An EHPB1L1 Nonsense Mutation Associated with Congenital Dyserythropoietic Anemia and Polymyopathy in Labrador Retriever Littermates

Molecular mechanisms of polarized transport to the apical plasma membrane

Cell polarity is essential for cellular function. Directional transport within a cell is called polarized transport, and it plays an important role in cell polarity. In this review, we will introduce the molecular mechanisms of polarized transport, particularly apical transport, and its physiological importance.

Whole Animal Genome Sequencing: user-friendly, rapid, containerized pipelines for processing, variant discovery, and annotation of short-read whole genome sequencing data

Advancements in massively parallel short-read sequencing technologies and the associated decreasing costs have led to large and diverse variant discovery efforts across species. However, processing high-throughput short-read sequencing data can be challenging with potential pitfalls and bioinformatics bottlenecks in generating reproducible results. Although a number of pipelines exist that address these challenges, these are often geared toward human or traditional model organism species and can be difficult to configure across institutions. Whole Animal Genome Sequencing (WAGS) is an open-source set of user-friendly, containerized pipelines designed to simplify the process of identifying germline short (SNP and indel) and structural variants (SVs) geared toward the veterinary community but adaptable to any species with a suitable reference genome. We present a description of the pipelines [adapted from the best practices of the Genome Analysis Toolkit (GATK)], along with benchmarking data from both the preprocessing and joint genotyping steps, consistent with a typical user workflow.

Canine models of Charcot-Marie-Tooth: MTMR2, MPZ, and SH3TC2 variants in golden retrievers with congenital hypomyelinating polyneuropathy

Congenital hypomyelinating polyneuropathy (HPN) restricted to the peripheral nervous system was reported in 1989 in two Golden Retriever (GR) littermates. Recently, four additional cases of congenital HPN in young, unrelated GRs were diagnosed via neurological examination, electrodiagnostic evaluation, and peripheral nerve pathology. Whole-genome sequencing was performed on all four GRs, and variants from each dog were compared to variants found across >1,000 other dogs, all presumably unaffected with HPN. Likely causative variants were identified for each HPN-affected GR. Two cases shared a homozygous splice donor site variant in MTMR2, with a stop codon introduced within six codons following the inclusion of the intron. One case had a heterozygous MPZ isoleucine to threonine substitution. The last case had a homozygous SH3TC2 nonsense variant predicted to truncate approximately one-half of the protein. Haplotype analysis using 524 GR established the novelty of the identified variants. Each variant occurs within genes that are associated with the human Charcot-Marie-Tooth (CMT) group of heterogeneous diseases, affecting the peripheral nervous system. Testing a large GR population (n = >200) did not identify any dogs with these variants. Although these variants are rare within the general GR population, breeders should be cautious to avoid propagating these alleles.

EHBP1L1, an apicobasal polarity regulator, is critical for nuclear polarization during enucleation of erythroblasts

Cell polarity, the asymmetric distribution of proteins and organelles, is permanently or transiently established in various cell types and plays an important role in many physiological events. epidermal growth factor receptor substrate 15 homology domain-binding protein 1-like 1 (EHBP1L1) is an adapter protein that is localized on recycling endosomes and regulates apical-directed transport in polarized epithelial cells. However, the role of EHBP1L1 in nonepithelial cells, remains unknown. Here, Ehbp1l1-/- mice showed impaired erythroblast enucleation. Further analyses showed that nuclear polarization before enucleation was impaired in Ehbp1l1-/- erythroblasts. It was also revealed that EHBP1L1 interactors Rab10, Bin1, and dynamin were involved in erythroblast enucleation. In addition, Ehbp1l1-/- erythrocytes exhibited stomatocytic morphology and dehydration. These defects in erythroid cells culminated in early postnatal anemic lethality in Ehbp1l1-/- mice. Moreover, we found the mislocalization of nuclei and mitochondria in the skeletal muscle cells of Ehbp1l1-/- mice, as observed in patients with centronuclear myopathy with genetic mutations in Bin1 or dynamin 2. Taken together, our findings indicate that the Rab8/10-EHBP1L1-Bin1-dynamin axis plays an important role in multiple cell polarity systems in epithelial and nonepithelial cells.

EHBP1L1 Frameshift Deletion in English Springer Spaniel Dogs with Dyserythropoietic Anemia and Myopathy Syndrome (DAMS) or Neonatal Losses

Hereditary myopathies are well documented in dogs, whereas hereditary dyserythropoietic anemias are rarely seen. The aim of this study was to further characterize the clinical and clinicopathological features of and to identify the causative genetic variant for a dyserythropoietic anemia and myopathy syndrome (DAMS) in English springer spaniel dogs (ESSPs). Twenty-six ESSPs, including five dogs with DAMS and two puppies that died perinatally, were studied. Progressive weakness, muscle atrophy—particularly of the temporal and pelvic muscles—trismus, dysphagia, and regurgitation due to megaesophagus were observed at all ages. Affected dogs had a non-regenerative, microcytic hypochromic anemia with metarubricytosis, target cells, and acanthocytes. Marked erythroid hyperplasia and dyserythropoiesis with non-orderly maturation of erythrocytes and inappropriate microcytic metarubricytosis were present. Muscle biopsies showed centralized nuclei, central pallor, lipocyte infiltrates, and fibrosis, which was consistent with centronuclear myopathy. The genome sequencing of two affected dogs was compared to 782 genomes of different canine breeds. A homozygous frameshift single-base deletion in EHBP1L1 was identified; this gene was not previously associated with DAMS. Pedigree analysis confirmed that the affected ESSPs were related. Variant genotyping showed appropriate complete segregation in the family, which was consistent with an autosomal recessive mode of inheritance. This study expands the known genotype–phenotype correlation of EHBP1L1 and the list of potential causative genes in dyserythropoietic anemias and myopathies in humans. EHBP1L1 deficiency was previously reported as perinatally lethal in humans and knockout mice. Our findings enable the genetic testing of ESSP dogs for early diagnosis and disease prevention through targeted breeding strategies.