Organization of Polysomes from Pre-existing Ribosomes in Chick Oviduct by a Secondary Administration of Either Estradiol or Progesterone

Abstract Estradiol stimulates the differentiation of tubular glands in the magnum portion of the chick oviduct. These glands synthesize egg white proteins, predominantly ovalbumin. When chicks are given estradiol daily for 10 days (primary stimulation) and are then withdrawn from hormonal treatment, there is a decrease in oviduct size, a decrease in protein concentration, and a reduction in protein and RNA synthesis. If estradiol or progesterone are administered again (secondary stimulation), protein and RNA synthesis are re-established within 12 to 24 hours. During this time, the rate of ovalbumin synthesis increases several hundred fold, without dependence on cell proliferation. Although the biochemical responses observed during secondary stimulation are similar with both estradiol and progesterone during the first 18 hours, at later times the rate of protein synthesis continues to rise with estradiol but not with progesterone. Biochemical and ultrastructural studies indicate that the increased rate of protein synthesis during secondary stimulation is associated with an organization of ribosomes into polysomes within gland cells. During the early stages of secondary stimulation the polysomes are assembled predominantly from pre-existing single ribosomes. Later, newly synthesized ribosomes enter the polysomes. Both new and old ribosomes seem to be in the same pool.