Abstract
Students of human evolution got a big boost when the draft sequence of the chimp genome was published in 2005. Now their challenge is to comb through the combined 6 billion nucleotides for clues to the evolutionary forces that made humans odd man out in the primate family tree. Chimp and human DNA nucleotides differ by just 1.23%, sufficient genetic variation for natural selection to create a bipedal, big-brained primate lineage but small enough to suggest that every mutation has an evolutionary tale to tell.
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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