Puff induction in larval salivary gland chromosomes ofDrosophila hydei sturtevant

The puffing pattern in salivary chromosomes of third instar larvae ofDrosophila hydei was studied following treatment with various gases, potassium cyanide, or vacuum. It was found that a number of specific puffs appear when anaerobiosis is followed by exposure to air or oxygen. These puffs seem to be independent of larval age, and are identical with some of those puffs which can be induced by raised temperature. It is suggested that the chromosomal loci involved, are connected with respiration.     

Experimental puffs in salivary gland chromosomes of Drosophila hydei

Summary In Drosophila hydei abnormal puffing activities could be induced by temperature shocks and treatments with 1.2% and 1.4% KCl solutions. After temperature shocks in vivo and in vitro, a number of puffs showed a similar change in activity.Other puffs were found to show a change in activity only after a distinct treatment.Some of the puffs, specific for temperature shocks, showed a change in activity only at a distinct stage of development.In discussing the results, particular attention is paid to puffs observed in common after all treatments.Dedicated to Prof. H. Bauer on the occasion of his sixtieth birthday.     

The banding pattern of the salivary gland chromosomes of Drosophila hydei

The banding pattern of the salivary gland chromosomes of D. hydei was investigated in the electron microscope. We compared the banding pattern of squashed chromosomes with non-squashed preparations and observed that the fixation and squash procedure we used does not introduce artificial changes in the banding pattern of the chromosome. An electron microscopic map was made of the banding pattern of the distal half of the second salivary gland chromosome. On the basis of the number of bands in this part of the second chromosome we calculated a total of about 3700 bands for the whole set of polytene chromosomes of D. hydei. Our data indicate a similar number of bands in the salivary gland chromosomes of evolutionary remote Drosophila species like D. hydei and D. melanogaster.     

Nondisjunction of the X chromosomes in females ofDrosophila hydei

An investigation of nondisjunction inDrosophila hydei has disclosed that spontaneous primary nondisjunction of the X chromosomes occurs with a frequency of 1/13000, and secondary nondisjunction with a frequency of 1/3500. These rates are much lower than the ones previously reported forDrosophila melanogaster which are about 1/1000 for primary nondisjunction and 1/50 for secondary nondisjunction.The low rate of secondary nondisjunction inhydei is attributed to the much greater genetic length of the X chromosome and the corresponding reduction in noncrossover X's available for distributive pairing with the Y chromosome.The low rate of primary nondisjunction is attributed to both a reduction in noncrossover X chromosomes, and to the large heterochromatic arm of the X chromosome which, it is suggested, makes the X centromere a strong centromere. Thus, it is further suggested, the reduction in noncrossover chromosomes reduces the opportunity for nonhomologous distributive pairing and nondisjunction of the type involving noncrossover chromosomes. Nondisjunction of the type involving crossover chromosomes then is prevented by the success of the strong centromeres in overcoming entanglements that would lead to nondisjunction in the case of ordinary or weak centromeres.This investigation was supported in part by U.S. Public Health research grant GM 12093 and in part by a National Science Foundation research grant 14200.     

The replicative organization of DNA in polytene chromosomes ofDrosophila hydei

Salivary-gland nuclei ofDrosophila hydei were pulse-labeledin vitro with³H-thymidine and studied autoradiographically in squash preparations. The distribution of radioactive label over the length of the polytene chromosomes was discontinuous in most of the labeled nuclei; in some nuclei the pattern of incorporation was continuous. Comparison of the various labeling patterns of homologous chromosome regions in different nuclei showed that specific replicating units are replicated in a specific order. By combining autoradiography with cytophotometry of Feulgen-stained chromosomes, it was possible to correlate thymidine labeling of specific bands with their DNA content. The resulting data indicate that during the S-period many or perhaps all of the replicating units in a salivary-gland nucleus start DNA synthesis simultaneously but complete it at different times. Furthermore, the data support the hypothesis that the chromomere is a unit of replication or replicon. The DNA content of haploid chromomeres was found to be about 5×10^-4 pg for the largest bands inDrosophila hydei. From the results of H³-thymidine autoradiography and Feulgen-cytophotometry on neuroblast and anlage nuclei it was concluded that during growth of the polytenic nucleus heterochromatin is for the most part excluded from duplication. The results of DNA measurements in interbands of polytene chromosomes do not agree with a multistrand structure for the haploid chromatid. A chromosome model is proposed which is in accordance with the reported results and with current views concerning the replicative organization of chromosomes.     

A comparison of banding patterns in salivary gland chromosomes of two species ofDrosophila

An attempt was made to compare the details of chromosome structure between two distantly related species ofDrosophila, D. melanogaster andD. hydei, which belong to different subgenera. Several short stretches of salivary gland chromosomes were selected on the basis of presumed homologous markers, either mutants associated with chromosome breaks, or experimental puffs. Banding patterns were compared in map diagrams, compiled from photographs. It proved possible to correlate with fair accuracy at least a short sequence of bands in each of the examples studied. The map regions were however very different otherwise. It was not possible to judge in how far this is a consequence of major or very small rearrangements, or other types of change. The chromosomal location of one permanent puff and of several others some of which are formed normally during pupation, and some of which appear after a period of oxygen deprivation, was found to be in complete agreement with genetical data which indicate homology of chromosomes 2 (hydei) with3R (melanogaster), and of 4 with3L. On the other hand, relative position and sequence of these puffs within the chromosome are different in the two species. Supported by the Netherlands Organization for the Advancement of Pure Research, Grant 913-28.     

Established cell lines ofDrosophila hydei

Summary Four cell lines have been isolated fromDrosophila hydei embryos. Three lines have a normal XY karyotype, the fourth has an XO karyotype with an additional small heterochromatic fragment. The cells contain presumable cytoplasmic virus like particles. This work was supported by a travel grant to Dr. N. H. Lubsen from the Netherlands Organization for the Advancement of Pure Research (Z. W. O.).     

The fate ofDrosophila hydei anlagen in heteroplastic transplantations

Summary Imaginal discs and larval brains of wildtype andlethal (3) giant larvae ofDrosophila hydei were transplanted into adult foreign hosts and examined after about 2 weeks. The transplants behaved very differently in different host species, viz. 6 species ofDrosophila, 5 other species of Diptera, and 3 species belonging to the Coleoptera or Dictyoptera, whereby the degree of incompatibility was more or less correlated with taxonomic distances. One notable exception was found in the cheese skipper,Piophila casei, an entirely compatible host.     

The salivary gland chromosomes of Anopheles hectoris

The salivary gland chromosome map of Anopheles hectoris is described and figured. It is proposed that this map be considered the standard for this species. The hectoris chromosomes show a close relationship to those of Anopheles pseudopunctipennis pseudopunctipennis.     

Nucleolus-organizing regions in salivary gland chromosomes of Drosophila melanogaster

Summary The nucleolus of the salivary gland nucleus of Drosophila melanogaster is formed by nucleolus-organizing regions which exist in the heterochromatin of the sex chromosomes. This interpretation is supported by the discovery of a series of induced chromosomal alterations involving transfer of nucleolus-forming regions to euchromatic sections of the chromosomes.     

Puffing in salivary gland chromosomes of picture-winged Hawaiian Drosophila

A portion of the X chromosome was examined for puffing activity shortly before puparium formation in several species of Hawaiian Drosophila. A large puff was induced by incubating excised salivary glands with ecdysone. In two of the seven species studied, the region in question has been moved by inversion to a new position relative to the banding sequence in the other species, but the reaction to ecdysone remained unchanged. Another puff, not affected by short term incubations with ecdysone, displayed different degrees of activity in some homosequential species, affording a cytological means for distinguishing these species.