Cytoplasmic incompatibility

Wolbachia endosymbionts are abundant in arthropods, where they promote a variety of reproductive manipulations, including feminization of genetic males, parthenogenesis and cytoplasmic incompatibility. Wolbachia is also present in filarial nematodes and has recently attracted a great deal of attention. This chapter reviews the studies so far published and discusses potential implications and future research prospects. Since this is a relatively young field, the chapter will also refer to unpublished studies and will include some speculation. The aim is to stimulate further work on the subject. 

Fine, P.E.M. (1978) On the dynamics of symbiote-dependent cytoplasmic incompatibility in culicine mosquitoes. Journal of Invertebrate Pathology 30, 10-18. 

Hurst, L.D. and McVean, G.T. (1996) Clade selection, reversible evolution and the persistence of selfish elements the evolutionary dynamics of cytoplasmic incompatibility. Proceedings of the Royal Society of London B 263, 97-104. 

O Neill, S.L., Giordano, R., Colbert, A.M.E., Karr, T.L. and Robertson, H.M. (1992) 16S rRNA phylogenetic analysis of the bacterial endosymbionts associated with cytoplasmic incompatibility in insects. Proceedings of the National Academy of Sciences USA 89, 2699—2702. 

In the case of the ER, when a region of 20 amino acids between 250 and 270 is missing, the receptor is located strictly in the cytoplasm. Domains of similar size and function have also been located in the receptors of glucocorticoids and of progesterone. The zone of nuclear location overlaps with one of the sequences for interacting with hsp90, which at the same time is next to the DBD. The coincidence of the three functions in a space so restricted implies that they are totally or partly incompatible sterically (Evans 1989 Gruber et al. 2002). 

Stem cells are required wherever there is a recurring need to replace differentiated cells that cannot themselves divide. There may be several reasons why a cell is terminally differentiated. The cell nucleus is digested, as in the outermost layers of the skin, or is extruded, as in the mammalian red blood cells. Alternatively, the cytoplasm may be heavily encumbered with structures, as in myofibrils of the striated muscle cells, which would hinder cell duplication. In other terminally differentiated cells the chemistry of differentiation may be incompatible with cell division. In any case, renewal must depend on stem cells. 

The arrector piK muscle is under adrenergic control and does not respond to a local increase in ACh concentration. The fibroblasts and myofibroblasts are very interesting cells as far as the possibilities of the action of DMAE is concerned. Eibroblasts have cytoplasmic myofilaments that help them move in the dermis when necessary. There are different types of fibroblast subpopulations. Some authors maintain that these different subpopulations expand when they are needed through different phenotype expressions, whereas others believe that these subpopulations coexist permanently in the dermis. These two hypotheses are not incompatible. Myofibroblasts (MEBs) are phenotypicaUy modified fibroblasts that have the secretory capacity of fibroblasts, which helps them synthesize strong fibronectin fibers. They express the phenotypic characteristics of nonmuscle cells, but with the contractile capacities (of SMCs) that make them responsible for most of the phenomena of fibrotic contraction in the body. The fibronectin fibers syn-... 

Most of the triazine tolerant weed biotypes Identified to date have economic relatives but few if any are as closely related to economic crops as the birds rape. To date, this cytoplasm has been transfered to oilseed rape, rutabaga and oriental mustard by several breeding groups. Partial cross-compatibi 1 ity with several other Brassica species including the cole crops, and other more distantly related species (eg, Diplotaxis and Raphanus species) may permit transfer by classical methods (perhaps assisted by embryo rescue techniques). Chloroplast or mitochondrial X nuclear Incompatibilities however, may limit this potential. As other triazine tolerant weed biotypes emerge, opportunities for transfer to closely related economic species by classical methods may evolve. 

Hybrid varieties could be developed more quickly without canola quality. This approach appears to have been taken in China. In that country, hybrid cultivars, some using incompatibility and others utilizing cytoplasmic male sterility, are under development and appear to be close to commercial utilization (Stefansson, 1980). 

S. cerevisiae is the only eukaryotic organism used for expression of the n-butanol pathway. The possible incompatibility of bacterial genes in a eukaryotic organism is likely one of the hmitations. Probably the biggest obstacle concerns the poor availability of acetyl-CoA in the cytoplasm (Pronk et al. 1996), which is where the expressed butanol pathway enzymes are active. 

Intraspecific crossing with both non-cultivated strains e.g. weedy races) and among non-transformed cultivars is appropriately covered here (perhaps with a table or diagram), including any genetic or cytoplasmic constraints or limitations to crossing e.g. cytoplasmic or nuclear sterility, incompatibility systems). Interspecific crosses are addressed in the following section. 

---