TEM nuclear anatomy

Originally posted on WormAtlas by “tom donndelinger”, February 01, 2005

transmission EM – I would need details of variation features of nuclei in various tissues.

tom donndelinger

Originally posted on WormAtlas by “hall”, February 08, 2005

Well, that is a pretty broad topic; I’m intending to summarize aspects of nuclear morphology eventually on WormAtlas as a subsection, but we’re not ready just yet.

Nuclear appearance changes during the cell cycle, of course, but TEM is a rather laborious way to follow this. I have not tried, but I think that others have done so for early embryos, especially to look at stages in mitosis.

Nuclei vary from tissue to tissue in size. Nuclei in smaller cells tend to be smaller and compact (no surprise), but should still show the same basic features: a nucleolus, dark patches of heterochromatin surrounded by lighter areas of euchromatin. Nuclear pores are present but may be difficult to see except at high magnification in well fixed specimens. Nuclear pores are much easier to see by freeze fracture of the whole animal. By this method it is evident that nuclear pores occur in high numbers, spread evenly over the surface of the nuclear envelope.

Larger cells and cell syncytia tend to have rather large nuclei, based upon the process of endoreduplication (Hedgecock and White, 1985) which loads them with more sets of chromosomes per nucleus. Thus muscle cells, hypodermis and intestine have very large nuclei. In fact in the intestine, the nuclei divide so that adult cells have two very large nuclei per cell. Presumably this process helps larger cells to produce relatively more RNAs and protein as cellular events demand.

With a little searching in the WormAtlas Handbook and the Slideable Worm, you will see examples of many of these features. If there is some particular cell type of interest, let me know privately and we can supply those images to you.

David H Hall