Epigenetic Control of Animal Development - Building the Most Complex Structure on Earth - page 175

Unidentified
sensory neurons

Hypothalamus?

ASI sensory
neuroendocrine
cells

Figure 3.43 A neural basis for longevity induced by dietary restriction (DR). DR longevity
is mediated by energy-sensitive central neurons in worms, flies, and possibly mammals. The
ASI neurons mediate DR longevity in worms, and they signal during DR to cause increased
respiration in peripheral tissues and long life spans. Unidentified olfactory neurons mediate
DR longevity in flies. The hypothalamus may mediate DR longevity in mammals.
Source : From Bishop and Guarente (2007) .

protocerebrum increases the life span of male flies by 10.5% and mated females by
33.5% ( Broughton et al., 2005 ). Exposure of Drosophila flies to food-based odorants
reduces their life span and a mutation in one of the olfactory neurons increases aver-
age life span by 60% or 30 days, compared to wild-type flies ( Pletcher, 2012 ).
The role of the insulin/IGF-1 pathway in life spans under the conditions of dietary
restriction seems to be evolutionarily conserved across the metazoan world. From
C. elegans to humans, the activation of DAF-16/FOXO-like transcription factors pro-
motes longer life ( Kenyon, 2010 ). Longevity seems to be regulated by the same basic
mechanisms in vertebrates, where the life-prolonging functions of the amphid neurons
are taken over by the hypothalamus ( Figure 3.43 ). The role of the pathway in mammals
was demonstrated recently in the Ames and Snell dwarf mouse strain, which live about
70% longer than normal mice ( Berryman et al., 2008 ), show reduced signs of aging,
and are resistant to oxidative stress. The link between the pathway and the life span
is mediated by the downstream effects on Forkhead box (FOX) transcription factors
( Dantzer and Swanson, 2012 ).
There is evidence that aging is causally related to degrading changes in the nerv-
ous system. Similarly to humans, microscope electronic studies have shown that
aging in C. elegans is associated with loss of synaptic integrity ( Toth et al., 2012 ).

Metamorphosis: The Same Organism Produces Two Radically
Different Body Plans

It was generally believed that differences in body plans are related to differences
in genes. However, the gene sequencing of many animal species shows that almost