ALBERT

Description: Previous studies have shown that telomeric P elements inserted at the left end of the X chromosome are anchors of the P cytotype, the maternally inherited state that regulates P -element activity in the germ line of Drosophila melanogaster . This regulation is mediated by small RNAs that associate with the Piwi family of proteins (piRNAs). We extend the analysis of cytotype regulation by studying new combinations of telomeric and nontelomeric P elements ( TP s and non- TP s). TP s interact with each other to enhance cytotype regulation. This synergism involves a strictly maternal effect, called presetting, which is apparently mediated by piRNAs transmitted through the egg. Presetting by a maternal TP can elicit regulation by an inactive paternally inherited TP , possibly by stimulating its production of primary piRNAs. When one TP has come from a stock heterozygous for a mutation in the aubergine , piwi , or Suppressor of variegation 205 genes, the synergism between two TP s is impaired. TP s also interact with non- TP s to enhance cytotype regulation, even though the non- TP s lack regulatory ability on their own. Non- TP s are not susceptible to presetting by a TP , nor is a TP susceptible to presetting by a non- TP . The synergism between TP s and non- TP s is stronger when the TP was inherited maternally. This synergism may be due to the accumulation of secondary piRNAs created by ping-pong cycling between primary piRNAs from the TP s and mRNAs from the non- TP s. Maternal transmission of P -element piRNAs plays an important role in the maintenance of strong cytotype regulation over generations.