Intranuclear crystalline inclusions in spermatozoa ofLumbricus terrestris

Summary In the nuclei of atypical spermatids ofLumbricus terrestris granular or filamentous inclusions are surrounded by dense chromatin. Aggregation and condensation of chromatin in nuclei during spermatid differentiation coincide with increase in density, granularity, and the subsequent crystallization of the intranuclear inclusion. In mature spermatozoa, the crystalline inclusion displaying an irregular shape is composed of parallel repeating units measuring 50–80 Å. The subunits sometimes possess a clear central cavity.Atypical spermatozoa, possessing inclusions that distort their normally cylindrical shape, possess typical acrosomes, middle pieces, and flagella. Spermatozoa bearing intranuclear crystals are rarely observed in the seminal receptacles ofLumbricus.These intranuclear inclusions probably represent proteinaceous material that is not eliminated during nuclear differentiation. Their sole existence in the nuclei of spermatozoa, their transformation into crystalline structures during spermiogenesis, and their similarity to crystals in virus infected plant and animal cells suggest a viral origin.Supported by a training grant (GM-00582-07) from the Public Health Service.