Asymmetric vimentin distribution in human spermatozoa

The subject of the study was vimentin distribution in spermatozoa from human ejaculates by immunofluorescence and immunogold electron microscopy. In accordance with earlier reports, vimentin was found in the sperm head and was localized mainly in the equatorial segment region. However, electron microscopic observations revealed an additional intriguing detail: vimentin-associated gold granules showed asymmetric distribution. This asymmetry tended to be more pronounced in heads with defects such as cytoplasmic droplets. Abnormal cells also had positive reaction for vimentin in the neck and the proximal midpiece, but in these domains gold granule distribution was apparently uniform. These findings seem to support the hypothesis that the surfaces of the mammalian sperm head are functionally non-equivalent, although morphological basis for such a phenomenon is evident only in rodents. It is also interesting that asymmetry in vimentin distribution correlates with distinct types of sperm structural defects.