Genetic and molecular analysis of repression in the P–M system of hybrid dysgenesis inDrosophila melanogaster

Abstract

SummaryTwelve 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.

Distribution and structure of cloned P elements from theDrosophila melanogasterP strain π2

“…1). Elements other than KP can partially repress hybrid dysgenesis (Heath & Simmons, 1991;Raymond et al 1991), but their structures have not been precisely defined.…”

“…However, other strains with KP elements did not repress hybrid dysgenesis (Simmons et al 1990;Biemont et al 1990) and some P-cytotype strains did have KP elements (Monastirioti et al 1988). Partial repression of hybrid dysgenesis has also been reported for strains with no KP elements (Heath & Simmons, 1991;Raymond et al 1991). Differences in the number, structures and locations of P elements appear to be responsible for the strain dependent regulation of hybrid dysgenesis.…”

Transcription of the singed-weak mutation of Drosophila melanogaster: elimination of P-element sequences by RNA splicing and repression of singed transcription in a P genetic background

“…Furthermore, the regulatory eVects of these repressor elements can be detected in somatic tissues, whereas regulation by cytotype is conWned to the germ-line. The production of repressor P-polypeptides appears to depend on the genomic positions of the elements that encode them (Simmons et al 1987;Biemont et al 1990;Heath and Simmons 1991;Misra et al 1993;Corish et al 1996) and the P-element promoter is known to be strongly inXuenced by Xanking sequences (O'Kane and Gehring 1987). The three positions where singed RNA 3Ј ends have been mapped are shown by downwards arrows.…”

Genetic evidence for repression of somatic P element movements in Drosophila melanogaster consistent with a role for the KP element

“…Some strong P strains, showing no chromosomally-inherited repression, contain large numbers of KP elements (Monastirioti et al, 1988). Other strains, with high levels of chromosomafly-cletermined repression, lack KP elements (Heath & Simmons, 1991). A survey of the repressing properties of single deleted P elements (Rasmusson et a!., 1993) showed that although two of the three KP elements tested repressed singef" reversion in the presence of a P transposase source, and a similar length P sequence did not, the strongest repression was elicited by a much rarer and shorter element, called SP.…”