The molecular structure of the DNA fragments eliminated during chromatin diminution in Cyclops kolensis.

Presumptive somatic cells of the copepod Cyclops kolensis specifically eliminate a large fraction of their genome by the process of chromatin diminution. The eliminated DNA (eDNA) remains only in the germline cells. Very little is known about the nature of the sequences eliminated from somatic cells. We cloned a fraction of the eDNA and sequenced 90 clones that total 32 kb. The following organizational patterns were demonstrated for the eDNA sequences. All do not contain open reading frames. Each fragment contains 1-3 families of short repeats (10-30 bp) highly homologous within families (87%-100%). Most repeats are separated by spacers up to 50 bp long. Homologous regions were found between fragments, motifs from 15-300 bp in length. Among fragments there occur groups in which the same motifs are ordered in the same fashion. However, spacers between the motifs differ in length and nucleotide composition. Ubiquitous motifs (those occurring in all fragments) were identified. Analysis of motifs revealed submotifs, each occurring within several motifs. Thus, motifs may be regarded as mosaic structures composed of submotifs (short repeats). Taken together, the results provide evidence of a high organizational ordering of the DNA sequences restricted to the germline. With this in mind, it appears incorrect to refer to this part of the genome as junk. Moreover, eDNA is redundant for only the somatic cells-its function is to be sought in germline cells.

Molecular characterization of the singed wings locus of Drosophila melanogaster.

BACKGROUND: Hormones frequently guide animal development via the induction of cascades of gene activities, whose products further amplify an initial hormonal stimulus. In Drosophila the transformation of the larva into the pupa and the subsequent metamorphosis to the adult stage is triggered by changes in the titer of the steroid hormone 20-hydroxyecdysone. singed wings (swi) is the only gene known in Drosophila melanogaster for which mutations specifically interrupt the transmission of the regulatory signal from early to late ecdysone inducible genes. RESULTS: We have characterized singed wings locus, showing it to correspond to EG:171E4.2 (CG3095). swi encodes a predicted 68.5-kDa protein that contains N-terminal histidine-rich and threonine-rich domains, a cysteine-rich C-terminal region and two leucine-rich repeats. The SWI protein has a close homolog in D. melanogaster, defining a new family of SWI-like proteins, and is conserved in D. pseudoobscura. A lethal mutation, swit476, shows a severe disruption of the ecdysone pathway and is a C>Y substitution in one of the two conserved CysXCys motifs that are common to SWI and the Drosophila Toll-4 protein. CONCLUSIONS: It is not entirely clear from the present molecular analysis how the SWI protein may function in the ecdysone induced cascade. Currently all predictions agree in that SWI is very unlikely to be a nuclear protein. Thus it probably exercises its control of "late" ecdysone genes indirectly. Apparently the genetic regulation of ecdysone signaling is much more complex then was previously anticipated.