Brain mRNA translatability in rats: changes during long-term dietary restriction in the developmental period of life.

We studied the effects of graded dietary restriction on the amount and translatability of messenger RNA (mRNA) molecule coding for brain proteins during the developmental period of life. Control experiments were performed on newborn, 1-, 3-, 6- and 27-week-old rats, whereas the dietary restriction studies, involving 10, 30 or 50% food deprivation, were conducted on weanling rats for periods of 3 or 24 weeks. Graded dietary restriction for 3 or 24 weeks caused a progressive reduction of the amount and translatability of mRNA in the rat brain. Complementary DNA (cDNA) probe and hybridization studies with [3H]cDNA revealed that food deprivation elicited a shorter species of mRNA or shorter sequences of the same species of mRNA coding for brain proteins and that not all polyadenylates mRNA [poly(A)+ mRNA] sequences found in control rats were present in the dietary-restricted animals. Furthermore, it appeared that food deprivation produced a shorter species of pre-mRNA via decreased polynucleotide elongation. The mRNA content of 27-week-old rat brains increased 12.5 times in comparison to newborns, representing an augmentation that was progressive and related to the developmental period of life of the animals. The translatability of mRNA was enhanced in the brain of 3-week-old rats, as compared to 1-week-old pups, and did not show any change thereafter. From these studies, it can be concluded that graded dietary restriction considerably modified the metabolism of mRNA in the rat brain, whereas minor alterations occurred during the developmental period of life in control animals.