Maternal transmission of P element transposase activity in Drosophila melanogaster depends on the last P intron

Abstract

Maternal transmission of RNAs or proteins through the egg cytoplasm plays an important role in eukaryotic development. We show that the transposase activity encoded by the P transposable element of Drosophila melanogaster is transmitted through the oocytes of females heterozygous for this element even when these oocytes do not carry the element itself. However, this maternal transmission is abolished when the last of three introns is removed from the P element. These facts imply that maternal transmission of transposase activity involves the RNA transcribed from the P element rather than the polypeptide it encodes, and that to be transmitted maternally, this RNA must possess the last intron. Examination of the intron's sequence reveals that it contains a motif of nine nucleotides that has been implicated in the maternal transmission of developmentally significant RNAs. This same intron limits expression of the P transposase to the germ line of Drosophila. Thus, the last P intron has two important biological functions.D NA sequencing projects have revealed a plethora of transposable elements in the genomes of different organisms (1). Among these transposons, the P elements of the fruit fly Drosophila melanogaster are among the best understood and technologically most useful (2). P elements have been widely used as insertional mutagens to tag genes for cloning, and as vectors for the genetic transformation of Drosophila. These applications have become paradigms for the use of transposons as genetic tools in other organisms.P elements are found in natural populations, but not in long-standing laboratory stocks, apparently because they invaded the D. melanogaster genome sometime in the middle of the 20th century (3, 4). These elements were discovered through their involvement in a syndrome of germ-line abnormalities called hybrid dysgenesis (5). These abnormalities include high frequencies of mutation, chromosome breakage, and sterilityall caused by P element excision and transposition in the germ-line cells. The traits of hybrid dysgenesis occur in the offspring from crosses between males that carry P elements in their genomes and females that do not, but usually not in the offspring from the reciprocal cross. This difference between genetically identical offspring indicates that hybrid dysgenesis is repressed by a maternally inherited condition associated with the P elements. This condition, called the P cytotype (6), is thought to arise from some product(s) of the P elements themselves. In most models, these products are hypothesized to pass from mother to offspring through the egg cytoplasm (2, 7).When P elements are introduced into laboratory stocks via crosses, they transpose in the germ line but not in the somatic tissues. This tissue-specific behavior is caused by the synthesis of a P-encoded enzyme, an 87-kDa transposase that catalyzes P excision and transposition, in germ-line cells only (8). In somatic cells, the last of the three introns in the transposase gene is not spliced out of the P element's RNA. ...

The recent invasion of natural Drosophila simulans populations by the P-element

“…Genomic barriers to the establishment of P-element in D. simulans might have been overcome by adaptation of the TE to D. simulans. The single substitution distinguishing the D. melanogaster and D. simulans P-element seems unlikely to confer a functional advantage: It occurs in an intron and does not coincide with characterized splicing motifs (6,44) or with the 9-bp motif responsible for maternal transmission (45). Instead, our observations suggest that successful horizontal transmission of the P-element is rare.…”

Insect Population Control by Homing Endonuclease-Based Gene Drive: An Evaluation inDrosophila melanogaster

“…Rong and coworkers observed that the ratio of HR events to illegitimate events was sixfold better in females than in males (Rong and Golic 2000). Indeed, since Act5C-P-HEG transmits maternal HEG transcripts to progeny that do not have a donor template available, HEG activity in these progeny can resolve only as extraneous NHEJ events in our assay (Simmons et al 2002). Since we cannot distinguish between NHEJ events arising in the oocyte and those arising through maternally derived HEG activity in the progeny, the rate of cutting in the oocyte is almost certainly overstated and the true rate of homing within the oocyte is higher than the 50% we report in Table 1.…”

Paternally and maternally transmitted GAL4 transcripts contribute to UAS transgene expression in early Drosophila embryos

“…To find clues that could, at least in part, provide a molecular explanation for the described parental Gal4 transmission, we searched the sequences of the fragments used upstream of the Gal4 gene in p[GawB], but we did not identify a common motif, which may have explained their expression pattern. However, transcripts from the P-element borne transposase have also been shown to be maternally contributed to oocytes and may contribute to the P cytotype effect (Engels, 1979;Simmons et al, 2002). In this case, as for other maternally provided RNAs (bicoid and nanos), it appears that the consensus motif YTGTTYCTG (Y is any nucleotide), mediates efficient RNA transport into the developing oocytes (Gottlieb, 1992;Simmons et al, 2002).…”