IN VITRODEVELOPMENT OF INSECT TISSUES. I. A MACROMOLECULAR FACTOR PREREQUISITE FOR SILKWORM SPERMATOGENESIS

Abstract

1. Naked germinal cysts removed from the testes of diapausing Cynthia or Cecropia pupae and cultured in vitro undergo meiosis and spermatogenesis only when the culture medium contains a macromolecular (MF) which is present in insect blood. The factor in question is undialyzable, heat-sensitive, and interchangeable among the three genera of saturniid silkworms which were studied. Its partial purification was achieved by ammonium sulfate fractionation and by precipitation at low ionic strengths.2. In appropriate experiments, ecdysone was found to have no obvious effect on cultures of naked cysts and was neither able to replace nor enhance the activity of MF in the in vitro assay.3. MF is present in the blood plasma of both male and female pupae; its titer undergoes large and systematic changes when diapausing Cynthia pupae are stored at 25° C for up to six months.4. In plasma collected from uninjured pupae, MF was routinely present except during a brief period 8 to 10 weeks after pupation. Howeve...