Simply define the logic and methods and conclusions from the
experiment the authors described below in quotes. (*Dont copy and
paste from Google) Make sure to define the terms bolded (4
bolded).

“One possible mechanism for the phenotypes in mitotic
tissues of D257A mice is a defect in cellular
proliferation. We derived mouse embryonic fibroblast lines
(MEFs) from D257A and wild-type
littermates and measured the number of
cell doublings before senescence. At 20% oxygen,
both wild-type and D257A MEFs underwent rapid replicative
senescence, whereas neither underwent senescence or reduced growth
after 40 days of culture at 2% oxygen (fig. S9). Thus, accelerated
aging in D257A mice is not likely to be due to an intrinsic defect
in cellular proliferation, or to accelerated cellular
senescence.”