Worm Breeder's Gazette 11(1): 28
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.
Ascaris des (var. suum) and a few other parasitic nematodes undergo chromatin diminution in the somatic precursor cells of the early embryo. In Ascaris, about 25% of the total germ line genome is lost from the somatic cells. Most of the eliminated material is composed of highly repetitive material, but also middle repetitive and single copy sequences are involved. Recently, we have isolated from an Ascaris germ line DNA library a lambda clone containing eliminated single copy DNA. This clone carries at least two different regions which are transcriptionally active during the early embryonic development of Ascaris. By using these DNA sequences as hybridization probes we have isolated two different cDNA clones from a 4 cell stage cDNA library. One of them, EPAL 1, has a length of 540 bp and contains an ORF coding for a 148 amino acid long protein. Sequence comparison with the genomic DNA revealed the existence of at least 3 introns which are flanked by consensus splice sites identical to those found in C. elegans. Northern blot analysis demonstrates that the RNA transcripts of EPAL 1 are specifically present in oocytes as well as in 4 cell embryos. In 4 cell embryos the transcripts are located in the cytoplasm of only two of the four blastomers, as indicated by our preliminary in situ hybridization data. The transcribed region crosshybridizes to three single copy DNA bands within the germ line genome of Parascaris equorum, which are also eliminated from the somatic cells during chromatin diminution. Interestingly, not only the sequence of this gene is conserved between this two parasitic nematodes, but also its behavior during the process of elimination. We therefore suggest, that the process of chromatin elimination serves as an alternative possibility of gene regulation.