Disruption of the gene encoding the mitogen-regulated translational modulator PHAS-I in mice.

PHAS-I is the prototype of a group of eIF4E-binding proteins that can regulate mRNA translation in response to hormones and growth factors. To investigate the importance of PHAS-I in the physiology of the intact animal, we disrupted the PHAS-I gene in mice. Tissues and cells derived from the knockout mice contained no detectable PHAS-I protein. A related protein, PHAS-II, and eIF4E were readily detectable in tissues from these animals, but neither appeared to be changed in a compensatory manner. Mice lacking PHAS-I appeared normal at birth. However, male knockout mice weighed approximately 10% less than controls at all ages, whereas female weights were similar to those of controls. Both males and females were fertile. Tissues from adult animals appeared to be normal by routine histological staining techniques, as were routine blood cell counts and chemistries. Fibroblasts derived from PHAS-I-deficient mouse embryos exhibited normal rates of growth and overall protein synthesis, responded normally to serum stimulation of ornithine decarboxylase activity and cell growth, and rapamycin inhibition of cell growth. Under these experimental conditions, PHAS-I is apparently not required for the normal development and reproductive behavior of female mice, but is required for normal body weight in male mice; the mechanisms responsible for this phenotype remain to be determined.