"Can genes explain biological complexity?" The answer is perhaps. It depends in part on where you start
counting genes. If we define the heritable entity to include the entire
gene matrix, then the answer is maybe. If we attempt to define the
heritable matrix by the "individual" genes, the answer is probably no. As
has been recently noted in the daunting series of articles on Wolbachia,
the expression of an organism must include contributions not only from the
heritable genetic contributions of the parent organism but also other
heritable components arising from invasive elements and possibly an array
of proteins that help direct the differentiation processes to a viable
organism.
As noted in the news article "DNA sequences provide grist for microbiologists" (Science, 19 Feb. 1999, p. 1105) by Elizabeth Pennisi, the bacterium is best known for infecting insects, where they are
transmitted from generation to generation through the germ cells.
Depending on the species, it can make the host infertile or alter the sex
ratio of the offspring, such that only one sex survives. In contrast, in
filaria the Wolbachia seem key to fertility, thereby making the worms
susceptible to antibiotics that attack the bacteria. The bacteria "seem to
have a pretty interesting role in terms of therapy," Slatko reported. So
he and his colleagues have decided to sequence a Wolbachia genome, hoping
it will lead to new ways to control filarial infections.
...But as consortium members began analyzing the worm's genetic
material, "we kept finding bacterial sequences."
Wolbachia live in the cytoplasm of insect cells and apparently do
no harm. These endosymbionts do, however, have a startling effect on the
reproduction of their insect hosts, which has led biologists to speculate
that Wolbachia might contribute to reproductive isolation and the creation
of new insect species (speciation). Bordenstein et al. (1) now provide
evidence that this indeed may be the case.
This arrangement ensures that Wolbachia (which are passed to
offspring only through females) spread rapidly through the host species
because uninfected females that mate with infected males cannot produce
offspring.
Starting 25 years ago, a few researchers had noticed "dense
bodies"--possibly bacteria--in the embryonic and adult tissues of several
species. One report even suggested that antibiotics seem to have antiworm
effects. But until recently, "that work was not followed up on," says
Guiliano.
"If you kill the Wolbachia, you will [eventually] kill the [infected]
nematodes" by preventing their reproduction, explains Scott O'Neill, a
vector biologist at Yale University in New Haven, Connecticut.
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