Metabolic DNA in Tipula oleracea

Summary

In Tipula oleracea females 2n=6+XX (Diptera) a Feulgen positive body is present in the oogonia and oocyte nuclei. This body appears in the nucleus at the oogonial divisions that precede meiosis. It gets larger by leptotene, attaining a diameter of 6 microns, and at diplotene suddenly disintegrates. By metaphase I the body is not seen.

Injection of tritiated thymidine into the larvae leads to a heavy labelling of the Feulgen positive body. The body is found to synthesize DNA at a different period of time from the chromosomes, and there is an intermediate period when the synthesis of the two nuclear structures overlaps.

The tritium labelled thymidine is released from the body between the third and fourth day of pupal life. At this time the yolk granules in the cytoplasm become particularly conspicuous.

When the body disintegrates the labelled material becomes easily diluted. The volume of the nucleus and of the cytoplasm are sufficiently large to dilute this material in such a way that it easily becomes indistinguishable from background radiation.

Spectrophotometric measurements of the body reveal that it contains four times more DNA per unit area than the chromosomes. The area of the body is 28.3 square microns and that of the chromosomes 78.5 square microns. This means that the amount of DNA in the body is of a higher order of magnitude than that found in all the chromosomes.

This large amount of DNA becomes suddenly available either to the chromosomes or other cellular components. DNA can carry its own genetic information to other cellular components.