The ultrastructural study of ribosomes in photoreceptor inner segments of the pcd cerebellar mutant mouse.

Ultrastructural changes in the distribution of free ribosomes in photoreceptor inner segments in relation to photoreceptor degeneration in Purkinje cell degeneration (pcd) were studied in mutant mice reared under cyclic light and sacrificed at 30 and 120 postnatal days. On postnatal day 30, some photoreceptors appeared to be normal whereas others had degenerated to varying degrees with numerous spherules in the extracellular space surrounding degenerating inner segments. By postnatal day 120, retinal degeneration had progressed with a marked loss of photoreceptors. The distribution of free ribosomes in the mutant inner segments was random, clustered, or uniform. This was distinct from normal control retinas in which random distribution predominated. Markedly degenerated inner segments contained sparse ribosomes which coalesced in small aggregates. These changes in ribosome distribution seemed to be associated with the extent of photoreceptor degeneration. The significance of these changes in ribosome distribution, in particular clustered distribution, is discussed together with our previous findings.