Christine A. Rees

Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog

Merle is a pattern of coloring observed in the coat of the domestic dog and is characterized by patches of diluted pigment. This trait is inherited in an autosomal, incompletely dominant fashion. Dogs heterozygous or homozygous for the merle locus exhibit a wide range of auditory and ophthalmologic abnormalities, which are similar to those observed for the human auditory–pigmentation disorder Waardenburg syndrome. Mutations in at least five genes have been identified as causative for Waardenburg syndrome; however, the genetic bases for all cases have not been determined. Linkage disequilibrium was identified for a microsatellite marker with the merle phenotype in the Shetland Sheepdog. The marker is located in a region of CFA10 that exhibits conservation of synteny with HSA12q13. This region of the human genome contains SILV, a gene important in mammalian pigmentation. Therefore, this gene was evaluated as a candidate for merle patterning. A short interspersed element insertion at the boundary of intron 10/exon 11 was found, and this insertion segregates with the merle phenotype in multiple breeds. Another finding was deletions within the oligo(dA)-rich tail of the short interspersed element. Such deletions permit normal pigmentation. These data show that SILV is responsible for merle patterning and is associated with impaired function of the auditory and ophthalmologic systems. Although the mutant phenotype of SILV in the human is unknown, these results make it an intriguing candidate gene for human auditory–pigmentation disorders.

Analysis of gene transcript profiling and immunobiology in Shetland sheepdogs with dermatomyositis

Dermatomyositis (DM) is a canine and human inflammatory disease of the skin and muscle that is thought to be autoimmune in nature. In dogs, DM occurs most often in the rough collie and Shetland sheepdog. Characteristic skin lesions typically develop on the face, ears, tail, and distal extremities. The severity of lesions varies and is thought to increase with stressful stimuli. Previous studies in the collie suggest that DM is inherited in an autosomal dominant fashion with incomplete penetrance. The work presented here concerns gene transcripts profiling and immunobiology of DM in the Shetland sheepdog. Gene transcript profiles were generated for affected and normal skin using a canine-specific oligonucleotide array having 49,929 probe sets. Two-hundred and eight-five gene transcripts, many of which are involved in immune function, were found to be differentially regulated in these tissues. Also reported are Western blot, immunohistochemistry, and immunofluorescence analyses which showed that staining patterns with sera from normal and affected dogs are quite similar. While our work suggests that canine DM is a disease that may be immune mediated, it did not detect the production of specific disease-associated autoantibodies.

Canine SINEs and Their Effects on Phenotypes of the Domestic Dog

Short interspersed elements (SINEs) are mobile elements that contribute to genomic diversity through the addition of genetic material. Recent genomic analyses have vastly augmented our knowledge of both human- and canine-specific SINEs. SINEC_Cf is a major SINE of the canid family that has undergone recent expansion and is thought to be present in half of all genes. To date, only three phenotypes of the domestic dog have been attributed to a SINE. One of these is merle, a coat pattern characterized by patches of full color on a diluted background and associated with ocular and auditory anomalies. A SINEC_Cf in the SILV gene causes merle patterning by altering the cDNA transcript and has unique characteristics that are likely responsible for the random nature of the phenotype.

Skin surface lipids and skin and hair coat condition in dogs fed increased total fat diets containing polyunsaturated fatty acids

It is generally believed that diets containing increased amounts of polyunsaturated fatty acids (PUFA) result in improved canine skin and hair coat (SHC). However, the extent to which dietary fat amount and type play a role remains to be systematically investigated. The objective of this study was to investigate the role of both increased dietary fat amount and type on SHC assessments of dogs. Improvements of SHC conditions were investigated after feeding three diets containing increased total dietary fat (i.e. 13% total fat) for 12 weeks in relation to a lower fat acclimation diet (i.e. 9% total fat). The higher fat diets varied in polyunsaturated and saturated fat types and amounts but total fat was kept constant. Skin and hair coat assessments were performed at selected intervals by a trained group of veterinarians and graduate students. In addition, hair lipids were fractionated by thin layer chromatography after extraction of plucked hair samples. Significant improvements were found in hair coat glossiness and softness in all dogs fed the higher fat diets in relation to the acclimation diet. Improvements as a result of fat type were also seen but only at 12 weeks. A parallel finding was a marked increase in hair cholesteryl ester content determined at the end of the study at which time SHC scores were significantly improved. Skin and hair coat condition improvements may thus be related to increased cholesteryl ester deposited on the hair shaft surface when high fat diets are fed. Whereas this finding is preliminary, hair lipid analysis may be a useful, non-invasive technique with which to help assess dietary effects on canine SHC.

New Drugs in Veterinary Dermatology

This article discusses several different new drugs currently being used in dermatology. Most of the drugs discussed showed some promise as being a useful therapy in veterinary medicine, but a few have questionable efficacy (nonsedating antihistamines). The majority of these drugs have not had any pharmacokinetic or clinical trials conducted on them in small animals. Hopefully, in the future, more studies are funded so that we can determine the clinical therapeutical efficacy and appropriate doses for these drugs.