Myosin VI is required for asymmetric segregation of cellular components during C. elegans spermatogenesis

BACKGROUND

The asymmetric division of cells and unequal allocation of cell contents is essential for correct development. This process of active segregation is poorly understood but in many instances has been shown to depend on the cytoskeleton. Motor proteins moving along actin filaments and microtubules are logical candidates to provide the motive force for asymmetric sorting of cell contents. The role of myosins in such processes has been suggested, but few examples of their involvement are known.

RESULTS

Analysis of a Caenorhabditis elegans class VI myosin deletion mutant reveals a role for this motor protein in the segregation of cell components during spermatogenesis. Mutant spermatocytes cannot efficiently deliver mitochondria and endoplasmic reticulum/Golgi-derived fibrous-body membranous organelle complexes to budding spermatids, and fail to remove actin filaments and microtubules from the spermatids. The segregation defects are not due to a global sorting failure as nuclear inheritance is unaffected.

CONCLUSIONS

C. elegans myosin VI has an important role in the unequal partitioning of both organelles and cytoskeletal components, a novel role for this class of motor protein.

Dextrose administration increases sensory/motor impairment and paraplegia after infrarenal aortic occlusion in the rabbit

Spinal ischemia with resultant cord infarction is a catastrophic complication of surgical procedures involving the thoracoabdominal aorta. A rabbit spinal ischemia model was used to test if glucose administration would increase neurologic deficit of the lower extremity. Rabbits (2 to 3 kg), anesthesized with halothane, had a snare occluder placed around the aorta just below the left renal artery. After a 2-hour recovery, the aorta was occluded for 15 minutes. Before occlusion animals received an intraperitoneal injection of isotonic glucose (2 gm/kg; n = 11), isotonic mannitol (2 gm/kg; n = 3), or an equal volume of saline solution (n = 11). Four sham-operated animals received glucose and an identical surgical procedure, but the aorta was not occluded. Average blood glucose level at the time of occlusion for the glucose group was 249 +/- 15 versus 156 +/- 6 for the control group (p less than 0.01). At 1, 4, 18, and 24 hours, a neurologic impairment score (1 = normal, 2 = partial impairment, 3 = complete impairment) was assigned. At 4, 18, and 24 hours, the glucose group had significantly greater neurologic impairment than did control groups (p less than 0.02). Glucose administration had an adverse effect in a controlled and highly reproducible model of spinal cord ischemia. Exogenous glucose administration should potentially be avoided during complex aortic reconstruction.