pitkin^D, a Novel Gain-of-Function Enhancer of Position-Effect Variegation, Affects Chromatin Regulation During Oogenesis and Early Embryogenesis in Drosophila

Corresponding author: Gunter Reuter, Institute of Genetics, Martin Luther University, D-06120 Halle, Weinbergweg 10, Germany., reuter{at}genetik.uni-halle.de (E-mail)

Communicating editor: T. C. KAUFMAN

The vast majority of the >100 modifier genes of position-effect variegation (PEV) in Drosophila have been identified genetically as haplo-insufficient loci. Here, we describe pitkin^Dominant (ptn^D), a gain-of-function enhancer mutation of PEV. Its exceptionally strong enhancer effect is evident as elevated spreading of heterochromatin-induced gene silencing along euchromatic regions in variegating rearrangements. The ptn^D mutation causes ectopic binding of the SU(VAR)3-9 heterochromatin protein at many euchromatic sites and, unlike other modifiers of PEV, it also affects stable position effects. Specifically, it induces silencing of white⁺ transgenes inserted at a wide variety of euchromatic sites. ptn^D is associated with dominant female sterility. +/+ embryos produced by ptn^D/+ females mated with wild-type males die at the end of embryogenesis, whereas the ptn^D/+ sibling embryos arrest development at cleavage cycle 1–3, due to a combined effect of maternally provided mutant product and an early zygotic lethal effect of ptn^D. This is the earliest zygotic effect of a mutation so far reported in Drosophila. Germ-line mosaics show that ptn⁺ function is required for normal development in the female germ line. These results, together with effects on PEV and white⁺ transgenes, are consistent with the hypothesis that the ptn gene plays an important role in chromatin regulation during development of the female germ line and in early embryogenesis.

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