Worm Breeder's Gazette 12(3): 76 (June 15, 1992)

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.

Transcriptional Activity in Ascaris Embryos Begins Just After Fertilization

A. Spicher, A. Etter, H. Tobler, F. Muller

Institute of Zoology, University of Fribourg, CH-1700 Fribourg, Switzerland

During animal embryogenesis, the genome becomes transcriptionally active and contributes increasingly to the control of development. C. elegans embryos were shown to start transcriptional activity prior to the approximately 30-cell stage at which gastrulation begins (Schauer and Wood, Dev. 110 (1990), 13031317). In Ascaris, by performing in vitro nun-off transcription assays with nuclei from synchronous populations of early embryonic stages, transcriptional activity was found as early as the 4-8-cell stage (Cleavinger et al., Dev. Biol. 133 (1989), 600-604). These findings suggest that both, Ascaris and C. elegans embryos, are transcriptionally active very early in development.

Recently, we have identified and isolated an Ascaris gene (Fert-1), which is expressed even earlier in development, namely just after fertilization. Fert-1 is a single copy gene that is expelled during the process of chromatin diminution from all somatic precursor cells. It yields a 560 nt long, polyA+ transcript of unknown function, which is composed of two exons and carries a spliced leader at its 5'end. A short ORF encodes a putative polypeptide.

No Fert-1 RNA is detected in spermatids, oocytes and in mature germ cells prior to fertilization, which are located in the oviduct near the junction to the uterus. Transcripts are first found in fertilized eggs and are then persisting in increasing amounts throughout the early embryonic development until the stage where chromatin diminution occurs. After the elimination of the gene, its poly A+ transcription products disappear and are no longer detectable after the sixth day of embryonic development.

Fert-1 provides a striking example of Ascaris early embryonic gene activity: Transcription of this non-maternal RNA species starts immediately after fertilization. Our data thus show that gene expression in Ascaris is switched on even in the earliest stages of embryonic development. Restriction of Fert-1 gene activity to early embryonic stages suggests a possible developmental function during initial embryonic differentiation. It should be interesting to see whether a homologous gene can be found in C. elegans and what its biological function might be.

Literature Cited:

Schauer and Wood, Dev. 110 (1990), 13031317

Cleavinger et al., Dev. Biol. 133 (1989), 600-604