Molecular Investigations on Spastic Paresis and Other Inheritable Bovine Diseases
by Frederik Krull
Date of Examination:2024-10-08
Date of issue:2024-10-30
Advisor:Prof. Dr. Dr. Bertram Brenig
Referee:Prof. Dr. Dr. Bertram Brenig
Referee:Prof. Dr. Jens Tetens
Referee:Prof. Dr. Tosso Leeb
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Abstract
English
Genetic mutations often cause serious diseases associated with severe animal suffering. Today, molecular methods enable efficient research and prevent spreading of disease alleles in cattle populations. The main objective of this thesis was to investigate molecular mechanisms of certain bovine diseases and to identify associated genetic variants. This helps to understand underlying cellular mechanisms in these diseases and to regulate disease prevalences in the population. Chapter 1 provides a general overview of the investigated bovine diseases, i.e. small calf syndrome, X-linked Hypohydrotic ectodermal dysplasia (XLHED) and bovine spastic Paresis (BSP). This also covers known genetic mechanisms. It thereby presents findings from prior investigations. Chapter 2 covers "Small Calf Syndrome" in more detail, a congenital disorder of glycosylation that was reported in cattle from New Zealand. Small calf syndrome is a monogenic disease and arises from a splice acceptor SNP in exon 16 of GALNT2 (NC_037355.1:g.1312334G>A). A genetic test for this variant has been developed. This demonstrated absence of the allele in the German cattle population. Attempts were made to associate markers from a common bovine microarray with this variant for haplotype testing. In Chapter 3, a case report of X-linked Hypohydrotic ectodermal dysplasia (HED) in a Limousin male calf is discussed. The disease occurred sporadically within one single family. The causative variant, rs439722471, was identified by a candidate gene approach using Sanger sequencing. This variant was within the TNF-like domain of ectodysplasin A. The mother and grandmother of the affected bull were identified as heterozygous carriers. The variant has been tested in additional 2016 individuals and had not been detected. So it is most likely the disease causing mutation. HED shows a pathognomonic symptom complex of hypotrichosis, hypodontia and hyperhidrosis. Tissues of the affected animal were examined for these symptoms by histology and computed tomography. In Chapter 4, a cohort of 46 cases of bovine spastic paresis (BSP) and controls were genotyped on a microarray and genome-wide association testing was used to associate a genomic region on chromosome 15 with BSP. Subsequent whole genome sequencing of affected parent- offspring trios highlighted a single variant in the associated region, i.e. NC_037342.1:g.78135822_78135823insC. This variant is within LOC100848076, an annotated transcript. Its expression in bovine brain tissue was demonstrated by RTPCR. LOC100848076 was predicted as G protein-coupled receptor by homology modeling. Protein network analysis indicated interactions with relevant genes for neuromuscular diseases. However, since the above-mentioned variant was very common in the population, it cannot monogenetically cause BSP. In Chapter 5, BSP was examined by transcriptome analysis and histological methods applied on the brainstem, spinal cord and musculature to investigate the pathogenesis and anatomical position of relevant pathologies. We identified that all examined tissues express OOSP2 in contrast to healthy animals. In addition, reduced expression of inhibitory neurotransmitters in brainstem tissue was noted. Histological abnormalities were only identified in brainstem tissue, whereas inflammatory infiltrates of microglia and T lymphocytes were detected in case and control cohorts. However, these occurred significantly more often in individuals suffering from BSP. These pathological changes characteristically occur in combination with viral infections in the central nervous system. Thus, the disease causing pathologies can be localized in the brainstem and identified as autoimmune or neurodegenerative processes with a possible infectious origin. This targets inhibitory neurons in the brainstem, causing the typical symptoms of motor neuron disease. In Chapter 6, BSP and HED are discussed in more detail. For HED, the identified variant in Limousin cattle is related to the previously known variants. For BSP, etiological hypotheses are listed and methods are suggested to investigate them.
Keywords: Bovine Spastic Paresis; Hypohidrotic Ectodermal Dysplasia; Next Generation Sequencing; Genome-wide Association Study; Polymerase Chain Reaction; Inherited Bovine Disease