FIG. 7.

By 4 days of age, skeletal-actin-null (−/−) mice show signs of starvation. (A and B) The midthorax cross sections of 4-day old wild-type (+/+) mice (A) exhibit normal amounts of brown fat (arrow), while those of the homozygous null (−/−) mice (B) exhibit a reduced area of brown fat (arrows). (D and E) Microscopic details demonstrate that homozygous null mice (D) had markedly less lipid (small arrows) in brown fat cells than wild-type animals (C) did. Similarly, there is a marked depletion of both liver and muscle glycogen in homozygous null mice (F) relative to wild-type mice (E); i.e., the magenta-colored grains corresponding to glycogen (large arrows) are abundant in panel E and absent in panel F. Note the smaller paraspinal muscle fibers with more frequent central nuclei found in null mice (D) at this age relative to those in wild-type mice (C). Panels C and D are sections that were stained with hematoxalin and eosin; panels E and F are sections that were stained for glycogen with periodic acid-Schiff stain.