Segmental axonopathy of Merino sheep in New Zealand

Abstract

AIM: To investigate an axonopathy of Merino sheep that caused progressive hindlimb ataxia and slight to moderate paresis, with the purpose of understanding its pathogenesis.

METHODS: Tissues were fixed in buffered paraformaldehyde or paraformaldehyde and glutaraldehyde, processed into wax and epoxy resin, respectively, and examined by light and electron microscopy. Fresh frozen spinal cord and trigeminal nerve roots were subjected to homogenisation, centrifugation and two-dimensional electrophoresis. Selected protein spots were identified using matrix-assisted laser desorption ionisation (MALDI) mass spectrometry.

RESULTS. By light microscopy, there were large pale foamy spheroidal axonal swellings affecting peripheral as well as central axons. By electron microscopy, these were shown to contain many membrane-bound vesicles. The main abnormalities in expressed proteins involved cytoskeletal elements and myosin heavy chain, the latter interpreted as associated with the molecular motor myosin Va.

CONCLUSIONS: The disorder is the same as that described in Merinos in Australia as segmental axonopathy, and believed to have an inherited aetiology. The lesions and protein changes indicate abnormalities of the cytoskeleton, its relationship with the myelin sheath, and myosin Va molecular motor. The consequence appears to be abnormal axonal transport and inability to maintain the integrity of axons and their myelin sheaths.

KEY WORDS:

• Axonopathy
• cytoskeleton
• neurofilaments
• myosin Va
• spectrin
• myelin

Acknowledgements

We wish to acknowledge the help and cooperation of the sheep breeders concerned; the help of Mrs Pat Davey for special histo-chemical stains; and Messrs Aaron Hicks, Raymond Bennett and Douglas Hopcroft for assistance with preparation of tissues for electron microscopy and printing of electron micrographs.

Notes

¹MG Collett, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand

²KH Parton, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand