Nucleus fills the whole cell - (Mar/05/2012 )

Hi All,
I have a question about an interesting phenomenon I have seen in Drosophila.
I am dealing with a certain cell type in drosophila. There is no clear functional report about those cells, but they do express some marker proteins of mammalian podocyte. They can uptake GFP proteins from other tissue. People think they might be drosophila kidney, but I dont believe. I think they might be similar to macrophage.
Most interestingly, lately I found that, in those cells from the aged adult flies (only from aged fly, but not from young fly), the whole cell is filled with nucleus (by DAPI staining). First thought is they might undergo apoptosis. However, I did TUNEL assay on those cells and no positive staining. Secondly I did BRDU staining, also no positive staining.
So my question is, has anybody seen the similar phenotype in mammals? what cell type they might be?
Thanks.
Genomy

Have a look for information on polytene chromosomes - they may be what you are seeing and are usually found in secretory cells in dipterans.

Thanks bob1.
But how do u explain the BRDU staining? I have been feeding those flies for 1 week BRDU. They dont have any BRDU signal.

How about senescence?