Cytological observations on mitotic and meiotic pairing in males ofDrosophila melanogaster withIn(1)sc 4 sc 8

A cytological study has been carried out on the pairing of the XY chromosomes in somatic cells and in spermatocytes of larvae ofDrosophila melanogaster. Two strains have been studied: one a control strain and the other a carrier of theIn(1)sc ⁴ sc ⁸ inversion on the X chromosome. The data obtained seem to indicate that the absence of the greater region of homology between XY, caused by the presence of theIn(1)sc ⁴ sc ⁸ inversion, results in an approximately equal reduction in the frequencies of mitotic and meiotic pairing of XY. The short arm of the Y chromosome shows marked differences in the pairing with the X chromosome, compared with the control, whereas the long arm shows no variations.     

Complex alterations of the ribosomal gene spacers in mutant sc 8 of Drosophila melanogaster

Extreme changes in the proportions of the rDNA intergenic spacers (IGSs) have previously been demonstrated by us in the X-chromosomal rDNA array of the Drosophila melanogaster mutant sc ⁸ , where nearly all IGSs were found to be reduced in size. We have cloned different structural variants of the Xsc ⁸ ribosomal units and mapped their spacers by restriction endonuclease analysis. Most of the IGSs exhibited complex rearrangements within the subrepeated region at their 5′ terminus. The sequence data revealed the presence of an additional 100 bp subrepeat. In addition, extended deletions/substitutions down to the 18S gene were also found. Examination of the Ysc ⁸ IGS polymorphism indicates that some of the X-chromosomal IGS variants are probably the result of X-Y interchanges. The rarity of alternative recombination products implies that the overabundant deleted spacers in sc ⁸ are generated by nonreciprocal recombination. Our results demonstrate nonrandom distribution of deletional breakpoints within the “1900” region in sc ⁸ and show that the deletions do not truncate the internal IGS subregions at either breakpoint but eliminate them as discrete blocks. Received: 15 April 1997; in revised form: 8 August 1997 / Accepted: 22 August 1997     

Directed alterations of the X-chromosomal ribosomal gene repeats in mutant sc8 of Drosophila melanogaster

The patterns of the ribosomal DNA (rDNA) repeat units in seven Drosophila melanogaster inversional mutants have been studied. Among them, only the In(1)sc⁸ and its deletional derivative Df(1)mal¹² female rDNAs exibited significant reduction in the size of nearly all units, compared to the wild-type females (Canton S, Oregon R). Further investigation shows that each kind of repeat (insertion-free, insertion-containing) in the Xsc⁸ rDNA array is highly enriched with short (reduced to 4 kilobases) intergenic spacers (IGSs). We revealed two main types of rearrangements. Only part of the 4 kb IGSs display variable length deletions (0.2–0.6 kb) at the 5′ ends, within the so-called ‘1900’ base pair (bp) region, recognizable by restriction endonuclease AluI. The presence of additional 100–150 bp DNA in the start portion of this region has also been demonstrated. In contrast, the 3′ end spacer regions, corresponding to the external transcribed spacer, do not show any changes in size. These data indicate how reductions of approximately 1.1 kb DNAs in sc⁸ IGSs, carrying both the rearranged and non-rearranged ‘1900’ sequences, are achieved: the fixed decrease of a number of 240 bp AluI subrepeats, clustered in the central IGS portion, also contribute. None of the other similar inversional mutants examined has so many IGS variants. Therefore, alterations in the Xsc⁸ rRNA gene cluster seem not to be dependent on its inversional status. This revised version was published online in July 2006 with corrections to the Cover Date.     

Puzzling chromosome behavior in triploid females of Drosophila melanogaster

Based on a particular formation of the chromocenter and trivalents in triploid Drosophila females, as well as on asynapsis in pericentromeric regions (which is a result of trivalent competition), an explanation for the increased frequency of crossing over and nonrandom segregation of the X chromosomes and autosomes in the first meiotic division is suggested. It is proposed that a delay in pairing of the pericentromeric heterochromatic chromosome regions combined into a single chromocenter leads to the following: (1) formation of the heteroduplex structures (X structures) takes more time and, consequently, their number and the frequency of crossing over in the paired chromosome regions increases; (2) in nonhomologous chromosomes, the chromocentral connections, which normally degrade in prometaphase, are retained to fulfill a function of coorientation during the first meiotic division.     

Turning males on: activation of male courtship behavior in Drosophila melanogaster

The innate sexual behaviors of Drosophila melanogaster males are an attractive system for elucidating how complex behavior patterns are generated. The potential for male sexual behavior in D. melanogaster is specified by the fruitless (fru) and doublesex (dsx) sex regulatory genes. We used the temperature-sensitive activator dTRPA1 to probe the roles of fru(M)- and dsx-expressing neurons in male courtship behaviors. Almost all steps of courtship, from courtship song to ejaculation, can be induced at very high levels through activation of either all fru(M) or all dsx neurons in solitary males. Detailed characterizations reveal different roles for fru(M) and dsx in male courtship. Surprisingly, the system for mate discrimination still works well when all dsx neurons are activated, but is impaired when all fru(M) neurons are activated. Most strikingly, we provide evidence for a fru(M)-independent courtship pathway that is primarily vision dependent.     

A physical map of the polytenized region (101EF-102F) of chromosome 4 in Drosophila melanogaster

Chromosome 4, the smallest autosome ( approximately 5 Mb in length) in Drosophila melanogaster contains two major regions. The centromeric domain ( approximately 4 Mb) is heterochromatic and consists primarily of short, satellite repeats. The remaining approximately 1.2 Mb, which constitutes the banded region (101E-102F) on salivary gland polytene chromosomes and contains the identified genes, is the region mapped in this study. Chromosome walking was hindered by the abundance of moderately repeated sequences dispersed along the chromosome, so we used many entry points to recover overlapping cosmid and BAC clones. In situ hybridization of probes from the two ends of the map to polytene chromosomes confirmed that the cloned region had spanned the 101E-102F interval. Our BAC clones comprised three contigs; one gap was positioned distally in 102EF and the other was located proximally at 102B. Twenty-three genes, representing about half of our revised estimate of the total number of genes on chromosome 4, were positioned on the BAC contigs. A minimal tiling set of the clones we have mapped will facilitate both the assembly of the DNA sequence of the chromosome and a functional analysis of its genes.     

Cytogenetic analysis of chromosome segments containing radiosensitivity genes in Drosophila. Radiation mutagenesis in the 44-45 region of chromosome 2 of Drosophila melanogaster

The first step of cytogenetic analysis of Drosophila melanogaster chromosome 2 44F-45D containing the radiosensitivity gene rad(2)201 is described. Using various mutation selection systems as well as lines of different origin and two kinds of ionizing radiation--gamma-rays and neutrons--the mutagenesis in the region of interest is characterized at the cytogenetic level. 85 gamma-induced mutations affecting viability were isolated in the 44F 2-4; 45C6-7 interval, 27% of mutations being chromosomal aberrations. 15 radiation-induced aberrations were obtained by selecting mutations at the white gene inserted into the 45D region by P-mediated transformation. The 44F-45D region is characterized by relatively low frequency of deficiency formation and by significant predomination of heterochromatic aberrations in the spectrum of rearrangements. In these regions, the existence of hot spots for heterochromatic aberrations was discovered. As low deletion frequency is not connected with the presence of haplolethal and haplosterile loci in the region studied, the unusual character of radiation mutagenesis reflects possibly the peculiarities in sequence organization of the chromosomal region mentioned or the packaging in the sperm nuclei.     

Mitotic chromosome organization of neuroblastomas induced by the recessive oncogene Lethal(2)giant larvae 4 of Drosophila melanogaster

Mitotic chromosomes in neuroblastomas of Drosophila melanogaster homozygous for the recessive oncogene Lethal(2)giant larvae ⁴ were studied at different larval ages. There was a progressive increase in mitotically active cells with increasing period of tumorous growth. The karyotype of the neuroblastomas generally remained stable. The metaphase chromosomes of the neuroblastomas, however, showed widely varying levels of condensation ranging from highly condensed to highly extended. Staining with the AT-specific fluorescent dye Hoechst 33258 showed extensive resolution of AT-rich heterochromatic blocks in the third and Y chromosomes suggesting their lack of coalescence in the extended metaphases of neuroblastomas. Our results suggest aberrant condensation as a major chromosomal lesion in Drosophila neuroblastomas.     

The meiotic behavior of some single-cistron mutants in the zeste-white region of the Drosophila melanogaster X chromosome

Summary There are two dosage sensitive sites in the zeste-white region of the Drosophila melanogaster X chromosome that affect meiotic chromosome behavior. Single-cistron mutants at essential and female fertility loci in the two segments have been tested for meiotic effects similar to those of deficiencies. None of the mutants have detectable meiotic effects. A de novo search for meiotic mutants in the region has not uncovered any, but the results suggest that a deficiency for the zeste-white region would be useful for detecting meiotic mutants elsewhere in the genome. Tests for interactions between the deficiency and known meiotic mutants support this. Though tentative, these results suggest that non-essential regions need not be devoid of function.Research supported by National Science Foundation grant PCM 79-01824     

Oogenesis in the female sterile (1)42 mutant of Drosophila melanogaster.

The sex-linked mutation fs(1)42 was induced by ethyl methane sulfonate. It has no effect on either the external morphology or longevity of adult hemizygotes or homozygotes. Heterozygotes and hemizygotes are fertile, but homozygotes are sterile. Egg chamber development proceeds through stages 8, and thereafter chambers degenerate. Dying follicle cells are seen in chambers at all positions in the ovarioles. Profollicle cells also die within germaria, and clusters of sister cystocytes take longer than normal to receive their coverings of follicle cells. Egg chambers in the vitellarium contain only about 60% the normal number of follicle cells, these generally have greater lateral dimensions, and their nuclei and nucleoli are also larger than normal. The follicular envelope of mutant chambers often contains gaps through which cystocytes send cytoplasmic projections. Abnormalities seen in development of the fs(1)42 oocyte are likely to be due to its envelope of defective follicle cells.     

Sex Chromosome Meiotic Drive Systems in DROSOPHILA MELANOGASTER I. Abnormal Spermatid Development in Males with a Heterochromatin-Deficient X Chromosome (sc4sc8)

The meiotic drive characteristics of the In(1)sc^4Lsc^8R/Y system have been examined by genetic analysis and by light and electron microscopy. sc⁴sc⁸/Y males show a direct correlation between nondisjunction frequency and meiotic drive. Temperature-shift experiments reveal that the temperature-sensitive period for nondisjunction is at meiosis, whereas that for meiotic drive has both meiotic and post-meiotic components. Cytological analyses in the light and electron microscopes reveal failures in spermiogenesis in the testes of sc⁴sc⁸ males. The extent of abnormal spermatid development increases as nondisjunction becomes more extreme.     

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.