Long-term genetic selection reduced prevalence of hip and elbow dysplasia in 60 dog breeds

Canine hip dysplasia (CHD) and elbow dysplasia (ED) impact the health and welfare of all dogs. The first formally organized assessment scheme to improve canine health centered on reducing the prevalence of these orthopedic disorders. Phenotypic screening of joint conformation remains the currently available strategy for breeders to make selection decisions. The present study evaluated the efficacy of employing phenotypic selection on breed improvement of hips and elbows using the Orthopedic Foundation for Animals complete database spanning the 1970–2015 time period. Sixty breeds having more than 1000 unique hip evaluations and 500 elbow evaluations (1,056,852 and 275,129 hip and elbow records, respectively) were interrogated to derive phenotypic improvement, sex and age at time of assessment effects, correlation between the two joints, heritability estimates, estimated breeding values (EBV), and effectiveness of maternal/paternal selection. The data demonstrated that there has been overall improvement in hip and elbow conformation with a reduction in EBV for disease liability, although the breeds differed in the magnitude of the response to selection. Heritabilities also differed substantially across the breeds as did the correlation of the joints; in the absence of a universal association of these differences with breed size, popularity, or participation in screening, it appears that the breeds themselves vary in genetic control. There was subtle, though again breed specific, impact of sex and older ages on CHD and ED. There was greater paternal impact on a reduction of CHD. In the absence of direct genetic tests for either of these two diseases, phenotypic selection has proven to be effective. Furthermore, the data underscore that selection schemes must be breed specific and that it is likely the genetic profiles will be unique across the breeds for these two conditions. Despite the advances achieved with phenotypic selection, incorporation of EBVs into selection schemes should accelerate advances in hip and elbow improvement.

Ten inherited disorders in purebred dogs by functional breed groupings

Background

Analysis of 88,635 dogs seen at the University of California, Davis Veterinary Medical Teaching Hospital from 1995 to 2010 identified ten inherited conditions having greater prevalence within the purebred dog population as compared to the mixed-breed dog population: aortic stenosis, atopy/allergic dermatitis, gastric dilatation volvulus (GDV), early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, hypothyroidism, intervertebral disk disease (IVDD), and hepatic portosystemic shunt. The objective of the present study was to ascertain if disorders with higher prevalence in purebreds were restricted to particular breed group classifications within the purebred population, specifically the American Kennel Club breed grouping or groups with genomic similarities based upon allele sharing. For each disorder, healthy controls seen at the hospital during that same time period were matched for age, weight, and sex to each affected dog to determine risk of disease presentation in the purebred group as compared to that of the mixed-breed population. To enhance reliability of the analyses, sampling of matched healthy to affected dogs was repeated 50 times. For each comparison, the purebred subgroups to mixed-breed odds ratio was determined as was the mean P value used to test this ratio.

Results

For aortic stenosis, GDV, early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, and portosystemic shunt, most purebred groups were not statistically distinct from the mixed-breed population with higher prevalence in purebreds restricted to distinct subsets of purebred dogs. The conditions of atopy/allergic dermatitis, hypothyroidism, and IVDD were more pervasive across the purebred population with many groups having higher prevalence than the mixed-breed population. The prevalence of IVDD in purebred terrier groups was statistically lower than that observed for mixed-breed dogs.

Conclusions

The results offer an assessment of the distribution of inherited disorders within purebred dogs and illustrate how mixed-breed and subpopulations of purebred dogs do not differ statistically in prevalence for certain disorders. Some disorders appear linked to common ancestors providing insight into disease allele origin whereas others may be due to selection for common structural morphology. Knowledge of the origin of a condition may aid in reducing its prevalence in the dog population as a whole.

Electronic supplementary material

The online version of this article (doi:10.1186/s40575-015-0021-x) contains supplementary material, which is available to authorized users.

The Regulation of IGF-1 Gene Transcription and Splicing during Development and Aging

It is commonly known that the insulin-like growth factor-I gene contains six exons that can be differentially spliced to create multiple transcript variants. Further, there are two mutually exclusive leader exons each having multiple promoter sites that are variably used. The mature IGF-I protein derived from the multiplicity of transcripts does not differ suggesting a regulatory role for the various transcript isoforms. The variant forms possess different stabilities, binding partners, and activity indicating a pivotal role for the isoforms. Research has demonstrated differential expression of the IGF-I mRNA transcripts in response to steroids, growth hormone, and developmental cues. Many studies of different tissues have focused on assessing the presence, or putative action, of the transcript isoforms with little consideration of the transcriptional mechanisms that generate the variants or the translational use of the transcript isoforms. Control points for the latter include epigenetic regulation of splicing and promoter usage in response to development or injury, RNA binding proteins and microRNA effects on transcript stability, and preferential use of two leader exons by GH and other hormones. This review will detail the current knowledge of the mechanical, hormonal, and developmental stimuli regulating IGF-1 promoter usage and splicing machinery used to create the variants.

Determining the heritable component of dairy cattle foot lesions

Lameness and hoof health affect dairy cows as an animal welfare issue, in decreased milk production, and in premature culling. Selection schemes for dairy cattle focus on sire contribution to milk production, with little consideration of the cow's physical structure or disease probability. On 3 commercial California dairies, 6 phenotypic binary hoof traits that contribute to lameness were recorded: white line disease, sole ulcer, other claw horn lesions, foot rot (interdigital phlegmon), foot warts (digital dermatitis), and other lesions. Monthly lactation records were collected from December 2006 to April 2009 with weekly observations of hoof lesions for lame and dry cows. In addition to hoof lesion information, data on cows (n=5,043) included parentage, birth date, freshening date, lactation number, and date of lameness diagnosis. The prevalence of hoof lesions ranged from a low of 2.2% (foot rot) to a high of 17.1% (foot warts). The farm environment increased the odds ratio depending upon the lesion. Lameness was more common in early lactation and as lactation number increased. Using a threshold model, heritabilities and repeatabilities were estimated for each binary trait. The heritability for risk varied by lesion, with the higher estimates being 0.40 (95% confidence interval: 0.20-0.67) for digital dermatitis and 0.30 (95% confidence interval: 0.08-0.63) for sole ulcer. Including terms to account for cow productivity on either a 305-d mature-equivalent basis or a per-lactation basis had minimal effect on the heritability estimates, suggesting that selection for hoof health is not correlated with response to selection for greater milk production and that improvement could be made for both traits. The genetic component lends support for further genetic studies to identify loci contributing to some of the lesion phenotypes such as foot warts or sole ulcers, 2 of the top 3 causes of lameness in dairy cattle.

Growth hormone enhances arachidonic acid metabolites in a growth hormone transgenic mouse

In a transgenic growth hormone (GH) mouse model, highly elevated GH increases overall growth and decreases adipose depots while low or moderate circulating GH enhances adipose deposition with differential effects on body growth. Using this model, the effects of low, moderate, and high chronic GH on fatty acid composition were determined for adipose and hepatic tissue and the metabolites of 20:4n-6 (arachidonic acid) were characterized to identify metabolic targets of action of elevated GH. The products of Δ-9 desaturase in hepatic, but not adipose, tissue were reduced in response to elevated GH. Proportional to the level of circulating GH, the products of Δ-5 and Δ-6 were increased in both adipose and hepatic tissue for the omega-6 lipids (e.g., 20:4n-6), while only the hepatic tissues showed an increase for omega-3 lipids (e.g., 22:6n-3). The eicosanoids, PGE₂ and 12-HETE, were elevated with high GH but circulating thromboxane was not. Hepatic PTGS1 and 2 (COX1 and COX 2), SOD1, and FADS2 (Δ-6 desaturase) mRNAs were increased with elevated GH while FAS mRNA was reduced; SCD1 (stearoyl-coenzyme A desaturase) and SCD2 mRNA did not significantly differ. The present study showed that GH influences the net flux through various aspects of lipid metabolism and especially the desaturase metabolic processes. The combination of altered metabolism and tissue specificity suggest that the regulation of membrane composition and its effects on signaling pathways, including the production and actions of eicosanoids, can be mediated by the GH regulatory axis.

Certification testing as an acute naturalistic stressor for disaster dog handlers

USA Federal Disaster Canine Teams, consisting of a handler and a dog, are essential for locating survivors following a disaster. Certification, required by the Federal Emergency Management Agency Urban Search and Rescue organization, requires two successful mock searches. Confirmation of the certification testing process as an acute stressor might offer further opportunities to consider stress effects on handlers and dogs in a controlled environment. This study used a pretest-posttest design to evaluate relationships between salivary hormone concentrations (cortisol and testosterone) and subjective stress ratings in handlers and controls, handler assessments of stress in their dogs, and posttest temperature and pulse rate in dogs. Posttest, both subjective stress ratings and salivary cortisol concentration were higher in handlers than controls with both correlated to handlers' assessment of stress in their dogs. Handlers' posttest salivary cortisol concentration was associated with posttest dog pulse and temperature. Posttest cortisol concentration was lower in handlers who were successfully certified compared with those who failed, and was also lower in handlers whose primary occupation was "firefighter". Salivary testosterone concentrations increased from pretest to posttest in handlers but decreased in controls, and higher posttest handler testosterone concentration was negatively associated with posttest dog pulse rate. These findings confirm certification testing as an acute stressor, suggest a relationship between stress and performance moderated by occupation, and demonstrate an interaction between handler stress and dog physiological responses. This certification testing offers a controlled environment for targeted evaluation of effects of an acute naturalistic stressor on disaster dog handlers and dogs.

Biological markers of neonatal calf performance: the relationship of insulin-like growth factor-I, zinc, and copper to poor neonatal growth

Raising a heifer calf to reproductive age represents an enormous cost to the producer. Poor neonatal growth exacerbates the costs incurred for rearing, and use of blood variables that may be associated with poorly growing calves may offer predictive value for growth and performance. Thus, the principal objective of the present study was to describe changes in serum IGF-I, zinc, and copper from birth to 90 d in Holstein calves, while accounting for sex and twin status, in poorly growing calves and calves growing well. A second objective was to test the hypothesis that an association exists between these serum variables and morphometric indicators of growth. Measurements of BW, length, and height were recorded at birth and at 30, 60, and 90 d of age. Jugular blood (12 mL) was collected from each calf on d 1 to determine serum total protein, serum IgG, packed cell volume, serum zinc, serum copper, serum IGF-I, and CD18 genotype for bovine leukocyte adhesion deficiency; serum zinc, serum copper, and serum IGF-I (predictor variables) were also determined for each calf on d 2 through 10 and on d 30, 60, and 90. Stepwise multiple regression and logistic regression analyses were used to examine the relationships between the predictor variables and the dependent variables (BW, height, and length at d 30, 60, and 90 of life). Birth weight, sex, serum IGF-I (at all ages), serum copper, and the serum copper-to-zinc ratio were associated, to varying degrees, with the dependent growth variables. Birth weight was consistently the dominant predictor. In conclusion, these results suggest that lighter birth weight, reduced serum IGF-I, and inflammation may be important causes of poor growth in neonatal Holstein dairy calves.

Pamidronate alters the growth plate in the oim mouse model for osteogenesis imperfecta

Bisphosphonates alleviate bone pain and fractures associated with osteogenesis imperfecta (OI). Using the oim mouse model to simulate variations in OI severity, the effect of pamidronate on bone growth was assessed. Homozygous (oim/oim) and heterozygous (oim/wt) mice from 4 to 12 weeks of age were given pamidronate at 0 mg/kg/wk (control), 1.25 mg/kg/wk (low) and 2.5 mg/kg/wk (high). Humerus and ulna lengths were reduced in oim/oim mice relative to those of the oim/wt. Further, the oim/oim genotype exhibited a 23.5% prevalence of fractures in these bones as compared to the 2.8% prevalence observed in the oim/wt mice. Pamidronate tended to reduce fracture prevalence in a dose dependent manner for the oim/oim genotype (p<0.08) but had no effect on the low fracture prevalence in oim/wtmice. The high dose of pamidronate reduced bone length in females of both genotypes but not males when compared to control (p<0.01). Pamidronate increased growth plate area (p<0.05) by increasing growth plate height, particularly the proliferative and hypertrophic zones, in both genotypes indicating reduced growth plate cell turnover. The increased area coincided with increased osteoclast numbers in the metaphyseal region (p<0.05) though when corrected for the greater mineralized surface area that accompanies bisphosphonate treatment, osteoclasts per surface area were reduced indicating reduced resorptive capacity. This study demonstrated that the effects of pamidronate were independent of the degree of collagen deficit and fracture prevalence was improved in the most severe OI model, the oim/oim genotype.

Alendronate inhibits VEGF expression in growth plate chondrocytes by acting on the mevalonate pathway

Bisphosphonates decrease chondrocyte turnover at the growth plate and impact bone growth. Likewise vascular endothelial growth factor (VEGF) plays an important role in endochondral bone elongation by influencing chondrocyte turnover at the growth plate. To investigate whether the action of bisphosphonate on the growth plate works through VEGF, VEGF protein expression and isoform transcription in endochondral chondrocytes isolated from growing mice and treated with a clinically used bisphosphonate, alendronate, were assessed. Alendronate at 10µM and 100µM concentrations decreased secreted VEGF protein expression but not cell associated protein. Bisphosphonates are known to inhibit the mevalonate intracellular signaling pathway used by VEGF. Addition of the mevalonate pathway intermediates farnesol (FOH) and geranylgeraniol (GGOH) interacted with the low concentration of alendronate to further decrease secreted VEGF protein whereas FOH partially restored VEGF protein secretion when combined with the high alendronate. Similar to the protein data, the addition of alendronate decreased VEGF mRNA isoforms. VEGF mRNA levels were rescued by the GGOH mevalonate pathway intermediate at the low alendronate dose whereas neither intermediate consistently restored the VEGF mRNA levels at the high alendronate dose. Thus, the bisphophonate alendronate impairs growth plate chondrocyte turnover by down-regulating the secreted forms of VEGF mRNA and protein by inhibiting the mevalonate pathway.

Bisphosphonate treatment in the oim mouse model alters bone modeling during growth

Osteogenesis imperfecta (OI) is a heritable disease, which results from an abnormal amount or structure of Type I collagen. Bisphosphonates, a class of synthetic antiresorptive drugs, used in osteoporosis management, are also used to decrease fracture incidence and improve quality of life in children with OI. In this study, we used the oim mouse to test the hypotheses that pamidronate treatment during active growth (1) produces larger, stronger, stiffer long bone diaphyses without altering bone material properties, and (2) negatively impacts longitudinal bone growth. Our results indicate that femoral cross-sectional moment of inertia in the distal metaphysis tended to increase with pamidronate treatment and that the treated bones are thicker and structurally stiffer, but shorter than their control-dose counterparts.

Long Term Cyclic Pamidronate Reduces Bone Growth by Inhibiting Osteoclast Mediated Cartilage-to-Bone Turnover in the Mouse

Bisphosphonates, used to treat diseases exhibiting increased osteoclast activity, reduce longitudinal bone growth through an as yet undefined mechanism. Pamidronate, an aminobisphosphonate, was given weekly to mice at 0, 1.25, or 2.50 mg/kg/wk beginning at 4 weeks of age. At 12 weeks of age, humeral length, growth plate area, regional chondrocyte cell numbers, chondrocyte apoptosis, TRAP stained osteoclast number, and osteoclast function assessed by cathepsin K immunohistochemistry were quantified. Humeral length was decreased in pamidronate treated mice compared to vehicle control mice, and correlated with greater growth plate areas reflecting greater proliferative and hypertrophic chondrocyte cell numbers with fewer hypertrophic cells undergoing apoptosis. Pamidronate treatment increased TRAP stained osteoclast numbers yet decreased cathepsin K indicating that pamidronate repressed osteoclast maturation and function. The data suggest that long term cyclic pamidronate treatment impairs bone growth by inhibition of osteoclast maturation thereby reducing cartilage-to-bone turnover within the growth plate.

Enhanced skeletal growth of sheep heterozygous for an inactivated fibroblast growth factor receptor 3

Normal fibroblast growth factor receptor 3 (FGFR3) acts as a negative bone growth regulator by restricting chondrocyte proliferation and endochondral bone elongation. In sheep, a heritable mutation that inactivates FGFR3 produces skeletal overgrowth when homozygous, this condition is commonly referred to as spider lamb syndrome (SLS). We hypothesized that sheep heterozygous for the inactivated FGFR3 mutation (FGFR3(SLS/+)) would exhibit enhanced long bone growth and greater frame size; additionally, the isolated effects of increased bone growth would translate into greater BW and larger LM area relative to normal lambs at harvest. The current study investigated bone length and LM area of FGFR3(SLS/+) sheep at maturity and during growth. At maturity, FGFR3(SLS/+) ewes exhibited a larger frame size and longer bones than normal FGFR3(+/+) ewes (P < 0.05). Similarly, FGFR3(SLS/+) lambs had greater frame sizes than normal FGFR3(+/+) lambs, as indicated by increased metacarpal III length and height at withers (P < 0.05). The FGFR3(SLS/+) lambs took longer than the normal FGFR3(+/+) lambs to reach the 60-kg common BW harvest end point (P < 0.05). The FGFR3(SLS/+) lambs showed no difference in BW, ADG, or LM area at any age compared with normal FGFR3(+/+) lambs (P > 0.2). A similar LM area produced in the context of a greater frame size and skeletal length produces a greater muscle volume, thereby potentially increasing meat yield. The results of this study suggest that FGFR3(SLS/+) animals exhibit a relaxation of the normal inhibition of chondrocyte proliferation, resulting in an increase in the overall frame size. The sheep industry could utilize the naturally occurring genetic mutation in FGFR3 to potentially increase meat yields with enhanced skeletal growth as an alternative to exogenous growth promotants.

Genetic evaluation of Addison's disease in the Portuguese Water Dog

BACKGROUND

Addison's disease, also known as hypoadrenocorticism, has been reported in many individual dogs, although some breeds exhibit a greater incidence than the population as a whole. Addison's is presumed to be an autoimmune mediated hereditary defect but the mode of inheritance remains unclear. In particular, the heritability and mode of inheritance have not been defined for the Portuguese Water Dog although Addison's is known to be prevalent in the breed.

RESULTS

The analyses present clear evidence that establishes Addison's disease as an inherited disorder in the Portuguese Water Dog with an estimate of heritability of 0.49 (+/- 0.16); there were no differences in risk for disease across sexes (p > 0.49). Further, the complex segregation analysis provides suggestive evidence that Addison's disease in the Portuguese Water Dog is inherited under the control of a single, autosomal recessive locus.

CONCLUSION

The high heritability and mode of inheritance of Addison's disease in the Portuguese Water Dog should enable the detection of segregating markers in a genome-wide scan and the identification of a locus linked to Addison's. Though the confirmation of Addison's disease as an autosomal recessive disorder must wait until the gene is identified, breeders of these dogs may wish to keep the present findings in mind as they plan their breeding programs to select against producing affected dogs.

Transgene transmission to progeny by oMt1a-oGH transgenic mice

Most studies utilizing transgenic technology focus on the impact to traits of interest, rather than propagation of the transgene to offspring. In animals containing growth hormone constructs, transgene transmission to progeny follows a Mendelian pattern of inheritance in the first few generations following generation of a founder animal, but decreases in subsequent generations. In the present study, the ovine metallothionein 1a-ovine growth hormone (oMt1a-oGH) transgenic mouse was used to determine whether transgene transmission rate to progeny was affected by overexpression of ovine growth hormone in the transgenic parent. The oMt1a-oGH mouse is a useful model for assessing transgene transmission, as the construct is easily regulatable and transgene inactivation results in a return of plasma GH to basal levels. Male and female hemizygous oMt1a-oGH mice were assigned to 1 of 3 treatment groups: (1) mice never actively expressing the transgene, (2) mice actively expressing the transgene from 3 weeks of age, and (3) mice actively expressing the transgene from 3 to 11 (males) or 3 to 8 (females) weeks of age. Transgenic mice were mated to wild type animals and the resulting progeny were genotyped. Males never actively expressing the transgene passed on the transgene to progeny in a Mendelian fashion, while males actively expressing the transgene transmitted the transgene to a smaller than expected number of progeny. However, following inactivation of the oMt1a-oGH construct in transgenic males, subsequent offspring demonstrated Mendelian inheritance of the transgene. In contrast, females expressing the transgene from 3 to 8 weeks of age were able to pass on the oMt1a-oGH construct in a Mendelian fashion, but females from other treatment groups were not. In oMt1a-oGH males, reduced transgene transmission appears to be due to selection against transgenic gametes. In females, however, selection against the transgenic genotype likely occurs at the embryonic level.

Spatial distribution of growth hormone receptor, insulin-like growth factor-I receptor and apoptotic chondrocytes during growth plate development

Linear bone growth depends upon proliferation, maturation, and apoptosis of growth plate chondrocytes, processes regulated by growth hormone (GH) and insulin-like growth factor-I (IGF-I). To investigate the contribution of GH, IGF-I and apoptosis to growth plate function, the expression of GH receptor (GHR) and IGF-I receptor (IGF-IR) mRNA were evaluated by in situ hybridization in fractionated costochondral growth plates of growing rats (at 2, 4, and 7 weeks). Apoptosis was determined by TUNEL assay and morphology in histological sections. GHR mRNA was greatest in resting cells with hypertropic cells increasing GHR expression with increasing age. Hypertropic and resting cell IGF-IR mRNA declined over the ages studied. Receptor mRNA expression was altered by exposing cells to GH or IGF-I. GH and IGF significantly decreased GHR mRNA in proliferative cells. GH and IGF also decreased IGF-IR mRNA in resting cells and the 2- and 4-week-old proliferative and hypertropic cells. Treating cells in culture with GH increased the number of apoptotic cells across all ages and zones. Histologically, apoptotic cells were observed at the chondro-osseous junction and within actively proliferating chondrocytes but not in resting cells. Apoptosis was highest at 4 weeks of age with lateral regions displaying the greatest number of cells undergoing apoptosis. These data indicate that apoptosis plays a role in growth plate function, particularly spatial configuration as indicated by the preferential lateral cell apoptosis. The susceptibility of proliferative cells to GHR and IGF-IR down regulation during the period of greatest apoptosis supports a role for the GH-IGF axis in both proliferation and apoptosis during growth plate development.

Leptin modulates fertility under the influence of elevated growth hormone as modeled in oMt1a-oGH transgenic mice

Elevated growth hormone (GH) concentrations suppress reproductive function in a variety of species, although it is unclear whether GH directly suppresses reproductive performance, or whether GH activates other pathways to achieve these effects. The ovine metallothionein 1a-ovine GH (oMt1a-oGH) transgenic mouse has been used to model the effects of GH on both body composition and reproductive function. A recent report has documented increased leptin levels in obese oMt1a-oGH mice. Given the importance of leptin in modulation of the reproductive endocrine axis, as well as the reports documenting reduced leptin signal transduction in animals with elevated leptin levels, we hypothesized that high leptin concentrations in response to elevated GH would reduce fertility. To determine the effects of high circulating leptin levels on the reproductive endocrine axis, we assessed hypothalamic neuropeptide Y (NPY) and GnRH expression. At weaning, oMt1a-oGH transgenic (TG) and wild-type (WT) female mice were allocated to one of four treatment groups: oMt1a-oGH females chronically expressing the transgene (TG ON); oMt1a-oGH females expressing the transgene from 3 to 8 weeks of age (TG ON/OFF); WT females receiving the transgene stimulus from 3 to 8 weeks of age (WT ON/OFF); and WT females never receiving the transgene stimulus (WT OFF). Eight-week-old females were housed with males for a 2-week period, after which females were isolated from males and allowed to carry pregnancies to term. Body and gonadal fat pad (GFP) weights, along with plasma leptin concentrations, estrous cyclicity, pregnancy rate and litter characteristics, were recorded for each female. Chronic expression of the oMt1a-oGH transgene resulted in larger leaner mice, and inactivation of the transgene produced obese females. Pregnancy rate was reduced in TG ON females when compared with all other groups, and infertility was associated with elevated leptin levels. In addition, high leptin levels were associated with increased NPY expression, suggesting reduced leptin-signaling capacity, which may contribute to suppression of the reproductive axis in oGH animals.

Dissociation of body growth and adipose deposition effects of growth hormone in oMt1a-oGH transgenic mice

Chronic highly elevated expression of a growth hormone (GH) transgene enhances overall body growth with minimal adipose accretion, while moderate levels of circulating GH fail to enhance body growth yet promote adipose deposition. These findings suggest that the growth response to GH can be dissociated from adipose effects. This hypothesis was tested in the oMtla-oGH transgenic mouse model by titrating circulating GH levels through variable induction of transgene expression. Circulating GH levels in female transgenics were approximately 49, 132, and 750 ng/ml in response to the transgene stimulus at 0, 15, and 25 mM zinc sulfate, respectively. The highest level of circulating GH generated the largest body weight with the smallest fat accrual while the intermediate GH level generated a body weight equivalent to that for the highest GH but the heaviest gonadal fat pads. The lowest GH levels did not increase body size but did enlarge fat depots. Animals exposed to the highest level of GH had an extended growth phase relative to lower GH levels and the nontransgenic controls. In contrast, the duration of the growth phase for the 0 and 15 mM zinc stimulated transgenics was abbreviated relative to the growth phase of the control animals. The two highest levels of circulating GH increased all forms of the GH receptor, IGF-I, and hepatic lipoprotein lipase mRNA. The growth differential observed for the 0 vs. the 15 mM zinc stimulated transgenics may reflect the preferential increase in the full length GH receptor mRNA and the induction of the smaller IGF-I transcripts with the higher circulating GH while the lipid accrual paralleled the disproportionate induction of the truncated GH receptor mRNA form. Liver and bone content of zinc, manganese, copper, and iron primarily reflected dietary zinc supplementation and did not appear to play a role in the differential growth response. The dissociation of GH effects on growth and adipogenesis as a function of circulating GH levels suggests that the level of GHR and IGF-I expression acts through a threshold mechanism and low expression results in adipogenesis while high expression generates body growth.

Alendronate affects long bone length and growth plate morphology in the oim mouse model for Osteogenesis Imperfecta

Alendronate, a bisphosphonate drug, has shown promise in reducing remodeling and bone loss in postmenopausal osteoporosis. Alendronate acts directly on the osteoclast, inhibiting its resorption capability. This inhibition of osteoclast activity has led to the use of bisphosphonates in the treatment of the osteogenesis imperfecta condition. Treatment of osteogenesis imperfecta with bisphosphonates enhances bone strength, but the consequences on linear bone growth are not well defined. Using the oim mouse model for type III osteogenesis imperfecta, two doses of alendronate, low (0.125 mg/kg/wk) and high (2.5 mg/kg/wk) were administered weekly via intraperitoneal injection starting at 4 weeks of age and ending at 12 weeks of age to assess the effects of alendronate on humerus and ulna length. The higher dose of alendronate reduced humerus and ulna length in the oim/wt and wt/wt genotypes for both sexes (P < 0.05). The oim/oim humerus and ulna were not significantly affected by the higher dose of alendronate in females, but reduced bone length in males (P < 0.0085). Proximal humerus growth plate area was affected by both genotype and alendronate dose and growth plate diameter was increased at the chondro-osseous junction by both alendronate doses (P < 0.011). Genotype and alendronate dose affected growth plate height. The oim/oim genotype displayed taller growth plates. The high dosage of alendronate increased overall growth plate height, particularly within the hypertrophic zone, which suggests a failure of vascular invasion-induced apoptosis in the hypertrophic cells. In conclusion, these results indicate that high doses of alendronate (>2.5 mg/kg/wk) inhibit long bone length in mice through alteration of the growth plate and possibly reduced resorption at the chondro-osseous junction.

The genetics of epilepsy in the Belgian tervuren and sheepdog

Idiopathic epilepsy is characterized by recurrent seizure activity without an identifiable underlying anatomic defect. Dogs experiencing repeated bouts of severe seizures are given therapeutic medication to control their frequency and severity. Idiopathic epilepsy has been reported in many dog breeds and was identified as the predominant health issue facing dog breeds in a recent survey by the American Kennel Club. A growing body of evidence supports a hereditary basis for idiopathic epilepsy, with a variety of genetic inheritance models proposed. In the Belgian tervuren and sheepdog, epilepsy is highly heritable with a polygenic mode of inheritance, though apparently influenced by a single autosomal recessive locus of large effect. In an effort to establish molecular linkage between the epileptic phenotype and the locus of large effect, we have screened genomic DNA from families of affected tervuren and sheepdogs with 100 widely dispersed, polymorphic canine microsatellite markers (0.595 average PIC value). Although not significant (LOD scores <3.0), three genomic regions have shown nominal linkage between markers and the epileptic phenotype. Additional related dogs are being screened with these and additional markers to increase the power to detect the presence of a linked locus.

Heritability and complex segregation analysis of hypoadrenocorticism in the standard poodle

The heritability of hypoadrenocorticism (Addison's disease) was evaluated in 778 standard poodles with known Addisonian phenotypes. Addisonian status was confirmed clinically by adrenocorticotropic hormone (ACTH) challenge and 8.6 per cent of the poodles enrolled in the study were classified as being Addisonian. Hypoadrenocorticism affected both sexes with equal probability (P > 0.1). The most common coat colours had a negligible effect on the incidence of hypoadrenocorticism (P > 0.09), although red coat colour had a significant impact on the disease, probably due to the relatively small numbers of dogs with that coat colour. The heritability of hypoadrenocorticism in the standard poodle was estimated to be 0.75. Complex segregation analyses suggested that hypoadrenocorticism in the breed is influenced by an autosomal recessive locus. Clarification of both the heritability and mode of inheritance of hypoadrenocorticism in the standard poodle allows for better-informed breeding decisions.

Alternatives to blood as a source of DNA for large-scale scanning studies of canine genome linkages

Participation and compliance are critical to the success of any large-scale study of canine disease using DNA markers. Most canine genetic studies rely upon DNA extracted from peripheral blood samples. We assessed the utility of buccal swab epithelial cells and toe nails as a source of DNA for use in genomic screening studies. Using eight multiplexed canine microsatellite markers, amplified DNA obtained from peripheral blood, and from freshly extracted buccal epithelial cells, and buccal swab DNA extracted and stored at 20 degrees C for 27 months or extracted from toe nails were compared for three dogs. The accuracy of the genotyping at each locus was identical for each preparation. Buccal swab DNA samples were readily and uniformly amplified and could be stored for years without loss of integrity. Each buccal swab provided sufficient DNA for more than 200 individual PCR reactions. Toe nails provided ample DNA for thousands of PCR reactions and had the added advantage of ease of storage of the original tissues. These studies demonstrate the potential utility of DNA derived from buccal swabs or nails in large-scale genomic scanning and marker linkage studies.

Growth of Holstein calves from birth to 90 days: the influence of dietary zinc and BLAD status

The main objective of this study was to describe Holstein neonatal growth and development as influenced by dietary zinc supplementation and the CD18 genotype, both of which may affect immune competence. Holstein calves (n = 421), after being fed colostrum, were brought to a calf facility, randomly assigned to one of four zinc supplementation groups (control at 40 mg Zn/kg DM or the control diet supplemented with an additional 60 mg Zn/kg DM provided as either zinc sulfate, zinc lysine, or zinc methionine), weighed, and measured for morphometric growth parameters. Measurements were repeated at 30, 60, and 90 d. Calves were also genotyped for the presence of the mutant D128G CD18 allele, which, if present in two copies, causes bovine leukocyte adhesion deficiency. Zinc supplementation above 40 mg Zn/kg DM, regardless of the chemical form, did not accelerate growth (P > 0.25). Further, overall calf growth performance was not suppressed or improved (P > 0.4) in calves heterozygous at the CD18 locus relative to calves homozygous for the normal CD18 allele, although genotype negatively affected some morphometric measurements (P < 0.05). Using these data, quadratic models of early growth were generated as a preliminary step to develop growth criteria that will allow producers, veterinarians, and animal scientists to identify poor growth performance early in neonatal life. Such criteria provide the basis for tools to improve economic performance.

Effects of pre and antenatal elevated and chronic oMt1a-oGH transgene expression on adipose deposition and linear bone growth in mice

Exposing growing oMtla-oGH transgenic mice with the regulatable metallothionein promotor to elevated growth hormone (GH) for three weeks after weaning enhances bone length and adipocyte differentiation. The objective of the present study was to investigate the consequences of highly elevated GH exposure during fetal and early postnatal growth periods on the mature phenotype. Transgene expression, hence elevated GH, was achieved in fetuses and neonates by providing 25 mM ZnSO4 to the drinking water of the dams. Wildtype and oMtla-oGH male and female mice were a) never exposed to the transgene stimulus, b) exposed from birth to 21 d of age, c) exposed through gestation until 21 d of age, d) exposed only through gestation, or e) exposed only during the first 7 d postpartum. At 84 d of age when mature body size was reached, ulna and humerus lengths, and body, liver gonadal fat pad, mesenteric fat pad, and cleaned gastrointestinal (GI) tract weights were recorded. Bone lengths were also determined in a subset of mice at 22 d of age. While early exposure to the elevated GH increased ulna and humerus length at 22 d of age, the early GH levels failed to produce significant changes in adipose content or bone lengths at maturity. However, chronic exposure to slightly elevated GH, as seen in the transgenics never induced to express the transgenic GH, depressed liver and GI weights and increased adipose depot weights and humerus lengths across both sexes. These results suggest that certain tissues in the body, while capable of responding to GH during early developmental periods, are not fully entrained to sustain that growth response once the GH stimulus is withdrawn. Further, the preadipocyte pool appears unable to respond to GH early in development. Finally, the tissues examined exhibited a differential response to the GH suggesting that different tissues possess distinct response thresholds.

Growth hormone and fertility in oMt1a-oGH transgenic mice

Female mice carrying a regulatable growth hormone transgene (oMt1a-oGH) are subfertile when the transgene is actively expressed. This study was designed to characterize subfertility caused by increased concentrations of growth hormone. In particular, this study aimed to: (i) determine the effects of transgene activation and inactivation on mating, conception, maintenance of pregnancy, ovulation rate, litter characteristics and embryonic survival at day 17 of pregnancy, (ii) characterize oestrous cyclicity in transgenic versus wild-type female mice, and (iii) correlate corticosterone concentrations with transgene expression and reproductive performance. Transgenic and wild-type female mice were allocated randomly to one of four treatment groups at weaning: (i) transgenic female mice that always express the transgene, (ii) transgenic female mice that never express the transgene, (iii) transgenic female mice that express the transgene for up to 8 weeks of age and (iv) non-transgenic wild-type female mice receiving the transgene stimulus until 8 weeks of age. Activation followed by inactivation of the transgene resulted in an increased incidence of remating, resulting in an extended interval to establish pregnancy in comparison with all other treatment groups. Transgenic mice that always expressed the transgene and those that expressed the transgene for up to 8 weeks of age had lower pregnancy rates and higher ovulation rates compared with mice from other treatment groups. Both embryonic survival and the duration of the oestrous cycle did not differ among treatment groups. Active expression of the transgene resulted in an increase in the plasma concentration of corticosterone, which was associated with reduced fertility. These data indicate that the presence of a high growth hormone concentration impedes the establishment and maintenance of pregnancy. Increased plasma corticosterone concentrations may interfere with implantation as well as potentiate leptin resistance, which has been reported previously in studies with these mice.

Stability of alternatively spliced IGF-I mRNA in growth plate chondrocytes

Insulin-like growth factor-I (IGF-I) enhances the proliferation and hypertrophy of growth plate chondrocytes leading to increased growth plate width thus promoting bone elongation. Differing quantities of the multiple IGF-I transcripts within the growth plate suggest differential regulation of IGF-I. To assess this, the relative stabilities of the 1Ea, 1Eb, and 2Ea IGF-I mRNA classes in 2-6 week old rat growth plates were evaluated. The mean estimated half-life of class 1Ea was 3.7+/-0.05 h, while classes 1Eb and 2Ea decayed gradually over the course of the experiment. Estimated half-lives for each IGF-I mRNA species were unchanged at all ages examined. Incubation with Act D enhanced the transcription of class 1Ea, 1Eb, and 2Ea mRNAs to varying degrees. This implies that the differential stability of alternative IGF-I mRNA classes may be an inherent regulatory component that is not influenced by an animal's developmental state, and the differential abundance of alternative IGF-I mRNA species in the growth plate throughout development is due to transcriptional differences.

Gender effects in hearing loss in Dalmatians

Brainstem auditory-evoked-response data were collected from 3101 Dalmatian dogs from 1984 to 1998 at the Veterinary Medicine Teaching Hospital at the University of California, Davis. Also collected were data on eye color and the presence or absence of a color-patch at birth. Our objective was to evaluate the role of gender in hearing loss, including the possibility that the probability of suffering unilateral or bilateral deafness was greater if the dam was hearing impaired than if the sire was hearing impaired. Results of a multiple-trait threshold-model analysis support the commonly held observation that females were more likely to be deaf than males. In addition, females were also more likely to have two blue eyes (a condition associated with an increased prevalence of deafness). However, gender differences in hearing loss were limited to these direct observations. There was no detectable difference in the prevalence of hearing loss between offspring of deaf mothers and the offspring of deaf fathers. Finally, there was no detectable decrease in the prevalence of hearing loss over the years covered in the data set - suggesting that Dalmatian breeders are not yet selecting against hearing problems.

Obesity and elevated plasma leptin concentration in oMT1A-o growth hormone transgenic mice

OBJECTIVE

This study was undertaken to evaluate plasma leptin concentration in the regulatable ovine metallothionein-ovine growth hormone (oMT1a-oGH) transgenic (TG) mouse model of obesity.

RESEARCH METHODS AND PROCEDURES

Transgene stimulus (zinc) was provided at 21 days of age to male and female wild-type (WT) and TG mice. Plasma leptin concentrations were measured by radioimmunoassay at 42, 63, 84, and 105 days of age and from inactivated TG mice at 84 and 105 days.

RESULTS

WT and TG mice did not differ significantly in plasma leptin concentration at any of the ages examined (42, 63, 84, and 105 days), although females showed consistently higher plasma leptin concentrations than males regardless of genotype throughout the duration of the study. Male and female TG mice in which the transgene was inactivated at 63 days had a 1.5-fold to 3.5-fold increase in plasma leptin concentration over WT mice and continuously activated TG mice at 84 and 105 days of age. The elevated plasma leptin concentration seen in the inactivated TG mice at 84 and 105 days of age reflects the >300% increase in white adipose tissue seen in this model and correlated with all adipose depot weights and overall body lipid at these later ages. When plasma leptin was expressed per gram of total body fat, the leptin adjusted for body lipid was significantly higher in WT mice than either continuously activated TG or activated and then inactivated TG groups.

DISCUSSION

The inactivated TG mice in this study had higher plasma leptin levels with increasing total body adiposity, but the relative proportion of circulating leptin, on a total body lipid basis, was reduced when compared with the WT mice. This reduction was also observed in activated TG mice at the older ages. Although the absolute levels of circulating leptin were elevated in the inactivated TG animals, the amount of leptin produced per gram of fat was lowered. With the inactivation of the transgene, the leptin remained depressed after the removal of the elevated growth hormone. This represents a potential explanation for the ensuing hypertrophy of the fat depots and the abnormal phenotypic response of inactivated TG mice to elevated plasma leptin concentrations resulting in the development of obesity.

Segregation analysis of epilepsy in the Belgian tervueren dog

In 1986, a survey of the incidence of epileptic seizures among dogs in the American Belgian Tervuren Club was undertaken. By 1989, 557 of the 607 members had returned completed surveys, providing seizure information about 938 dogs. The survey classified the dogs into one of four categories: 1) no seizures observed (738 dogs); 2) one seizure observed (26 dogs); 3) two to five seizures observed (82 dogs); and 4) more than five seizures observed (92 dogs). To evaluate the plausibility of a major gene model, a regressive logistic model was applied to these data. The results suggest that a single locus with a large effect on the incidence of seizures may be segregating in this population.

Complex segregation analysis of deafness in Dalmatians

OBJECTIVE

To use pedigree analysis to evaluate the feasibility of a major locus model for deafness in Dalmatians.

ANIMALS

605 purebred Dalmatians from 42 families.

PROCEDURE

Hearing loss was evaluated through the brainstem auditory-evoked response. Dogs were classified into mutually exclusive categories: normal hearing, unilaterally deaf, or bilaterally deaf. Information was collected on sex, coat color, presence or absence of a color patch at birth, and eye color. Statistical analyses were performed by use of regressive logistic models designed for complex segregation analysis. Genetic correlations among eye color, deafness, and color patch were estimated.

RESULTS

Prevalence of hearing loss was 11% for dogs classified as unilaterally deaf and 5% for dogs that were bilaterally deaf. Complex segregation analysis detected statistical evidence of a single allele with an expected frequency of 0.21 that had an effect on the prevalence of deafness. Results of analyses suggested that this locus cannot completely explain the inheritance and incidence of deafness in Dalmatians. Genetic correlation estimates among deafness, eye color, and color patch revealed strong interrelationships among these characteristics.

CONCLUSIONS AND CLINICAL RELEVANCE

To reduce the incidence of hearing loss in Dalmatians, unilaterally deaf, blue-eyed dogs should not be considered as potential parents.

Spatiotemporal expression of alternatively spliced IGF-I mRNA in the rat costochondral growth plate

IGF-I acts as a local proliferation and maturation factor for chondrocytes in the growth plate. However, the expression of different alternative IGF-I mRNA classes in the growth plate has not been characterized. Using quantitative reverse transcription PCR, the abundance of each alternative IGF-I mRNA class in resting, proliferative and hypertrophic chondrocytes was measured in rat costochondral growth plates. Class 1Ea mRNA was the most abundant IGF-I transcript overall and was highly expressed in proliferative chondrocytes at 2 and 4 weeks of age; by 6 weeks, the majority of 1Ea mRNA expression had shifted to hypertrophic chondrocytes. Class 1Eb mRNA was the second most abundant transcript and its distribution was uniform across all the cell types at 2 weeks of age. The expression pattern changed with increasing age such that at 6 weeks a gradient existed with hypertrophic chondrocytes expressing higher levels of 1Eb than resting chondrocytes. Class 2Ea mRNA was constitutively expressed at low levels across the growth plate at all ages, while class 2Eb mRNA expression was negligible. The distribution of total IGF-I mRNA also shifted across growth plate cell types as the animals aged from 2 to 6 weeks. These findings suggest that IGF-I class 1 mRNA plays the predominant role in the maturation of the growth plate.

Consequences of limited exposure to elevated growth hormone in the mature oMt1a-oGH transgenic mouse

Male and female transgenic mice carrying the regulatable ovine metallothionein-ovine growth hormone (oMt1a-oGH) transgene were exogenously induced to express elevated GH at maturity. Male transgenics responded to continuously elevated GH with smaller white adipose tissue depots (WAT); cessation of transgene stimulation with restoration of basal circulating GH ablated the improvement in WAT. Transgenic males in which the transgene was never exogenously activated expressed low levels of oGH (60.2 ng/ml) and this low, chronic level resulted in 30-50% larger (p < 0.05) gonadal, inguinal, and mesenteric WAT relative to all wildtype controls, transgenics actively expressing the transgene, or transgenics exposed to elevated GH for a limited time. Mature females continued to accrue body mass proportional to circulating GH. Similar to that observed in the males, transgenic females in which the transgene was never exogenously activated exhibited enlarged WAT that were 20-40% larger than the same depots in wildtype control females. However, in contrast to the data for the males, transgenic females that had experienced a four week exposure to elevated GH followed by a return to basal conditions tended to have the greatest WAT depots (p < 0.10). This would indicate that female adipocytes are still capable of responding to elevated GH with proliferation/differentiation at maturity. These data support the hypothesis that the generalized sexual dimorphic pattern of lipid deposition may be attributed to the sexually dimorphic pattern of GH experienced by the two sexes.

Overexpression of growth hormone affects alternatively spliced IGF-I mRNA expression in oMt1a-oGH transgenic mice

Restorative growth hormone (GH) treatment of hypophysectomized rats differentially enhances the transcription of alternative IGF-I mRNA classes in liver. The goal of the present study was to determine the effects of GH overexpression on various classes of hepatic IGF-I mRNA in GH transgenic mice. Unstimulated oMt1a-oGH transgenic mice had low levels of transgene expression, and therefore were used to determine the effects of long-term, slightly elevated GH levels on the abundance on each alternative IGF-I mRNA class. The acute effects of high GH levels on the expression of alternative IGF-I mRNA were studied by gavaging transgenic mice with 25 mM zinc sulfate to activate oMt1a-oGH transgene expression. Long-term, low levels of oGH transgene expression in unstimulated transgenic mice resulted in a 73% down regulation of IGF-I 2Ea mRNA but not 1Ea and 2Eb mRNA. Acute stimulation of transgene expression triggered a rapid, 240% increase in 1Ea mRNA levels within 4 hours of transgene expression while 2Ea mRNA was down regulated to nearly non-detectable levels by 6 hours. IGF-I 2Eb mRNA was not affected by the short-term GH elevation. Our results showed that IGF-I 1Ea and 2Ea mRNA were differentially regulated by chronic low or acute high levels of GH. These results suggest that the regulation of IGF-I 1Ea and 2Ea mRNA transcription involve different postreceptor molecules and/or feedback mechanisms.

Alternative splicing of insulin-like growth factor I mRNA is developmentally regulated in the rat and mouse with preferential exon 2 usage in the mouse

The synthesis of an IGF-I complementary RNA (cRNA) standard containing the primer sequences for each of the four IGF-I mRNA alternative transcript forms (class 1Ea, 1Eb, 2Ea and 2Eb) and a polyA+ tail allowed the determination of the absolute abundance of each form in growing rats and mice by quantitative RT-PCR. In rat liver, class 1Ea mRNA was the most abundant form representing 90% of the total IGF-I mRNA. Though the relative proportion was maintained, the absolute abundance was maximal at 4 weeks of age and had declined by 6 weeks. In contrast, class 2Ea mRNA was the predominant transcript in mouse liver (70% of total IGF-I mRNA) and the 2Eb mRNA form was also 10-fold higher than that detected in rat liver. These results suggest that rats and mice differ both in their transcription initiation at two leader exons and in their alternative splicing activities for exon 5.

Reducing the incidence of epileptic seizures in the Belgian Tervuren through selection

There is growing evidence that idiopathic epilepsy in the Belgium Tervuren has a genetic foundation. Reducing the incidence of this disorder, which may afflict as much as 17% of the breed, will rely upon the wise selection of parents. Seizure data on 997 dogs from the American Belgian Tervuren Club were collected through questionnaires in which animals were classified into one of four mutually exclusive categories: 1) no seizures observed, 2) one seizure observed, 3) two to five seizures, and 4) more than five seizures. The analysis of this ordered data made use of a threshold model of Bayesian inference. Integration of posterior densities was accomplished through Gibbs sampling. Through this analysis we are able to predict that the offspring of the mating of two non-epileptic dogs has a probability of 0.99 of never suffering from a seizure. The offspring of the mating of two dogs who have each had 1 seizure has a predicted probability 0.58 of never suffering from a seizure. Prevention of this disease is best prescribed through the selection of non-epileptic dogs as parents of future generations.

Heritability of epileptic seizures in the Belgian tervueren

Survey data were collected on the incidence of epileptic seizures in 997 Belgian tervuerens. The heritability of this disorder was estimated as 0.77 (with a 95 per cent confidence interval spanning from 0.65 to 0.88) using a Bayesian analysis in an ordered categorical threshold model. Single locus models do not appear adequate as an explanation for this inherited seizure disorder. The high heritability estimate suggests that breeders can wage a successful battle against this disorder by breeding unaffected individuals, particularly those from families with no history of seizures.

Body composition of inactivated growth hormone (oMt1a-oGH) transgenic mice: generation of an obese phenotype

The consequences of a 42 d exposure to elevated growth hormone (GH) on adipose tissue were assessed using the regulatable ovine metallothionein- ovine GH (oMt1a-oGH) transgene in male and female GH transgenic (TG) mice. Activation of transgene expression at 21 d of age followed by inactivation of transgene expression at 63 d of age (TG-on/off) increased individual white adipose tissue (WAT) depots and total body lipid stores in both males and females. WAT, expressed as a percentage of fasted body weight, did not differ in wildtype (WT) and continuously activated TG males and females up to 105 d of age, but was increased approximately 270% following inactivation of the transgene. Inguinal depot adipocytes were more numerous in both male and female TG +/- relative to WT or TG animals. The ensuring obesity was not accompanied by a decrease in thermogenic capacity of brown adipose tissue, as indexed by uncoupling protein quantity. GH transgene expression was accompanied by elevated insulin levels that were restored to WT levels upon cessation of transgene expression (p > 0.1). Early, transient exposure to elevated GH increased total body lipid by nearly threefold independent of gender; the increased lipid content was sustained and reflected WAT hypertrophy and hyperplasia. The oMt1a-oGH mouse provides a novel model of induced obesity in response to inactivation of a GH-transgene by the withdrawal of the transgene stimulus.

A threshold model analysis of deafness in Dalmatians

To elucidate the inheritance of deafness in Dalmatian dogs, 825 dogs in 111 litters were evaluated for abnormalities in hearing through the brainstem auditory evoked response (BAER). Recorded along with their quality of hearing (normal, unilaterally deaf, or bilaterally deaf) were the sex, coat color, eye color and the presence or absence of a color patch. The analysis considered deafness an ordered categorical trait in a threshold model. The underlying, unobservable continuous variate of the threshold model was assumed to be a linear function of sex of dog, coat color (black or liver and white), color patch (presence or absence), eye color, the deafness phenotype of the parents and a random family effect. Twenty-six percent of dogs were deaf in at least one ear. Eye color, color patch, sex and the hearing status of the parents were all significant contributions to deafness. The heritability of deafness, on the continuous unobservable scale, was 0.21. This value was computed after correction for eye color, color patch, parental hearing status and sex, implying that significant genetic variation exists beyond the contribution of several single loci.

Increased hepatic delta 6-desaturase activity with growth hormone expression in the MG101 transgenic mouse

Growth hormone (GH) has many metabolic effects, but its mechanism(s) of action are not fully understood. We studied the short-term effects of endogenously produced GH on liver delta 6-desaturase activity and adipose and liver lipid fraction fatty acid composition in transgenic mice. MG101 transgenic mice ages 73-114 d received zinc to activate the ovine GH transgene for 7 d. Nontransgenic littermates, used as controls, also received zinc. Liver lipids were fractionated into phospholipids (PL), cholesteryl esters, and triglycerides (TG), and retroperitoneal adipose fractionated into PL and TG for fatty acid analysis. Liver microsomes were assayed for delta 6-desaturase activity. Animals expressing the ovine growth hormone transgene had a 2.5-fold higher liver delta 6-desaturase activity than controls. Arachidonate and docosahexaenoate were significantly higher in liver PL of GH transgenic animals compared to controls, but both were decreased in adipose PL in the GH animals. We conclude that increased production of GH affects both production and organ distribution of highly unsaturated fatty acids. The changes in arachidonate in various lipid pools following transgene expression may mediate the systemic actions of GH.

Skeletal muscle growth of oMTla-oGH transgenic mice

Forty-eight transgenic mice carrying an ovine metallothionein 1a-ovine growth hormone (oMTla-oGH) transgene and 48 littermate control mice were used to investigate the effect of GH transgene on the growth and biochemical characteristics of skeletal muscle. Transgene expression was initiated in the transgenic mice by the addition of zinc sulfate to the water at 21 d of age; control mice were also supplemented with zinc sulfate. These mice were maintained on zinc sulfate until 84 d of age. Groups of mice (16 controls, 16 transgenics) were killed at 21, 42 and 84 d of age and muscles from the hind leg were dissected, weighed and analyzed. At 84 d, male transgenics were 32% heavier than controls, while female transgenics were 47% heavier. Transgenic mice of both sexes had smaller (p < 0.01) muscles than controls at weaning (21 d). In spite of significantly heavier body weights of transgenic mice at 84 d of age, there were no significant differences in muscle weights. This was due to a significantly lower (p < 0.01) proportion of muscle, expressed as percentages of body weights, in transgenic mice compared with controls. Higher DNA and RNA concentrations at 42 d of age and elevated cathepsins C and H activities at 42 and 84 d of age indicate that muscle protein metabolism is more active in transgenic mice, which are growing at a greater rate than controls from weaning to 84 d of age. The fact that oMTla-oGH transgenic mice inherently have a lower proportion of muscle, compared to controls and that this proportion does not change in spite of transgene activation and 30 fold increase in plasma GH levels, suggests the hypothesis that muscle growth may be controlled by locally produced IGFs, which are essentially independent of circulating GH concentrations.

Development of obesity following inactivation of a growth hormone transgene in mice

Mice with a temporally regulatable ovine metallothionein 1a--ovine growth hormone transgene (oMT1a-oGH) were utilized to study the effects of withdrawal of elevated circulating levels of growth hormone (GH) on growth and body composition. The transgene was activated from 21-42 days of age by provision of zinc sulfate in the drinking water. At 42 days, mice were allocated to either activated transgenic (remain on zinc sulfate) or inactivated transgenic (removal of zinc sulfate) groups, and to receive either ad libitum or restricted (80-90% of ad libitum) access to feed. Non-transgenic control mice were treated similarly. Body weights and intakes were recorded weekly. Mice were killed at 70 d and epididymal and subcutaneous fat pads, trimmed hind carcass and various organs were weighed. The main findings of this study are: (1) food-restricted mice possessing an activated oMT1a-oGH transgene fail to demonstrate increased growth, but exhibit significantly reduced levels of fat (P < 0.05) relative to all other genotype x feed level combinations; and (2) inactivation of the oMT1a-oGH transgene, following a period of elevated GH levels, leads to development of obesity as evidenced by two to three fold increases in epididymal and subcutaneous fat pad weights (P < 0.01) relative to both activated transgenic and non-transgenic control mice. These large increases in fat deposition also occurred when intake was restricted to 80-90% of ad libitum levels, indicating that metabolic changes independent of intake occur in these inactivated transgenic mice. It is possible that highly elevated production of GH in activated oMT1a-oGH transgenic mice leads to (1) enhanced promotion of preadipocyte differentiation, leading to increased numbers of adipocytes that, upon cessation of oGH production, are available for lipid deposition resulting in obesity, or (2) alterations in production of or responsiveness to insulin, leading to increased fat deposition upon removal of the chronic anti-lipogenic actions of GH. The oMT1a-oGH transgenic mouse line should provide a new genetic model with which to investigate the mechanisms by which growth hormone affects obesity.

Fractionation of growth plate chondrocytes: differential expression of IGF-I and growth hormone and IGF-I receptor mRNA in purified populations

In vitro studies of growth plate cell kinetics have been hindered by the spatial arrangement and heterogeneity of cells within the plate. In this study, we describe a fractionation method that consistently generated five relatively pure populations of growth plate chondrocytes. Each fraction exhibited morphology, proliferative rates, and marker mRNA expression consistent with in vivo positional phenotypes. In characterizing the fractional response, fibroblast growth factor was most effective in stimulating resting cells to proliferate and least effective on cells actively dividing (fraction 3). Insulin-like growth factor-I (IGF-I) was most active on fraction 3 while epidermal growth factor's mitogenic induction was equivalent across all fractions. Growth hormone receptor (GHR) mRNA was most abundant in mature hypertrophic cells and undetectable in resting cells; IGF-I receptor (IGF-IR) mRNA was detectable in resting cells but two-fold higher in the fraction adjacent to cells possessing high GHR mRNA, while proliferating and resting chondrocytes had elevated IGF-I mRNA levels when compared to that for hypertrophic chondrocytes. The growth plate distribution of IGF-IR and GHR mRNA implies distinct roles for circulating IGF-I vs. paracrine produced IGF-I.

Growth hormone and IGF-I stimulate cell function in distinct zones of the rat epiphyseal growth plate

Proliferation and maturation of growth plate chondrocytes are primarily responsible for linear bone elongation, although the exact mechanisms involved have not been fully characterized. We have used discrete chondrocyte populations to address the mode of growth hormone (GH) action on the growth plate. Low doses of GH, and insulin-like growth factor-I (IGF-I) preferentially enhanced cell proliferation in proliferative zone chondrocytes; the mitogenic response of immature proliferative and resting zone cells was minimal. Proliferation was not enhanced by combining the effects of GH and IGF-I. Exposure to IGF-I increased IGF-I mRNA in resting zone cells. Both GH and IGF-I stimulated the accumulation of IGF-I receptor mRNA in the most immature proliferative zone cells but did not alter the accumulation of IGF-binding protein 4 mRNA in any fraction. These results confirm a direct effect of GH on growth plate chondrocytes and suggest that GH preferentially acts on the actively proliferating chondrocytes.

Expression of an ovine growth hormone transgene in mice increases arachidonic acid in cellular membranes

The degree of unsaturation of membrane lipids has been implicated in a number of physiological disorders, yet its regulation remains poorly understood, especially the regulation of the synthesis and distribution of arachidonic acid levels, the most abundant long chain polyunsaturated fatty acid in membranes. Transgenic mice expressing the ovine metallothionein 1a-ovine growth hormone (oMt1a-oGH) fusion gene exhibited significantly elevated levels of a number of long chain polyunsaturated fatty acids in serum, including arachidonic acid. In oMt1a-oGH transgenic mice the products of all three desaturation pathways are affected by the expression of the ovine growth hormone transgene. The essential precursors of membrane long chain polyunsaturated fatty acids, 18:2n-6 and 18:3n-3, were reduced in transgenics relative to controls, and their desaturation and elongation products, arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3), were elevated. As rare intermediate long chain polyunsaturated fatty acids such as eicosatrienoic acid (20:3n-9) were also significantly elevated, we conclude that these observations reflect increased activity of the delta-5 and delta-6 desaturase enzymes. In contrast, the products of the stearoyl CoA or delta-9 desaturase, were significantly reduced in oMt1a-oGH expressing transgenics relative to their levels in control mice.

Regulation of insulin-like growth factor-I and binding protein-3 expression in oMtla-oGH transgenic mice

Growth hormone (GH)-transgenic mice provide a model for studying hormonal regulation of gene products responsible for efficient lean growth. Insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (BP-3) are two products involved in mediating the growth promoting actions of GH. Mice carrying the ovine metallothionein la-ovine growth hormone (oMtla-oGH) transgene were used to study GH regulation of IGF-I and BP-3 expression because these mice do not exhibit elevated basal oGH levels without transgene stimulation by exogenous zinc. C57B1/6XCBA mice with (transgenic = TG) and without control = C) the oMtla-oGH transgene were activated (+ Zn) or inactivated (-Zn) by the addition or removal of 25 mM zinc sulfate in the drinking water. Plasma IGF-I and BP-3 levels were determined by radioimmunoassay and western ligand blotting, respectively. Hepatic IGF-I and BP-3 mRNA levels were determined by slot-blot analysis. TG+Zn mice had higher plasma IGF-I (p < 0.05) and hepatic IGF-I mRNA (p < 0.05) levels as compared to TG-Zn, C+Zn and C-Zn mice. Plasma IGF-I and hepatic IGF-I mRNA levels in TG-Zn mice were not different from C+Zn and C-Zn mice. Removal of Zn decreased hepatic IGF-I mRNA levels to C levels in TG mice. Plasma BP-3 and hepatic BP-3 mRNA levels in TG+Zn mice were increased (p < 0.05) as compared to TG-Zn, C-Zn and C+Zn. Plasma BP-3 and hepatic BP-3 mRNA levels did not differ between TG-Zn, C-Zn and C+Zn mice. Expression of the transgene also increased the level of plasma BP-3 during pregnancy as compared to that observed for pregnant C mice. We conclude that oGH regulates IGF-I and BP-3 expression in the oMtla-oGH transgenic mouse model system.

Dependence of increased linear bone growth on age at oMT1a-oGH transgene expression in mice

We have previously shown that growth hormone (GH) accelerates the rate and extends the duration of linear bone growth in a GH-transgenic mouse model. To determine if this GH effect was temporally regulated, bone lengths and growth plate widths were determined in transgenic mice carrying an ovine metallothionein 1a-ovine growth hormone (oMT1a-oGH) transgene. Transgene expression was initiated in oMT1a-oGH hemizygous transgenic mice by addition of 25 mM ZnSO4 to the water at 21 d of age; littermate control mice were also ZnSO4 supplemented. These mice were maintained on ZnSO4 until 70 d of age at which time the mice were killed and the ulna, humerus, and tibia were collected. Additional transgenic and control mice were stimulated at 21 d and the ZnSO4 stimulus withdrawn after 21 d of treatment and killed at 70 d or stimulated at 28 d with the stimulus withdrawn after 28 d and killed at 70 d. Continuously stimulated transgenic mice had longer bones than those of comparable control mice. The increased bone length in the transgenics was correlated with wider growth plates. Transgene expression initiated at 21 d of age increased bone length to the same or greater extent than that observed for mice with transgene expression initiated at 28 d but maintained for a longer interval thereby indicating that the age of GH initiation is more critical in bone elongation than the duration of GH exposure. The elevated GH effects were independent of circulating thyroid hormones and attainment of puberty. Elevated GH also increased the widths of all growth plate zones to the same extent by increasing cell numbers, rather than enhancing matrix production or individual cellular area.

Gonadotrope responsiveness in orchidectomized sheep. II. Effect of gonadotropin-releasing hormone amplitude shift during continuous infusion of estradiol

Gonadotropin secretion during continuous infusion of estradiol (E2; 5 micrograms/h, i.v.) and pulsatile delivery of GnRH was assessed in orchidectomized sheep (wethers). Wethers received 200 ng GnRH per hourly pulse during the first 12 h of E2 infusion. During the final 36 h of infusion, animals (n = 6/group) received 0, 200, 400, 800, or 1600 ng GnRH/h pulse. Amplitude shift to 1600 ng GnRH/h pulse induced preovulatory surge-like secretion of LH in animals receiving concurrent E2 infusion. In the absence of E2, the same change in GnRH amplitude did not significantly affect serum concentrations of LH. Full expression of the GnRH-induced surge of LH in wethers required prior exposure to E2, but was not dependent on pretreatment with low-amplitude GnRH stimulus. In a companion experiment, anterior pituitary tissue was collected from E2-treated wethers 0, 3, 6, 12, or 24 h after initiation of episodic GnRH delivery (1600 ng/h pulse). Treatment with E2 induced a 5-fold increase in GnRH receptor concentration. The tissue concentration of GnRH receptor was depressed (p < 0.05) within 6 h of initiation of high-amplitude GnRH stimulation and remained depressed for the duration of GnRH delivery. Tissue stores of LH were increased (P < 0.05) by E2 and reduced (p < 0.05) after 3 h of high-amplitude GnRH stimulation. In contrast, tissue stores of FSH were reduced (p < 0.05) by both E2 alone and E2 with concurrent high-amplitude GnRH stimulation. The concentration of mRNA for the FSH beta subunit, but not for the alpha or LH beta subunits, was reduced (p < 0.05) by E2.(ABSTRACT TRUNCATED AT 250 WORDS)