GENOTYPIC EFFECTS, MATERNAL EFFECTS AND GRAND-MATERNAL EFFECTS OF IMMOBILIZED DERIVATIVES OF THE TRANSPOSABLE ELEMENT MARINER

The baseline rate of spontaneous integration of the autonomous mariner element Mos1 into the germline of Drosophila melanogaster is estimate d as 16 +/- 5% (mean +/- SE) among fertile GO flies. However, the tran sformation rate is reduced similar to 20-fold in Mos1 constructs with exogenous DNA in the size range 5-12 kb inserted into the SacI site. T o provide alternative Mos1 helper plasmids for transformation experime nts, two types of Mos1-promoter fusions were constructed: hsp-70:Mos1 and hsp26-Sgs3:Mos1. The former has die Mos1 coding region driven by t he hsp70 heat-shock promoter; the latter has it driven by the basal Sg s3 promoter under the control of the hsp26 female-germline specific tr anscriptional regulator. When introduced into D. melanogaster by P-ele ment-mediated germline transformation, these elements are unable to tr anspose or excise in the presence of autonomous Mos1-related elements (they are ''marooned'') because the 5' inverted repeat of Mos1 is miss ing. As expected, the hsp26-Sgs3:Mos1 fusions exhibit a significantly greater rate of germline excision of a target mariner element than do the hsp70:Mos1 fusions. Unexpectedly, the rate of excision of target m ariner elements induced by hsp26-Sgs3:Mos1 is the same in the male ger mline as in the female germline. Both hsp:Mos1 fusions show strong ger mline expression and a maternal effect of the mariner transposase. A s ignificant grand-maternal effect of the hsp:Mos1 fusions was also dete cted as a result of a maternal effect on the germline of the F-1 proge ny. Among flies carrying the promoter fusions inherited maternally, ab out three-quarters of the overall rate of germline excision derives fr om the direct genotypic effect and about one-quarter results from the grand-maternal effect. Despite the strong somatic expression of the hs p:Mos1 fusions, mariner transformants carrying a white(+) reporter gen e at the SacI site remained stable in the soma.