P element transposition is repressed when P transposase is not produced or its action is inhibited. Repression occurs by two mechanisms. First, P elements located near the X chromosome telomere are transcribed in both sense and antisense directions to initiate an RNAi-like mechanism to eliminate transposase mRNA produced by all P elements in the genome. This mechanism may also alter chromatin to repress transposition. Second, peptide repressors are produced from P element sequences that prevent P transcription or transposition. P elements with different internal sequences deleted are useful for examining both modes of P repression.
Strains that can repress the production or action of P transposase are said to have P cytotype. They are identified by "|P-cytotype|" in the genotype. Most stocks in the Bloomington collection lack P repression and, consequently, have M cytotype. Crosses between M and P strains can produce hybrid dysgenesis in progeny from mobilization of P insertions. We recommend that you familiarize yourself with P element biology before making crosses with P cytotype stocks.
See Stocks Useful for Transposable Element Mutagenesis for stocks with transgenes expressing P transposase constitutively.
Stocks with full-length P elements
These are the stocks with full-length P elements most relevant to the study of P transposition. We have ~16 other stocks with mutations or deletions produced by hybrid dysgenesis that carry autonomous P element insertions, but they are not listed on this webpage.
Stocks with "sensor" mutations for detecting P transposase or P repressor
sn[w] produces a weak “singed" bristle phenotype due to the presence of two naturally occurring, nonautonomous P insertions. Upon excision of one P element, the weak singed phenotype will change to a nearly wild type bristle phenotype. Upon excision of the other P element, the weak singed phenotype will change to a more extremely gnarled bristle phenotype.
sn[50e] produces a strong singed bristle phenotype in the absence of P repressor peptide and a weak phenotype in its presence.
Stocks with telomeric insertions of internally deleted P elements
The only P elements present in these stocks are the telomeric insertions and the P insertions associated with sn[w]. Crossing these flies to M cytotype flies will not result in hybrid dysgenesis, because the transposase genes have been disrupted. Nevertheless, these flies have P cytotype because the telomeric insertions can repress transposition of autonomous P elements.
Stocks with internally deleted P elements located at nontelomeric sites
The P elements or transgenic constructs in these stocks express P repressor constitutively or upon heat shock, but they do not express P transposase.
Papers discussing the regulation of P transposition
Engels (1989) P elements in Drosophila melanogaster. In Mobile DNA (ed. D. E. Berg and M. M. Howe), pp. 437-484. Washington, D. C.: American Society for Microbiology Publications.
Ronsseray et al. (1991) The maternally inherited regulation of P elements in Drosophila melanogaster can be elicited by two P copies at cytological site 1A on the X chromosome. Genetics 129: 501-512.
Marin et al. (2000) P-element repression in Drosophila melanogaster by a naturally occurring defective telomeric P copy. Genetics 155:1841-1854.
Stuart et al. (2002) Telomeric P elements associated with cytotype regulation of the P transposon family in Drosophila melanogaster. Genetics 162: 1641-1654.
Brennecke et al. (2008) An epigenetic role for maternally inherited piRNAs in transposon silencing. Science 322: 1387-1392.
Jensen et al. (2008) Cytotype regulation of P transposable elements in Drosophila melanogaster: repressor polypeptides or piRNAs? Genetics 179: 1785-1793.
Simmons et al. (2012) Maternal enhancement of cytotype regulation in Drosophila melanogaster by genetic interactions between telomeric P elements and non-telomeric P elements. Genet. Res. Camb. 94: 339-351.
Simmons et al. (2014) Genetic interactions between P elements involved in piRNA-mediated repression of hybrid dysgenesis in Drosophila melanogaster. Genes, Genomes, Genetics 4: 1417-1427.
Simmons et al. (2015) Transposon regulation in Drosophila: piRNA-producing P elements facilitate repression of hybrid dysgenesis by a P element that encodes a repressor polypeptide. Mol. Genet. Genomics 290: 127-140.