Quantitative analysis of performance, carcass and meat quality traits in cattle from two Australian beef herds in which a null myostatin allele is segregating

Two Australian beef cattle herds, in which selection for muscularity was a primary objective, were used in this study to identify bovine myostatin (MSTN) mutations associated with increased muscling, and to assess associations between genotype and performance, carcass and meat quality traits. One was a research herd (herd A) established from Angus × Hereford cows, and comprised a high and low muscle selection line. The other (herd B) was a commercial beef enterprise with cattle of Angus and Charolais origin. Sequencing of the MSTN coding region and flanking splice junctions in an initial sample of 34 animals from both herds identified the 821 del11 mutation as well as six other polymorphic sites. The nucleotide 374–50C > T polymorphism in intron 1 was found to be in linkage disequilibrium with the 821 del11 mutation, with both variants confined to the high muscle selection line in herd A. No other variants were exclusive to either of the two herd A selection lines. The effect of the 821 del11 mutation was further investigated in a total of 803 cattle from both herds. A relatively high prevalence of 821 del11 heterozygotes (herd A 16%; herd B 23%) was found and heterozygotes had significant advantages in eye muscle area and muscle score over their wildtype counterparts, and did not differ in meat quality. Retail beef yield from steers was higher for the 821 del11 heterozygotes from herd A (67.0 v. 63.5%) and herd B (71.8 v. 68.6%), relative to homozygous wildtype contemporaries, demonstrating the benefits of incorporating single null MSTN alleles into breeding programs.

Genotyping cattle for inherited congenital myoclonus and maple syrup urine disease

OBJECTIVE

To develop a routine procedure for establishing the inherited congenital myoclonus (ICM) genotype of cattle and to obtain an estimate of the prevalence of heterozygotes for ICM and maple syrup urine disease (MSUD) in Australian Poll Herefords.

DESIGN

A mismatch amplification procedure was developed to genotype for ICM. The ICM and MSUD genotypes of subjects from a 'neuraxial oedema' experimental breeding herd were investigated. Tail hair roots were used as a source of target DNA to determine the ICM and MSUD genotypes of 455 Poll Hereford bulls.

RESULTS

An Acc I mismatch procedure was found to be suitable to genotype cattle for the ICM alleles using tail hair roots as the source of DNA. Based on the prevalence of heterozygotes among saleyard and sale bulls in the early 1990s, and contemporary slaughter bulls, the frequencies of the alleles responsible for ICM and MSUD were estimated to be between 0.01 and 0.02.

CONCLUSION

This survey demonstrates that the mutations responsible for ICM and MSUD are present in the Australian Poll Hereford population. PCR tests could be used to advantage in differential diagnosis of neurological disease in newly born calves and in selection of Poll Hereford seed stock.

Genotyping Brahman cattle for generalised glycogenosis

OBJECTIVE

To develop procedures for genotyping Brahman cattle for loss-of-function alleles within the acidic alpha-glucosidase gene and to assess the risk of generalised glycogenosis in Australian Brahman cattle.

DESIGN

PCR assays for three loss-of-function alleles were designed to exploit internal restriction sites within acidic alpha-glucosidase amplicons that are independent of allelic variants at the mutant sites.

RESULTS

Genotyping 8529 clinically normal Brahmans between August 1996 and August 2001 revealed 16.4% were heterozygous for the more common of the two mutations (1057deltaTA, often referred to as the 'E7' mutation) that cause generalised glycogenosis in this breed. The less common 1783T mutation (often referred to as the 'E13' mutation) was restricted to descendants of one imported bull, and was not detected in 600 randomly selected Brahmans. Prior to definition of these two disease-causing mutations, 640 (18%), and 14 (0.4%), of 3559 clinically normal Brahmans analysed between January 1994 and December 1996, were heterozygous, and homozygous, respectively, for a silent polymorphism (2223G-->A) that is associated with generalised glycogenosis. In addition to the 1057deltaTA and 1783T mutations, approximately 15% of Brahmans were found to be heterozygous for a single base substitution in exon 9 (1351T, commonly referred to as the 'E9' mutation) that significantly reduces acidic alpha-glucosidase activity, but has not been associated with clinical disease. These three loss-of-function alleles were found in Brahmans imported, or selected for import, from the USA.

CONCLUSION

The PCR procedures reported here represent a significant improvement in reliability and accuracy over previous published methods. Utilisation of these PCR/restriction enzyme based assays will facilitate precise selection against the 1057deltaTA and 1783T alleles, and consequently reduce the incidence of generalised glycogenosis in registered and commercial Brahman herds.

Genotyping shorthorn cattle for generalised glycogenosis

OBJECTIVE

To develop a procedure for routine genotyping of Shorthorn cattle for the generalised glycogenosis allele in exon 18 of the acidic alpha-glucosidase gene.

PROCEDURE

Allele-specific amplification and double mismatch amplification procedures for the discrimination of the exon 18 alleles were evaluated using leucocytes and hair roots as sources of target DNA.

RESULTS

Allele-specific amplification was effective for genotyping Shorthorn cattle at the 2454 site when purified DNA was used as target for the polymerase chain reaction. However, when the target DNA was derived from hair roots, differences in the relative yield of wild-type and mutant amplicons were observed. The double mismatch amplification procedure was effective in genotyping all subjects, independent of the source of DNA. The unique cleavage sites for Drd I and PshA I within exon 18 are present and absent respectively in the wildtype amplicon, and are lost and acquired, respectively, in the mutant amplicon. In addition, the Drd I and PshA I mismatching cleavage sites incorporated into the primers serve as internal controls for Drd I and PshA I cleavage.

CONCLUSION

The double Drd I/PshA I mismatch amplification procedure using hair root samples as the source of DNA is a robust method for genotyping Shorthorns for generalised glycogenosis.

A nonsense mutation in the alpha1 subunit of the inhibitory glycine receptor associated with bovine myoclonus

Inherited congenital myoclonus of Poll Hereford calves is an autosomal recessive disease characterized by hyperesthesia and myoclonic jerks of the skeletal musculature that occur both spontaneously and in response to sensory stimuli. Binding studies have previously shown that myoclonus is associated with specific loss of [(3)H]strychnine-binding sites from spinal cord and brain stem in affected calves. In order to identify the mutation responsible for myoclonus, we examined the candidate genes, glycine receptor alpha1 (Glra1) and beta (Glrb) subunits, in affected and normal cattle. A nonsense mutation was found at amino acid 24, located in exon 2 of the Glra1 gene in both cDNA and genomic sequences from affected but not control animals. Immunohistochemistry, with a monoclonal antibody to alpha and beta subunits of the glycine receptor, revealed a loss of cell surface immunoreactivity in myoclonic animals, suggesting a failure in the assembly of the receptor that could explain the characteristic phenotype of the disease.

The bovine alpha-glucosidase gene: coding region, genomic structure, and mutations that cause bovine generalized glycogenosis

We report here cDNA and genomic sequence of the bovine acidic alpha-glucosidase gene, from the initiation codon to the most 3' polyadenylation signal. The 2814-bp coding sequence predicts a 937-amino acid protein, which is highly conserved compared with the human alpha-glucosidase gene (86% and 83% identity respectively). The intron/exon boundaries are also conserved between the two species. Two mutations have been identified in Brahmans, and one in Shorthorns, that lead to generalized glycogenosis. All three mutations result in premature termination of translation. Evidence is also presented for a missense mutation segregating with the Brahman population, which is responsible for a 70-80% reduction in alpha-glucosidase activity.

Definition of the mutation responsible for maple syrup urine disease in Poll Shorthorns and genotyping Poll Shorthorns and Poll Herefords for maple syrup urine disease alleles

The organisation of the E1alpha subunit of bovine branched-chain alpha-keto acid dehydrogenase gene was established. c DNA was cloned from Poll Shorthorn x Poll Hereford calves affected with Maple Syrup Urine Disease to identify the mutation responsible for the disease in Poll Shorthorns. Clones containing the c DNA sequences inherited from the Poll Shorthorn sire of the affected calves were identified. Paternal clones were sequenced and a cytidine to thymidine transition was found at nucleotide 1380. The mutation is predicted to substitute leucine in place of a highly conserved proline at codon 372. A polymerase chain reaction procedure was developed for detection of the 1380C-->T mutation in genomic DNA. Three Poll Shorthorn parents of affected calves and three affected Poll Shorthorn x Poll Hereford calves were heterozygous and an affected Poll Shorthorn calf was homozygous for this mutation. An improved polymerase chain reaction procedure was also devised to genotype Poll Herefords for the 248C-->T mutation. The procedures will facilitate disease prevention programs and assist in differential diagnosis of conditions in new-born calves that present with a rapid onset of progressive neurological disease and are characterised histologically by 'status spongiosus'. Maple Syrup Urine Disease (MSUD) is an autosomal recessive defect reported in humans (Danner and Elsas 1989), and in Poll Hereford (PH) and Poll Shorthorn (PS) calves (Harper et al 1986, Healy et al 1992). The clinical, biochemical and pathological manifestations of the disease are identical in the two breeds of cattle, and are characterised by the rapid onset of progressive neurological disease, leading to death within a few days of birth. The disease is caused by a deficiency of activity of the mitochondrial enzyme branched-chain alpha-keto acid dehydrogenase (BCKADH). This deficiency leads to elevated concentrations, in blood and tissues, of branched chain alpha-keto acids and their precursors, the branched chain amino acids, valine, leucine and isoleucine. BCKADH consists of four subunits E1alpha, E1beta, E2 and E3 that are encoded by separate genes, and MSUD may result from deficiency of any of the subunits. In PH s, the disease in caused by premature termination of translation, of the E1alpha subunit, that is induced by a cytidine to thymidine transition exon 2 (248C-->T), that converts the glutamine codon -6 to a stop codon (Q-6ST; Zhang et al 1990). We have shown that MSUD -affected PSxPH calves are heterozygous at the PH locus, illustrating molecular heterogeneity exists for bovine MSUD (Healy and Dennis 1994a). The fact that these crossbred calves are affected, indicates the PS, like the PH mutation, resides in the E1alpha subunit.

Hepatocyte gene therapy in a large animal: a neonatal bovine model of citrullinemia

The development of gene-replacement therapy for inborn errors of metabolism has been hindered by the limited number of suitable large-animal models of these diseases and by inadequate methods of assessing the efficacy of treatment. Such methods should provide sensitive detection of expression in vivo and should be unaffected by concurrent pharmacologic and dietary regimens. We present the results of studies in a neonatal bovine model of citrullinemia, an inborn error of urea-cycle metabolism characterized by deficiency of argininosuccinate synthetase and consequent life-threatening hyperammonemia. Measurements of the flux of nitrogen from orally administered 15NH4 to [15N]urea were used to determine urea-cycle activity in vivo. In control animals, these isotopic measurements proved to be unaffected by pharmacologic treatments. Systemic administration of a first-generation E1-deleted adenoviral vector expressing human argininosuccinate synthetase resulted in transduction of hepatocytes and partial correction of the enzyme defect. The isotopic method showed significant restoration of urea synthesis. Moreover, the calves showed clinical improvement and normalization of plasma glutamine levels after treatment. The results show the clinical efficacy of treating a large-animal model of an inborn error of hepatocyte metabolism in conjunction with a method for sensitively measuring correction in vivo. These studies will be applicable to human trials of the treatment of this disorder and other related urea-cycle disorders.

Evaluation of gene therapy for citrullinaemia using murine and bovine models

Citrullinaemia is an autosomal recessive disorder caused by the deficiency of argininosuccinate synthase. The deficiency of this enzyme results in an interruption in the urea cycle and the inability to dispose of excess ammonia derived from the metabolism of protein. The only treatment for this disorder has been dietary restriction of protein and supplementation with medications allowing for alternative excretion of excess nitrogen. Gene therapy offers the possibility of a long-term cure for disorders like citrullinaemia by expressing the deficient gene in the target organ. We have explored the use of adenoviral vectors as a treatment modality for citrullinaemia in two animal models, a naturally occurring bovine model and a murine model created by molecular mutagenesis. Mice treated with adenoviral vectors expressing argininosuccinate synthase lived significantly longer than untreated animals (11 days vs 1 day; however, the animals did not exhibit normal weight gain during the experiment, indicating that the therapeutic effectiveness of the transducing virus was suboptimal. It is speculated that part of the failure to observe better clinical outcome might be due to the deficiency of arginine. In the bovine model, the use of adenoviral vectors did not result in any change in the clinical condition of the animals or in the level of plasma ammonia. However, the use of 15N isotopic ammonia allowed us to assess the flux of nitrogen through the urea cycle during the experiment. These studies revealed a significant increase in the flux through the urea cycle following administration of adenoviral vectors expressing argininosuccinate synthase. We conclude that the use of adenoviral vectors in the treatment of citrullinaemia is a viable approach to therapy but that it will be necessary to increase the level of transduction and to increase the level of enzyme produced from the recombinant viral vector. Future experiments will be designed to address these issues.

Molecular heterogeneity for bovine alpha-mannosidosis: PCR based assays for detection of breed-specific mutations

DNA tests, based on the polymerase chain reaction (PCR), were developed for the detection of two breed-specific mutations responsible for the autosomal recessive disorder bovine alpha-mannosidosis. The tests involve separate amplification of two exons of the lysosomal alpha-mannosidase gene followed by restriction enzyme digestion of the amplicons. We demonstrate that one of the mutations, the 662G-->A transition, is responsible for alpha-mannosidosis in Galloway cattle. The other mutation, the 961T-->C transition, is uniquely associated with alpha-mannosidosis in Angus, Murray Grey and Brangus cattle from Australia. The 961T-->C mutation was also detected in Red Angus cattle exported from Canada to Australia as embryos. All 39 animals classified as heterozygotes on the basis of biochemical assays were heterozygous for one of the two mutations. None of 102 animals classified as homozygous-normal on the basis of biochemical assays possessed the mutations. Our results indicate that the two breed-specific mutations may have arisen in Scotland and by the export of animals and germplasm disseminated to America, New Zealand and Australia.

Testing for undesirable traits in cattle: an Australian perspective

A variety of autosomal recessive defects, many lethal to the newborn calf, have been recognized in Australia. Definition of a defect at the biochemical or molecular level facilitates development of heterozygote detection tests essential for efficient disease control programs. The prevalence of alpha-mannosidosis in Angus and Murray Greys, generalized glycogenosis in Brahmans and Shorthorns, and citrullinemia in Holstein/Friesians has been reduced as a result of industry-sponsored disease-control programs. These defects were disseminated as a consequence of selection focused on desirable traits carried by individuals. In the long term, an increase in crossbreeding in commercial beef production will reduce the significance of recessive defects. Caution will be required to reduce the risk of dissemination of recessive defects resulting from increased selection pressure within the dairy industry presently dominated by Holstein/Friesians.

Heterozygote detection for maple syrup urine disease in cattle

The clinical, pathological and biochemical manifestations of maple syrup urine disease (MSUD) are similar in Poll Hereford and Poll Shorthorn x Poll Hereford calves. No significant differences were observed in branched-chain amino acid concentrations in plasma, or of branched-chain keto acid dehydrogenase activity in fibroblasts, between Poll Herefords homozygous normal and heterozygous for the mutation responsible for MSUD. Haemopoietic chimerism resulted in incorrect diagnosis of the MSUD genotype in 30% of non-identical twins when blood DNA was analysed using allele-specific amplification. Hair roots are shown to be a suitable source of target DNA for genotyping Poll Hereford cattle for the MSUD mutation. Twelve of 203 (5.8%) aged Poll Hereford bulls, sampled at saleyards during the last 4 months of 1993, were found to be heterozygous for the mutation. In contrast, the mutant sequence was detected in only 1 of 150 (0.7%) 2- and 3-year-old Poll Hereford bulls offered for sale at 2 stud sales held during 1993, suggesting that the prevalence of the disease may decline over the next few years.

Evidence of molecular heterogeneity for generalised glycogenosis between and within breeds of cattle

Northern analyses revealed normal levels of acidic alpha-glucosidase mRNA in cultured fibroblasts from a Shorthorn calf affected with glycogenosis but a gross deficiency in an affected Brahman calf. Analyses of acidic alpha-glucosidase activity, relative to that of other lysosomal enzymes, in blood mononuclear cells revealed greater variation within and between Brahman herds than Shorthorn herds. A Msp1 restriction fragment length polymorphism associated with glycogenosis in Brahmans was not found in Shorthorns. These results are considered in relation to molecular heterogeneity for AAG deficiency in cattle and its implications for disease control programs.

Molecular heterogeneity for bovine maple syrup urine disease

In Poll Herefords, it is known that maple syrup urine disease results from a nonsense mutation in codon -6 of the gene for the E1 alpha subunit of branched-chain alpha-keto acid dehydrogenase. The disease also occurs in Poll Shorthorns, but its molecular basis in this breed has not yet been determined. Allele-specific hybridization and allele-specific amplification, both based on the Poll Hereford mutation, failed to detect the mutant allele in Poll Shorthorn heterozygotes, and detected the normal allele in affected Poll Hereford-cross-Poll Shorthorn calves. These results demonstrate between breed molecular heterogeneity for bovine maple syrup urine disease.

Haemopoietic chimaerism: a complication in heterozygote detection tests for inherited defects in cattle

Several observations are documented which illustrate that haemopoietic chimaerism is a potential source of error when using assays of cellular components of blood to determine genotype for inherited defects in cattle. Acidic alpha-glucosidase activity in peripheral mononuclear cells of a twin Brahman bull that had sired calves affected with generalized glycogenosis was similar to that in cells from homozygous normal animals. Activity in fibroblasts from this bull was similar to that in heterozygotes. alpha-mannosidase activity in fibroblasts of a twin Murray Grey bull with low activity in peripheral granulocytes but high activity in plasma was similar to that in animals homozygous normal for alpha-mannosidosis. Normal argininosuccinate synthetase nucleotide sequence was detected in leucocytes from two calves affected with citrullinemia and mutant sequence detected in leucocytes from their homozygous normal co-twins.

Inherited enzyme deficiencies in livestock

The biochemical basis of over 300 inherited diseases has been defined in humans, and the majority involve abnormalities in enzymes. The rate of discovery of new defects is accelerating as biochemical and molecular technologies improve. The majority of inherited defects are expressed before puberty and approximately 25% are apparent at birth. Genomes of other mammals are similar and have been subjected to similar mutation pressures; therefore, it is probable that a range of inherited defects exists in livestock similar to that in humans. Because modern livestock populations have emerged from small population bases, the range of genetic aberrations, within breeds, will be less than in the general human population. Even if there is a 10-fold difference, however, there will be a bewildering array of defects possible in each breed. Because the level of inbreeding within livestock populations is greater than in the general human population, on the other hand, the prevalence of specific defects will be higher. It is probable that a high prevalence of a lethal recessive defect could occur within a particular livestock population and escape recognition. First, livestock producers accept a relatively high neonatal mortality rate without seeking a diagnosis. Second, few if any veterinary diagnostic facilities possess either the instrumentation or the analytic skills essential for investigating the vast range of potential inborn errors of metabolism. Third, national selection programs--e.g., those employed within the dairy industry--tend to use production data from adult progeny in selection. Consequently, the programs would not detect differences in fetal or neonatal mortality rates among descendants of specific sires until a deleterious defect had been widely disseminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine ceroid-lipofuscinosis: Pathology of blindness

Five Devon cattle with suspected ceroid-lipofuscinosis and aged between 19 and 39 months of age were humanely slaughtered and subjected to post-mortem examination. There was severe atrophy of the cerebrum, particularly of the occipital cortex. Microscopy also showed severe atrophy of the retina with complete loss of photoreceptor cells, even in the youngest animal examined. Histopathologically the disease was characterised by accumulation of a fluorescent lipopigment in neurones, including those of the retina and a severe astrocytosis. The disease, which is characterised by the accumulation of subunit c of mitochondrial ATP synthase, is similar to that extensively described in South Hampshire sheep except that the retinal lesions were more severe. In contrast, tremors were not noted in the cattle. The clinical history and similarity to the disease in sheep and other species indicated inheritance was as an autosomal recessive trait.

Glutamate and gamma-aminobutyric acid neurotransmitter systems in the acute phase of maple syrup urine disease and citrullinemia encephalopathies in newborn calves

Cerebral cortex tissue was obtained at autopsy from neonatal Poll Hereford calves with clinically confirmed maple syrup urine disease (MSUD), neonatal Holstein-Friesian calves with clinically confirmed citrullinemia, and matched controls. From this, synaptosomes were prepared for studies of neurotransmitter amino acid uptake and stimulus-induced release, and synaptic plasma membranes were obtained for studies of associated postsynaptic receptor binding sites. As well as having abnormal brain tissue concentrations of the pathognomic plasma amino acids (markedly increased levels of the branched-chain compounds valine, isoleucine, and leucine in MSUD; marked elevation of citrulline levels in citrullinemia), both groups of diseased animals showed reduced brain tissue concentrations of each of the transmitter amino acids glutamate, aspartate, and gamma-aminobutyric acid (GABA). Nontransmitter amino acids were generally unaffected in either disease. Citrullinemic calves showed a marked increase in brain glutamine concentration; in calves with MSUD, the glutamine concentration was raised, but to a much lesser extent. The Na(+)-dependent synaptosomal uptake of both glutamate and GABA was markedly reduced (to less than 50% of control values in both cases) in citrullinemic calves but was unaltered in calves with MSUD. Whereas synaptosomes from normal calves showed the expected stimulus-coupled release of transmitter amino acids, especially glutamate and aspartate, and no response to stimulus of nontransmitter amino acids, there was no increased release of transmitter amino acids in response to depolarization in synaptosomes from citrullinemic calves.(ABSTRACT TRUNCATED AT 250 WORDS)

β-Mannosidosis in a Salem calf: A new storage disease of cattle

A storage disease characterised by widespread vacuolation of cells throughout the body was diagnosed in a newborn calf of the Salers breed. Extraction and analyses of water soluble material showed that the storage material was oligosaccharide in nature and was probably derived from the core region of the heterosaccharide moiety of glycoproteins. Glycosidase analyses showed that the disease was due to a deficiency of acidic beta-mannosidase.

Phenotypic variation in bovine alpha-mannosidosis

Breeding experiments were conducted in 1984, 1985 and 1986, using Angus and Galloway bulls and cows that were obligatory heterozygotes for alpha-mannosidosis. Sixty-nine calves were born in the herd of which 16 were diagnosed as cases of alpha-mannosidosis. The clinical and pathological findings in eight Angus cross Angus, four Galloway cross Angus, and four Galloway cross Galloway calves affected with alpha-mannosidosis are reported. Thirteen calves displayed neurological signs in the early neonatal period. Three Galloway cross Galloway calves were stillborn. The severity of disease caused death or necessitated euthanasia within the first week of life of 10 affected calves. Three Angus cross Angus calves survived 40, 80 and 210 days. These findings illustrate significant variation in the phenotypic expression of alpha-mannosidosis both within and between the breeds.

Bovine citrullinaemia: a clinical, pathological, biochemical and genetic study

Calves affected with citrullinaemia are clinically normal immediately after birth. In the majority of calves the clinical course of the disease was similar. Within 24 hours of birth they become depressed; then within 3 to 4 days were observed to wander aimlessly or stand with their head pressed against a wall or fence. By day 4 to 5 they become recumbent, developed convulsions, followed by collapse and death. Oedema of the cerebral cortex is a consistent histological lesion. Citrulline concentration in blood, cerebrospinal fluid, eye fluid and cerebral tissue is greatly elevated. Information gathered from pedigrees of affected calves indicate that the defect is widely disseminated throughout the Australian Friesian population.

Maple syrup urine disease (branched chain ketoaciduria)

Images

Premature translation termination of the pre-E1 alpha subunit of the branched chain alpha-ketoacid dehydrogenase as a cause of maple syrup urine disease in Polled Hereford calves

Maple syrup urine disease in man and cattle is an inborn metabolic error caused by the deficiency of the branched chain alpha-ketoacid dehydrogenase. We have studied the molecular basis of the disease in Polled Hereford calves. The E1 component of branched chain alpha-ketoacid dehydrogenase was virtually undetectable by Western blot analysis of fibroblasts from an affected calf. Northern blot analysis failed to detect the E1 alpha mRNA species in the fibroblasts. Nevertheless, it was readily demonstrated by reverse transcription of RNA followed by polymerase chain reaction that the mRNA for the E1 alpha subunit was present in the cells, albeit at very low concentrations. Sequencing of the polymerase chain reaction-generated cDNA for the entire coding region of the E1 alpha subunit revealed a single base substitution at codon -6 (CAG to TAG). This mutation introduces a stop codon in the leader peptide of the E1 alpha subunit, resulting in the premature termination of translation. The mutation was verified by hybridization of the amplified cDNA fragments from two affected calves with allele-specific oligonucleotides. This finding explains the pathogenesis of maple syrup urine disease in this breed of cattle, which provides the only known animal model for the human disease. In addition, the results provide evidence for the effect of premature translation termination on reducing the steady-state mRNA level and the dependence of E1 beta protein stability on the co-expression of the E1 alpha.

Animal model of human disease. Citrullinemia (argininosuccinate synthetase deficiency)

Images

Molecular definition of bovine argininosuccinate synthetase deficiency

Citrullinemia is an inborn error of metabolism due to deficiency of the urea cycle enzyme, argininosuccinate synthetase [L-citrulline:L-aspartate ligase (AMP-forming), EC 6.3.4.5]. The disease was first described in humans but was recently reported in dairy cattle in Australia. Here we report the nucleotide sequence of the normal bovine cDNA for argininosuccinate synthetase and the mutation present in animals with citrullinemia. Analysis of DNA from affected animals by Southern blotting did not readily identify the mutation in the bovine gene. RNA (Northern) blotting revealed a major reduction in the steady-state amount of mRNA in the liver of affected animals to less than 5% of controls. The bovine cDNA was cloned and sequenced and revealed 96% identity with the deduced human sequence at the amino acid level. Starting with mutant bovine liver, the mRNA was reverse-transcribed; the cDNA product was amplified with the polymerase chain reaction, cloned, and sequenced. The sequence revealed a C----T transition converting arginine-86 (CGA) to a nonsense codon (TGA). A second C----T transition represented a polymorphism in proline-175 (CCC----CCT). The mutation and the polymorphism were confirmed by amplification of genomic DNA and demonstration with restriction endonuclease enzymes of both the loss of an Ava II site in DNA from mutant animals at codon 86 and the presence or absence of a Dde I site at codon 175. The loss of the Ava II site can be used for rapid, economical, nonradioactive detection of heterozygotes for bovine citrullinemia.

Neurological disease associated with degenerative axonopathy of neonatal Holstein-Friesian calves

The clinical and pathological features of 19 neonatal Holstein-Friesian calves affected with moderate to severe neurological disease are presented. Most calves were recumbent from birth, and many developed variable neurological signs including hyperaesthesia or depression, limb extension, head tremor, nystagmus, apparent blindness, and opisthotonos when stimulated. Consistent lesions of moderate to severe, diffuse, axonal swelling and loss, with Wallerian-type degeneration and myelin depletion in the spinal cord and brainstem, and occasionally in the midbrain and peripheral nerve roots, were observed. The lesions indicated a pre-natal insult affecting mainly motor areas of the foetal neuraxis, however the aetiology of the disorder remains undetermined. It is suggested that the calves may have been affected by a hitherto unrecognised disease entity for which we propose the term, degenerative axonopathy.

Maple syrup urine disease in calves: a clinical, pathological and biochemical study

The clinical, pathological and biochemical findings of a study of 30 Poll Hereford, Hereford, Poll Hereford cross or Hereford cross calves affected with branched chain ketoacid dehydrogenase (BCKAD) complex deficiency or maple syrup urine disease (MSUD) are presented. In breeding studies, 6 of 21 calves from obligate heterozygote matings were affected with MSUD, suggesting the disease is inherited in an autosomal recessive manner. Calves were clinically affected from birth, but there were variations in the subsequent course of progressive deterioration of central nervous system function. Concentrations of the branched chain amino acids and keto acids were elevated in pre-suckle plasma and cerebellar water content was higher in affected calves. Activity of BCKAD complex was minimal in fibroblasts cultured from an affected calf. Spongiform encephalopathy and elevated ratios of the branched to straight chain amino acids in formalin fixed cerebral tissue were found in a stillborn foetus and a 3-month-old Hereford calf. These findings suggest the disease occurs prenatally and that a delayed form may exist.

Deficit of spinal cord glycine/strychnine receptors in inherited myoclonus of Poll Hereford calves

Inherited myoclonus of Poll Hereford calves is characterized by hyperesthesia and myoclonic jerks of the skeletal musculature, which occur spontaneously and in response to sensory stimuli. The disease shows autosomal recessive inheritance, and significant proportions of the Poll Hereford herds in many countries are thought to be carriers of the mutant gene. Studies revealed a specific and marked (90 to 95 percent) deficit in [3H]strychnine binding sites in spinal cord membranes from myoclonic animals compared to controls, reflecting a loss of, or defect in, glycine/strychnine receptors. Spinal cord synaptosomes prepared from affected animals showed a significantly increased ability to accumulate [3H]glycine, indicating an increased capacity of the high-affinity neuronal uptake system for glycine. In contrast, stimulus-induced glycine release and spinal cord glycine concentrations were unaltered.

Neurovisceral ceroid-lipofuscinosis in blind Devon cattle

Ten Devon cattle from a single property were affected with blindness from 14 months of age. Severe retinal degeneration progressing to atrophy was associated with widespread intracellular accumulation of pigment in the retinal ganglion cells, central nervous system and major organs. The pigment was consistent with ceroid-lipofuscin granules on histological, histochemical and ultrastructural examination. Although a familial relationship existed between affected individuals, a pattern of inheritance could not be established by examination of available breeding records. The disease is compared to similar disorders reported in man and other species.

Ultrastructural findings in citrullinaemia in Holstein-Friesian calves

Ultrastructural findings in the brains and livers of four calves affected with citrullinaemia due to a hereditary deficiency of the urea cycle enzyme arginosuccinate synthetase are described. The calves were affected in the 1st week of life with severe neurological disease characterised by depression, head pressing, stupor, convulsions and coma, accompanied by marked elevation of plasma citrulline and increasing plasma ammonia levels. Lesions included mild to moderate diffuse astroglial oedema in the cerebrocortical grey matter, and mild to severe hepatocellular hydropic change. The onset of the severe neurological signs was correlated with increasing levels of plasma ammonia, and the cerebral lesions were considered consistent with a bovine hyperammonaemic encephalopathy.

Enzyme replacement in nervous tissue after allogeneic bone-marrow transplantation for fucosidosis in dogs

Bone-marrow transplantation after total lymphoid irradiation in an alpha-L-fucosidase-deficient dog raised the enzyme activity in both visceral and neural tissues with consequent reduction in the severity of storage lesions. These results offer hope that early marrow transplantation may prevent the development of disease in neurovisceral storage disorders.