Super-unstable mutations associated with P-M hybrid dysgenesis in Drosophila melanogaster

Super-unstable mutations occasionally appear either in natural populations of Drosophila melanogaster or in P-M hybrid dysgenesis. We found that they may be reproducibly obtained with a high frequency from crosses between males from the % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaubiaeqale% qabaWaaubiaeqameqaleaacaGGQaaaoeaacaWGHbGaam4raaaaa0qa% aiaadEhaaaaaaa!3A01!\[\mathop w\nolimits^{\mathop {aG}\nolimits^* } \] strain and females from the w ^aG* strain or its derivatives. Super-unstable mutations in the ocelliless, singed, white, yellow and other loci have been obtained. Each super-unstable mutation gives rise to a large family of new super-unstable mutations with a wide range of phenotypic expression. Mutations with the same phenotype often differ in the specificity of their potential for further mutation. As a rule, a super-unstable mutation is associated with a specific reversible mutation and paired alleles are formed in this way. Other mutations are usually irreversible, but new mutations of these may also form paired alleles. Active transposase encoded by transposable P elements is necessary to maintain super-instability. Finally, some preliminary molecular data are discussed which suggest that this type of super-instability is a result of interaction between P elements and a novel mobile element, designated as X.     

Hybrid dysgenesis in Drosophila melanogaster: influence of temperature on cytotype determination in the P-M system

Summary In Drosophila melanogaster, the P-M system of hybrid dysgenesis is a syndrome of germ line abnormalities, including temperature dependent gonadal dysgenesis (GD sterility), high rates of mutation and male recombination, which occurs in some interstrain hybrids but only from one of the two crosses. In the P-M system, hybrid dysgenesis results from interaction between chromosomally transposable elements of the P element family and a particular extrachromosomal state referred to as the M cytotype. Cytotype (M or P) is known to be determined by the absence or presence of chromosomal factors, but principally with limited cytoplasmic transmission.In a series of experiments in which F1 hybrid females from various P and M strains were submitted to different preadult and ageing temperature treatments, it was found that the cytotype switch is strongly temperature-dependent in the F1 females from M x P but not in the reciprocal cross. In the F1 females from the former cross, a strong M cytotype occurs at a low developmental temperature (18° C) and a weak M cytotype occurs at a high developmental temperature (26.5° C). On the other hand, a high ageing temperature applied after a low developmental temperature switches the cytotype from M to P and reciprocally, a low ageing temperature applied after a high developmental temperature switches the cytotype from P to M.This thermo-reversibility of the extrachromosomal state exists only in the F1 females from M mothers but not in the F1 females from P mothers; this dissymmetrical behavior is discussed in relation to the mechanism proposed by O'Hare and Rubin (1983) which explains cytotype determination by a positive feedback of the regulator of the P transposase on its own level of activity.     

P-M hybrid dysgenesis affects juvenile hormone metabolism in Drosophila melanogaster females

This paper studies the metabolism of the juvenile hormone, which affects gonads functioning in Drosophila melanogaster females under P-M hybrid dysgenesis. It is shown that dysgenic females grown at 29°C have increased levels of the juvenile hormone (its degradation and stress reactivity are reduced), which apparently is a compensatory response to ovarian hypoplasia.     

Genetic and molecular analysis of repression in the P-M system of hybrid dysgenesis in Drosophila melanogaster.

Twelve inbred lines derived from an M' strain of Drosophila melanogaster were used to study the repression of P-element-mediated hybrid dysgenesis. Initial assessments indicated that the lines differed in the ability to repress gonadal dysgenesis, and that this ability was highly correlated with the ability to repress snw hypermutability. Later assessments indicated that most of the lines with low or intermediate repression potential evolved to a state of higher repression potential; however, Southern analyses failed to reveal significant changes in the array of genomic P elements that could account for this evolution. In addition, none of the lines possessed the incomplete P element known as KP, which has been proposed to explain repression in some D. melanogaster strains. One of the lines maintained intermediate repression potential throughout the period of study (52 generations), indicating that the intermediate condition was not intrinsically unstable. Genetic analyses demonstrated that in some of the lines, repression potential was influenced by factors that were inherited maternally through at least two generations; however, these factors were not as influential as those in a classic P cytotype strain. Additional tests with a dysgenesis-inducing X chromosome called T-5 indicated that repression itself was mediated by a combination of maternal effects and paternally inherited factors that were expressed after fertilization. These tests also suggested that in some circumstances, the P transposase, or its message, might be transmitted through the maternal cytoplasm.     

Hybrid dysgenesis in Drosophila melanogaster: a new type of gonadal dysgenic sterility expressed at the pre-pupal stage

Two sublines, B-202 and B-207, which were derived from crosses between Or-R (M) females and Cy/Pm (P) males were found to cause a new type of gonadal dysgenic sterility, designated as the GD-3. GD-3 sterility showed a typical reciprocal cross effect under the P-M system. It was caused at the frequency close to 100% in dysgenic offsprings reared above 25 degrees C, of which gonads were morphologically clearly different from those of usual GD sterility, whereas there was no indication of GD-3 sterility at temperatures below 24 degrees C. Temperature sensitive period of GD-3 sterility was estimated to the prepupal stage by shift-down experiment. In the B-202 subline, the 2nd chromosomes marked with Pm alone carried GD-3 elements. Those of the B-207 subline, however, were estimated to locate both on the 2nd and 3rd chromosomes, acting synergistically with each other.     

Phenotypic stability of the P-M system in wild populations of Drosophila melanogaster

The P element appears to be one of the most recently invaded transposons of D. melanogaster. To study the dynamics and long-term fate of P elements in natural populations of D. melanogaster, 472 isofemale lines newly collected from 27 localities of Japan were examined for the P element-associated characteristics (abilities to induce and repress of P element transposition) and genomic P element composition (size classes and their numbers). There was variation in the P element-related phenotypes among local populations, but genomic P composition did not correlate strongly with the phenotype of each line: full-size P and KP elements predominated in their genomes (FP+ KP predominance). Comparison with previous results suggests a stability in the P-M system in local populations over about 15 years. In some populations, phenotypic stability for particularly long times was found: for 30 years or more Q strains predominated in Hikone and Tanushimaru, P or Q strains around Inakadate, and M' or Q strains around Tozukawa. There was no clear evidence of structural destruction underlying functional variation of P elements during this period. These results suggest that the current evolutionary status of P elements in the gene pool of D. melanogaster is not intermediary stage predicted by the original recent invasion hypothesis, and that several other factors such as the position effect play important roles.     

Germline autonomous sterility of P-M dysgenic hybrids and their application to germline transfers in Drosophila melanogaster

The gonadal (GD) sterility of the P-M hybrid dysgenesis of Drosophila melanogaster was analyzed with reciprocal pole cell transfers. GD sterility was found to result from autonomous degeneration of germline cells; the death of individual germline cells could not be prevented by the surrounding tissues of nondysgenic flies. Germline cells of the M strains developed predominantly in the hybrid-dysgenic flies even at a low rate of GD sterility. The autonomous ability of germ plasm to induce functional germ cells was confirmed using hybrid-dysgenic hosts for transferring ectopically formed pole cells. The advantages of germline transfers using the hybrid-dysgenic hosts are discussed.     

Visible mutations induced by P-M hybrid dysgenesis in Drosophila melanogaster result predominantly from P element insertions.

This study supplied no evidence that P-M hybrid dysgenesis is a general release mechanisms for transposon movement. Newly induced mutations (23 singed, three yellow, and one white) were generated by hybrid dysgenesis and were molecularly analyzed for the presence or absence of P element insertions. Only one dysgenically-induced insertion mutation out of 27 analyzed was the result of a non-P insert; this frequency is not statistically above the non-dysgenic control level. Thus, it appears that individual transposable elements families are independently regulated.     

Developmental studies of lethality associated with the antennapedia gene complex in Drosophila melanogaster

A number of dominant homoeotic mutations are localized to the proximal right arm of chromosome 3 of Drosophila melanogaster and are thought to represent members of a gene complex that controls normal determinative decisions in the head and thorax. We have designated this complex the Antennapedia gene complex (ANT-C). Developmental studies were done to investigate the nature of the lethality associated with members of two of the complementation groups within ANT-C. The first complementation group, represented by the mutant Multiple Sex Combs (Msc) is characterized by embryonic lethality when heterozygous with a deletion of the ANT-C. The second complementation group consists of Antennapedia (Antp), Antennapedia-Extra Sex Combs (Antp^Scx), and the lethals recovered as revertants of Antp^Ns. When heterozygous for a deletion of the ANT-C or in heterozygous condition with each other, the members of this group show effective lethal phases spanning from embryo-larval boundary to late larval stages. Wakimoto and Kaufman (1981) show that the Antp⁺ gene acts to establish normal determinative states in the thorax. In the present work, transplantation of eye-antennal disks from lethal individuals heterozygous for two different Antp^Ns revertant chromosomes into wild-type hosts allowed the assessment of the function of the Antp⁺ allele in the antenna. Since these transplants formed only antennal structures and showed no evidence of the antennal → leg transformation seen in Antp^Ns controls, we conclude that the wild-type function of the Antp locus is not necessary for the establishment and/or maintenance of the antennal determined state. We suggest that regulatory mechanisms associated with the Antp⁺ structural gene normally function both to allow its expression in the thorax and to repress it in the antenna.     

The synergistic effect of X-rays and deficiencies in DNA repair in P-M hybrid dysgenesis in Drosophila melanogaster.

X-rays and deficiencies in DNA repair had a synergistic effect on genetic damage associated with P-element mobility in Drosophila melanogaster. These interactions, using sterility and fecundity as endpoints, were tested in dysgenic males deficient in either excision or post-replication DNA repair. Three sublines of the Harwich P strain were used for the construction of hybrid males. These sublines differ in P-induction ability based on gonadal dysgenesis sterility (GD) and snw mutability tests, in P-element insertion site pattern, and in the types of defective P-elements, such as KP elements, they possess. A lower degree of gonadal dysgenesis was correlated with the presence of KP elements. GD sterility and snw mutability were not always correlated. Dysgenic hybrids originating from the standard reference subline, Harwich(white), were much more sensitive to the post-replication repair than the excision repair defect. In contrast, sterility of hybrids derived from the weak subline was least affected by, and that of hybrids of the strongest subline was most affected by either DNA repair deficiency. The exacerbation by X-rays of the effects of DNA repair deficiencies on genetic damage indicates that both repair mechanisms are required for processing DNA lesions induced by the combined effect of P activity and ionizing radiation.     

Characteristics of inserted mutations obtained in the P-M hybrid dysgenesis system in the 9F12-10A7 region of the Drosophila melanogaster X-chromosome

19 new mutations in the 9F12-10A7 region of Drosophila melanogaster X chromosome was obtained in the system of P-M hybrid dysgenesis. They appeared to be lethals, as judged from viability of homo- or hemizygous females. In situ hybridization of P DNA with polytene chromosomes revealed P-element insertion in the 10A1-2 band in the majority of the mutants. As a result of complementation analysis, all these mutations were localized at previously known loci: l(1)BP1, l(1)BP5, l(1)BP8, l(1)BP7. No insertion mutations were found at the vermilion locus. This can imply for non-random distribution of insertion mutations in the region studied. Further comparison of these mutations with previously EMS-induced ones revealed that insertion mutations are predominantly hypomorph lethals which do not influence the viability, morphology and fertility of homozygous males and females, but drastically reduce viability of hemizygous females.