You can learn a lot by looking at a genome, the full set of genes
in an organism. You can learn even more by looking at several at
once — a field called comparative genomics. Among the more
interesting work coming out in July were two NIH-funded comparative
genomics studies, both published in Science a week apart.
One compared 8 mammalian genomes; the other, those of 3 deadly
The mammalian study, funded in part by NHGRI and NCI, aimed to
explore mammalian chromosome evolution by aligning and comparing
the human, mouse, rat, cow, pig, dog, cat and horse genomes. In
an impressive feat, the researchers reconstructed the genomes of
long-extinct mammals and determined the rates of mammalian chromosome
evolution. They found that rates dramatically accelerated around
65 million years ago, a period of mass extinction (most notably,
of the dinosaurs) that marked the end of the age of reptiles and
the arrival of the age of mammals. These results might be expected,
given the rapid expansion of mammals into new ecological niches.
A more surprising finding was that chromosome rearrangements tended
to occur in the same regions. Researchers had long thought that
mammalian chromosomes evolved through random breaks, but this study
found that nearly 20 percent of breakpoint regions were reused.
These "hotspots" tend to have a high gene density. They also seem
to be associated with the more frequent cancer-associated chromosome
abnormalities. Rearrangements near these breakage hotspots might
activate genes that trigger cancer or inactivate genes suppressing
it. As more genomes become available, these relationships will
The other research came in the form of a set of studies, partly
supported by NIAID, that decoded the genomes of 3 trypanosomatids.
These parasites, which cause leishmaniasis, Chagas' disease and "sleeping
sickness," collectively cause disease and death in millions of
people, primarily in developing countries. There are no vaccines
for these diseases and no ideal drugs for dealing with them.
Although the 3 parasites share many general characteristics, each
is transmitted by a different insect, targets different tissues,
has distinct disease pathogenesis and uses different immune-evasion
strategies. Nevertheless, comparative genome analysis revealed
a core of about 6,200 common genes. A drug designed to target such
conserved core processes could potentially be useful against all
trypanosomatids. These studies also revealed a plethora of unique
potential drug targets. This research will hopefully now spur the
development of better diagnostics and therapeutics for these deadly