LAIRVAL DElVELOPMIENT IN SCIARA COPROPHILA WITHOUT THE FORMA TION OF

  • CHROMOSOMIAL PUFFS, JOALENE GOIDLt

Abstract

C(onspicuous changes, the appearance of puffs, occur in the chromosomes of certain cell types during the period of larval development preceding pupation in the Diptera. Autoradiographs indicate that the puffs are sites of intense RNA synthesis. The experiments reported iI this paper show that in Sciara coprophila essentially normal development can occur without the appearance of puffs aIld without the intense synthesis of RNA at the chromosomal sites at which puffs ordinarily appear, although RNA synthesis proceeds normally elsewhere in the chromosomes. Larval development without puffs was produced by feeding the larvae cortisone, a vertebrate hormone Iiot normally present in insects. The patterll of bands and interbands in giant polyteine chromosomes of Diptera is generally regarded as reflecting the genetic organization of the constituent chromosomal strands. During Dipteran larval development, striking morphological and chemical changes occur in the giant chromosomes. Some of the morphological changes are gross and involve pronounced loosening of the chromosomal structure. 1 These have been referred to as puffs, a term which was coined by Bridges2 to describe this structural modification of the X chromosome in Drosophila. Since then the term has been used rather looselv to describe a number of morphologically different structures. In SCiara, l)oulson and -Metz3 have described at least ten regions which become expanded to form puffs, some areas involving as many as 30 bainds. Beermann,4 however, found that puffing is restricted to single bands, pairs of bands, or bands in conjunction with adjacent interbands. Puffs have been considered by Beermann5' 6 and Pavan7 to be the "loci of active genes." When gene action was found to be mediated through the synthesis of ribonucleic acid and when it was found in autoradiographic studies that intense RNA synthesis occurs in the puffs,8' the association of puffs with gene activity was confirmed. Further evidence for the association of puffs with geine activity was the recent demonstration that actinomycill D, which specifically inhibits DNA-dependeint RNA synthesis, reduced the size of the puffs coisiderably.'0 Puffed chromosomal regions have been referred to as "activated" geines, aid those which are Iot puffed are "more or less silent oInes."11 In two receent reviews, Clever10' 12 has stated that it "may now be taken for granted that puffs represent active gene loci" and that the giant chromosomes of Diptera offer "a very suitable object for studies on gene activity because it is possible to distinguish morphologically active chromosomal loci from inactive ones." Puffs in Sciara were distinguished from the far smaller swellings in the chromosomes by Poulson and Metz,3 and the latter were termed bulbs. In a recent paper Gabrusewycz-Garcial3 noted that bulbs, unlike puffs, are not restricted to particular stages of development. In Chironottiusj Beermann has emphasized that ony]v the large puffs are associated with the developmental events specific for each cell type. Despite this distinction

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Cite this paper

@inproceedings{PUFFSLAIRVALDI, title={LAIRVAL DElVELOPMIENT IN SCIARA COPROPHILA WITHOUT THE FORMA TION OF}, author={CHROMOSOMIAL PUFFS and JOALENE GOIDLt} }