IFNAR1 to SOD1 on BTA1. Our hypothesis was that the polled locus is a tissue specific transcription factor that is expressed in the developing horn buds and acts directly or indirectly upon SOX9. A 2.5 Mb BAC contig and STS content map of the polled interval was constructed. Three candidate genes encoding transcription factors were identified within this region but only C21orf66 was expressed in the horn buds from 1 d old Bos indicus influenced calves. The C21orf66 gene has 18 exons, spans 30,976 bp of genomic DNA, and 144 SNP were identified. No single SNP discovered in C21orf66 can be attributed as the causative mutation. None of the genes from the polled interval were differentially expressed in skin and horn from 1 d old Bos indicus influenced calves. However, there were significant differences in the levels of expression of RUNX2, SOX9, BMP4, PRKCA, and FOXL2 in these samples. Expression of RUNX2 was localized to the osteoblasts, and both RUNX2 and SOX9 were expressed in sebaceous glands of the horn at 1 d of age. Histological examination of horns and scurs from newborn, 5 to 6 mo, and ~1.5 yr old Bos indicus influenced cattle suggest that horns form through intramembranous ossification. Based on the data presented herein, we propose that the polled locus is upstream of RUNX2 and SOX9 in the osteogenic pathway, and could have its primary effect on the differentiation of mesenchymal condensations. The genes IL10RB, SFRS15, C21orf66, OLIG1, OLIG2 and HUNK remain candidates for the polled locus and warrant further investigation.

This research investigates alternate methods of implementing a redundant communications ring for polled network applications. FDDI and a unique solution (the tone method) designed specifically for this application are compared. In polled networks one of the most critical parameters is the time required to interrogate all of the nodes in the network. This parameter, called the poll time, is compared for the two solutions under various operating conditions, including the instances when the ring is intact and when the ring has experienced a failure, causing it to operate in the redundant mode. As expected, the solution designed specifically for this application performed better than FDDI. The tone method, which requires very little overhead and is not limited by distance or number of nodes, is described in detail, as are the results of poll time comparisons. / Master of Science