Replicating DNA molecules from eggs ofDrosophila melanogaster

Eggs ofDrosophila melanogaster were lysed with sodium dodecyl sulphate within 110 minutes after laying and the lysate prepared for electron microscopy by the protein monolayer technique. Long, non-circular DNA molecules were found with a form suggesting they contained either a single replicated region, or two, three or four replicated regions arranged in tandem. Each replicated region was delimited by two forks. The two segments of DNA spanning the region between the forks were approximately equal in length and appeared to be totally or almost totally double-stranded. The appearance of replicating molecules was not altered by digestion with pronase or treatment with phenol or chloroform. The lengths of replicated regions varied from 0.2 to 22.1 with a mean value of 2.97 . The distances between midpoints of adjacent tandemly arranged replicated regions ranged from 1.2 to 9.7 with a mean value of 3.87 . Circular molecules found in these preparations, and presumed to be of mitochondrial origin, were estimated from comparative length measurements with circular double-stranded DNA molecules from the bacteriophages lambda, X174 and fd to have a molecular weight of 12.36 X 10⁶ daltons.     

Alpha and beta heterochromatin in polytene chromosome 2 ofDrosophila melanogaster

The formation of alpha and beta heterochromatin in chromosomes of Drosophila melanogaster was studied in salivary glands (SGs) and pseudonurse cells (PNCs). In SGs of X0, XY, XYY, XX and XXY individuals the amounts of alpha heterochromatin were similar, suggesting that the Y chromosome does not substantially contribute to alpha heterochromatin formation. Pericentric heterochromatin developed a linear sequence of blocks in PNCs, showing morphology of both alpha and beta heterochromatin. In situ hybridization with Rsp sequences (H _o clone) revealed that the most proximal heterochromatic segment of the mitotic map (region h39) formed a polytenized block in PNCs. Dot analysis showed that the clone had a hybridization rate with PNC-DNA very close to that with DNA from mainly diploid head cells, whereas the homologous SG-DNA was dramatically underrepresented. A similar increase of DNA representation in PNC was found for AAGAC satellite DNA. The mitotic region h44 was found not to polytenize in the SG chromosome, whereas in PNC chromosome 2 this region was partly polytenized and presented as an array of several blocks of alpha and beta heterochromatin. The mapping of deficiencies with proximal breakpoints in the most distal heterochromatin segments h35 in arm 2L and h46 in 2R showed that the mitotic eu-heterochromatin transitions were located in SG chromosomes distally to the polytene 40E and 41C regions, respectively. Thus, the transition zones between mitotic hetero- and euchromatin are located in banded polytene euchromatin. A scheme for dynamic organization of pericentric heterochromatin in nuclei with polytene chromosomes is proposed. Received: 17 November 1995; in revised form: 10 April 1996 / Accepted: 18 September 1996     

Genetic analysis of a Minute mutation in the distal region of the second chromosome ofDrosophila melanogaster

Genetic organization of a proximal region of the second chromosome inDrosophila melanogaster has been analysed by saturation mutagenesis. Seven alleles were uncovered in this region in addition to the one previously known. Besides this, quite a few mutations were isolated that non-complemented more than one group of lethals and looked very much like deletions of varying extent. Except one, all the lethals complemented M(2)z.     

Enhancer of bithorax: a mutation ofDrosophila melanogaster

A recessive lethal mutation ofDrosophila melanogaster which as heterozygote enhances the phenotype of several mutant combinations of thebithorax-complex (BX-C) is described here; it is calledEnhancer of bithorax (E(bx)²). The linkage group and the map position of this mutation have been determined; it maps on the third chromosome at - 1.65 map units. It has been cytologically localised to the region 61A1-6. This locus is a possible candidate for positive control of BX-C.     

Genes and loops in 320,000 base-pairs of the Drosophila melanogaster chromosome

We have mapped the DNA sequences bound to the nuclear scaffold along 320,000 base-pairs of a genetically well-defined region of the Drosophila chromosome. We have found that the domains delimited by the scaffold attachment regions are heterogeneous in size (ranging from 26,000 to 112,000 base-pairs in this interval), and that the attachment sites are within unique sequences as judged by blot hybridization. We also found that looped domains contain up to five, or even eight, unrelated genes including, in some cases, more than one transcribed gene. The loop organization unravelled here in cultured cells does not correspond to the banding pattern seen in salivary gland polytene chromosomes.     

Gust J, a salt-insensitive mutant ofDrosophila melanogaster

A set of 340 P insert lines on the X chromosome and the autosomes were screened for altered responses of the labellar chemoreceptors to salts and sucrose. A mutant linegustJ was isolated in which the electrophysiological response of the salt-sensitive neuron to Na⁺ in the sensilla of the proboscis is reduced. The responses to KC1 and sucrose are unaffected. In feeding tests,gustJ flies have Na⁺-specific defects. Heterozygotes ofgustJ with two other salt mutantsgustE andBE1323 are normal. Multiple alleles ofgustJ have been obtained by excision of the original P element. All mutants have defects in Na⁺ sensing specifically, thus defining a new gene that affects Na⁺ response of the fly.     

Complete replication of DNA in polytene nuclei of salivary glands ofDrosophila melanogaster

Summary Combined cytophotometric and autoradiographic experiments are performed on individual polytene salivary gland nuclei of X/X-female and X/Y-male larvae ofDrosophila melanogaster, DNA measurements of unlabeled nuclei reveal complete douplings of all 4C DNA quantity during polytenization. These new data do not agree with the hypothesis of heterochromatic underreplication.     

Operations on the pupal wing ofDrosophila melanogaster

Journal of Genetics -     

Interaction between a picornavirus and a wild population ofDrosophila melanogaster

Summary Drosophila C virus (DCV) has a considerable impact on ovarian morphogenesis inDrosophila melanogaster host populations. This virus also affects the developmental time and the fresh weight of infected females. In order to investigate the hypothesis that DCV may play a role in the dynamics ofDrosophila populations, the fertility and embryonic and larvo-pupal death rates of a host population and that of five DCV-free populations were determined. A comparison of two populations, one of them DCV-free, the other infected, suggested that the fertility of the DCV-infected flies was higher than that of uninfected flies, despite a greater larvo-pupal death rate. Fertility of the infected flies was greater among the infected population than for the DCV-free populations. The DCV-free populations originated from five different localities. The virus clearly does have an impact on the biotic potential of its host population. This paper reports for the first time a positive interaction between a viral population and a host population as it increases certain parameters of host population dynamics.