Yasuo Moritomo

Positional cloning of the gene LIMBIN responsible for bovine chondrodysplastic dwarfism

Chondrodysplastic dwarfism in Japanese brown cattle is an autosomal recessive disorder characterized by short limbs. Previously, we mapped the locus responsible for the disease on the distal end of bovine chromosome 6. Here, we narrowed the critical region to ≈2 cM by using linkage analysis, constructed a BAC and YAC contig covering this region, and identified a gene, LIMBIN (LBN), that possessed disease-specific mutations in the affected calves. One mutation was a single nucleotide substitution leading to an activation of a cryptic splicing donor site and the other was a one-base deletion resulting in a frameshift mutation. Strong expression of the Lbn gene was observed in limb buds of developing mouse embryos and in proliferating chondrocytes and bone-forming osteoblasts in long bones. These findings indicate that LBN is responsible for bovine chondrodysplastic dwarfism and has a critical role in a skeletal development.

Localization of a locus responsible for the bovine chondrodysplastic dwarfism (bcd) on chromosome 6.

A hereditary chondrodysplastic dwarfism caused by an autosomal recessive gene has been reported in a population of Japanese Brown cattle. Affected calves show an insufficiency of endochondral ossification at the long bones of the limbs. In the present study, we mapped the locus responsible for the disease (bcd) by linkage analysis, using microsatellite markers and a single paternal half-sib pedigree obtained from commercial herds. Linkage analysis revealed a significant linkage between the bcd locus and marker loci on the distal region of bovine Chromosome (Chr) 6. The bcd locus was mapped in the interval between microsatellite markers BM9257 and BP7 or BMS511 with a recombination fraction of 0.05 and 0.06, and a lod score of 8.6 and 10.1, respectively. A comparison of genetic maps between bovine Chr 6 and human Chr 4 or mouse Chr 5 indicates possible candidate genes including FGFR3 and BMP3 genes, which are responsible for human chondrodysplasias and associated with bone morphogenesis, respectively.

A missense mutation (p.Leu2153His) of the factor VIII gene causes cattle haemophilia A.

Two cases of hereditary bleeding disorder diagnosed as haemophilia A were recently observed in Japanese Brown cattle. We sequenced the entire coding region of the factor VIII gene of the affected animals to find a causative mutation. A nucleotide substitution of T to A resulting in an amino acid substitution of leucine to histidine (p.Leu2153His) was identified in a highly conserved residue in the C1 domain of factor VIII. Genotyping of 254 normal animals including the pedigree of the affected animals and randomly sampled animals of different breeds confirmed that the substitution is the causative mutation of cattle haemophilia A.

Segmental spinal dysgenesis with caudal agenesis in a Holstein calf

A rare complex dysraphic malformation, comprising segmental spinal dysgenesis with caudal agenesis, was found in a Holstein calf that was unable to stand and was slightly short at the lumbosacral spine with taillessness. The thoracolumbar and sacrococcygeal regions of the midline axial segments showed severe deformities. In the spinal cord, the thoracolumbar region showed severe constriction with myelodysplastic changes, and the sacrococcygeal region showed dorsoventral separation with connection to a neural mass. In the spine, vertebral anomalies according to the degree of the segmentation error were confirmed. The cervical and thoracic segments also showed milder dysraphic changes. These changes suggest a multisegmental causal insult impairing the early embryonic notochord. This represents the first bovine case definitively confirmed morphologically.

Right Ductus Arteriosus in a Calf

Fallots tetralogy with right ductus arteriosus was detected in a Holstein calf. The right ductus arteriosus measured approximately 6mm in outside diameter. It arose from the pulmonary trunk immediately before the bifurcation into the right and left pulmonary arteries. It ran anteriorly meandering on the right side of the aortic arch and drained into the brachiocephalic trunk immediately before the ramification of the left subclavian artery. The aortic arch was normally formed by the left fourth aortic arch. This ductal anomaly was considered to have developed at the early formative stage of the circulatory system as a rudiment of the distal portion of the right sixth aortic arch.