Worm Breeder's Gazette 7(1): 74

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A Recessive Mutation Affecting Nucleolar Size

E. Hedgecock, N. Thomson

An EMS induced mutant (e1865) on linkage group III has exceptionally 
large nucleoli.  For example, neuronal nucleoli are enlarged about ten-
fold in volume.  (The relative increase is smaller in cells which 
normally have a large nucleolar/nuclear size ratio.) All cell types, 
including germ cells and embryonic cells, are affected by the mutation.
Nuclear size is unaffected.  We do not think the mutation is simply 
a germline increase in rDNA since it is recessive, not semidominant.  
Mutant nuclei have either one large nucleolus or two smaller nucleoli, 
never more, suggesting that there are only two nucleolar organizers (
one per haploid genome) as in wildtype.  Homozygous animals are 
relatively healthy and fertile.  Since the mutation can be scored in 
all cells (with practice), it may be a useful, nondestructive marker 
for genetic mosaicism.  (We have not yet examined embryos for maternal 
effects.) The map order is dpy-17(14/23)e1865(9/23)unc-32.  Mutant 
nucleoli appear fairly normal, albeit large, in electron micrographs.  
We (with Maria Salvato) hope to learn whether rRNA synthesis, ribosome 
assembly and export are normal.