Worm Breeder's Gazette 11(4): 33
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.
The genome of Panagrellus redivivus contains two distinct satellites, dubbed E155 and E167. They have a reiteration frequency of nearly 30, 000 copies per haploid genome for the former and of about 40,000 for E167. There is no homology between the two satellites and neither of them cross-hybridizes to C. elegans or A. Lumbricoides DNA. As deduced from genomic Southern blots, the repeats are arranged in long tandem arrays and the two repeat classes are not intermingled. Northern blot analysis turned out to be negative for both satellites at the pg level using 10 g total Panagrellus redivivus RNA per slot, corresponding to the majority of transcription studies done on satellite DNAs. P. redivivus and C. elegans have nearly identical genome sizes. However, whereas the latter nematode has very little satellite DNA, such sequences represent at least 17% of the P. redivivus genome. This proportion is quite high considering the C-value of merely 70 Mb in P. redivivus, thought to be the lower limit for metazoans. Consequently, maximal genome complexity is of 58 Mb which is approximately equivalent to the genome size of the slime mold Dictyostelium discoideum. Although the P. redivivus genome remains complex enough to englobe the predicted 35,000 kb coding sequences of the closely related nematode C. elegans, the low complexity does set a milestone in terms of the C-value paradox. Moreover, the genome of C. elegans contains 17% of moderately repeated sequences, as found by reassociation kinetics. Some of these sequences are genes which must be equally represented in P. redivivus. Another fraction is made up of transposable elements, an example of which is the PAT element, recently isolated from P. redivivus and present in about 10 to 50 copies per haploid genome. The majority of middle repetitive elements, however, have been poorly studied, but a possible function for these remains the control of gene expression. Such regulatory elements would surely also be required in P. redivivus and if so, would yet decrease the genome complexity to a further extent, perhaps implying the necessity to re-evaluate minimal gene numbers required in simple nematodes.