Why do neutrophil granulocytes have segmented nuclei?

[Jens]

 

I currently see the following explanation (see below). Any better ideas? Any major issues with the explanation? (of course this is at least partially speculation. I just want to get the most likely explanation -- not a proof )

 

 

Input:

• Recently it was published that the chromosomes in animals have a specific order in space in the nucleus. This means dependent on the cell type certain chromosomes always have the same neighbors within the nucleus. (Segmented nuclei obviously fix this order in a very drastic way.)
• Recently it was also published that actually the vast majority of the so called junk DNA is transcribed (but at low copy number, and of course not translated). Those long transcribed RNAs have shown to have regulatory effects in complex gene activation processes including timing effects (the length of the RNA matters and not so much which bases it contains, the distance in space also might matter in the same way).
• Malignant tumor cells often (typically?) have multiple chromosome disorders (split, fusion, parts of one chromosome moved to another, trisomy, …). So it looks that destroying this order in space actually matters.
• Neutrophil granulocytes are the most common white blood cells and kill microbes (bacteria, viruses and fungi). Neutrophil granulocytes act as macrophages and produce a lot of reactive oxygen species of multiple kinds, which all can diffuse through membranes and cause a lot of damage also to DNA.
• Neutrophil granulocytes do not divide any more after maturation. Patients with lack of segmented nuclei have a reduced immune response (and not more cancer).

Explanation:

The segmentation ensures that the natural needed order in space of the chromosomes is conserved, even though the high amount of reactive oxygen species causes a lot of covalent breaks and rearrangements of the DNA in active neutrophil granulocytes. The large fragments of DNA are trapped physically within the segment. This keeps the granulocytes longer function normally and thereby active in the immune response.