[
1992]
In vertebrates, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are polymorphic enzymes presenting both globular and asymmetric forms. In invertebrates, only AChE has been characterized so far that presents a reduced molecular diversity. In insects for example the major molecular form of AChE is an amphiphilic dimeric form attached to the membrane through a glycolipid covalently linked at the C-terminus of each catalytic subunit. This AChE has a substrate specificity intermediate to those of mammalina AChE and BChE. A glycoplipid-anchored 7.5S from has also been observed in the trematode Schistosoma mansoni. Asymmetric forms have never been convincingly reported in invertebrates except in the more evolved animals such as Amphioxius. In the latter case also there is no BChE but AChE presents catalytic properties intermediate to those of vertebrate AChE and BChE. We are now interested in nematode AChE(s) for the following reasons: -several species are agricultural pest and it is important to get further informations on the target of potential nematicides; -it has been shown that at least three different genes code for AChE in Caenorhabditis elegans. It is therefore interesting to see whether the presence of multiple genes results in an increased molecular diversity, to define what are the structural characteristics of each gene product and finally to clone and sequence thee three genes for evolutionary relationships with the other members of the cholinesterase
[
1987]
Work in our laboratory over the past several years has focused on the nature of early determinative decisions in embryos of the free-living nematode Caenorhabditis elegans. Two of these decisions regard determination of sex and determination of the level of X-chromosome expression. C. elegans has two sexes, self-fertilizing hermaphrodites and males. Hermaphrodites normally have two X chromosomes, and males have only one (there is no Y chromosome). Genetic and molecular evidence suggest that C. elegans compensates for this difference in X dosage, not by X inactivation as in mammals, but rather by global regulation of the X chromosome as in Drosophila; that is, X-linked genes are expressed at a higher level per chromosome in 1X than 2X animals, so that levels of X expression are similar in the two sexes. Also as in Drosophila, the primary signal that dictates both sex determination and level of X expression in C. elegans is the ration of the number of X chromosomes to the number of sets of autosomes (X/A ratio) rather than the absolute number of X chromosomes.|