Abstract
Within the past 100,000 years, Homo sapiens left Africa in search of new opportunities, likely crossing paths with H. erectus in Asia and H. neanderthalensis in Europe. These early pioneers encountered unfamiliar climates, habitats, and food sources (not to mention alien human species). Then, after adjusting to a major climate change following the last ice age, they underwent a dramatic lifestyle switch, from hunting and gathering to agriculture—a change that brought crowded living conditions and new infections. All these radical changes likely precipitated significant genetic adaptations, with selection favoring genotypes most suited to the novel conditions. Indeed, recent studies have found evidence of strong selection on new gene variants reflecting adaptations to disease (conferring resistance to malaria) and dietary changes (lactose tolerance).
Highlights
Because uncontrolled cell division is so dangerous for an organism, the well-behaved cell must know when to divide, and—crucially—when not to
A cell in such a temporary, nondividing state is said to be “quiescent.” Signals that send a cell into quiescence include loss of contact with the underlying surface, too much contact with neighboring cells, and not receiving specific growth factors from the surroundings
The reversibility of quiescence contrasts with the cell cycle arrest induced by inhibition of cyclin-dependent kinase (CDK), a key regulatory protein
Summary
Because uncontrolled cell division is so dangerous for an organism, the well-behaved cell must know when to divide, and—crucially—when not to. After 20 days, there were over 100 genes whose change in expression linked them to quiescence These included those that regulate metabolism and cell division, as might be expected, and genes that suppress the transition to two other cell fates— differentiation and programmed death. The expression of these genes (along with many others) was increased, indicating the active nature of the quiescent state. The identification of different quiescent states, induced by the three different signals, may lead to a better understanding of context-specific control of cell growth during development and repair, in muscle, but perhaps in other tissues as well.
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