Neutrophils are the most abundant immune cell type in the human peripheral blood. They are also famously polymorphonuclear, meaning they possess non-spherical nuclei, generally manifesting as nuclei segmented into multiple lobes. While this lobed morphology was identified over 100 years ago, it is still not known why neutrophils lobulate their nuclei. Furthermore, it is unclear how neutrophils distribute their chromosomes within the lobes. Some studies have suggested that autosomes are randomly distributed across lobes, while others show non-random distribution.
Here we use chromosome paint to comprehensively resolve this conflict. Chromosome paint uses tiled fluorescent probes to identify the position and three-dimensional characteristics of all chromosomes within individual nuclei using high resolution imaging.
We analysed hundreds of neutrophil nuclei using our novel analysis pipeline. By comparing each biological image to a computationally generated image that randomly shuffles the chromosomes from each image, we show for the first time that chromosome distribution within both human and mouse neutrophil lobes is random. Furthermore, we show that, like immune cells with spherical nuclei, the radial distribution of neutrophil chromosomes within lobes in non-random, with larger chromosomes more frequently positioned near the nuclear lamina.
This suggests that neutrophil lobing is a process uncoupled from genome/chromosome organisation and that the chromosomes are relatively indifferent to the spatial restriction imposed by lobulation.