A high-throughput method for unbiased quantitation and categorisation of nuclear morphology

The physical arrangement of chromatin in the nucleus is cell type and species specific. This is particularly evident in sperm, in which most of the cytoplasm has been lost; the shape of the nucleus reflects the shape of the cell. Mice have distinctive falciform (‘hook shaped’) sperm heads and nuclei. Quantification of the differences in shape variation between mouse species and lines often relies on manual measurement and classification that leads to subjective results, making comparisons within and between samples difficult. We have developed an analysis program for assessing the morphology of asymmetric nuclei, and characterised the sperm of mice from a range of inbred, outbred and wild-derived mouse lines. We find that laboratory lines have elevated sperm shape variability both within and between samples in comparison to wild-derived inbred lines, and that sperm shape in the F1 offspring of CBA and C57Bl6J lines is subtly affected by the direction of the cross. Hierarchical clustering can distinguish distinct sperm shapes with greater efficiency and reproducibility than even experienced manual assessors. We quantified the range of morphological defects in the inbred BALB/c line, demonstrating we can identify different morphological subgroups. This approach has applications for studies of sperm development, infertility and toxicology.