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Updated: Jan 24, 2026

Multi-target Chromogenic Whole-mount In Situ Hybridization for Comparing Gene Expression Domains in Drosophila Embryos
Published on: January 31, 2016
Bivalency in Drosophila embryos is associated with strong inducibility of Polycomb target genes
Arslan Akmammedov1, Marco Geigges1, Renato Paro1,2
1Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland.
Abstract:
Polycomb group (PcG) and Trithorax group (TrxG) proteins orchestrate development of a multicellular organism by faithfully maintaining cell fate decisions made early in embryogenesis. An important chromatin mark connected to PcG/TrxG regulation is bivalent domains, the simultaneous presence of H3K27me3 and H3K4me3 on a given locus, originally identified in mammalian embryonic stem cells but considered to be absent in invertebrates. Here, we provide evidence for the existence of bivalency in fly embryos. Using a recently described PcG reporter fly line, we observed a strong reporter inducibility in the embryo and its sharp decrease in larval and adult stages. Analysis of the chromatin landscape of the reporter revealed a strong signal for the repressive PcG mark, H3K27me3, in all three developmental stages and, surprisingly, a strong signal for a transcriptionally activating H3K4me3 mark in the embryo. Using re-chromatin immunoprecipitation experiments, bivalent domains were also uncovered at endogenous PcG targets like the Hox genes.
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Titration Calculations: Strong Acid - Strong Base
A titration is carried out for 25.00 mL of 0.100 M HCl (strong acid) with 0.100 M of a strong base NaOH. The pH at different volumes of added base solution can be calculated as follows:
(a) Titrant volume = 0 mL. The solution pH is due to the acid ionization of HCl. Because this is a strong acid, the ionization is complete and the hydronium ion molarity is 0.100 M. The pH of the solution is then:
Strong Acid and Base Solutions
Titration of a Strong Acid with a Strong Base
Titration Calculations: Weak Acid - Strong Base
For the titration of 25.00 mL of 0.100 M CH3CO2H with 0.100 M NaOH, the reaction can be represented as:
Titration of a Weak Acid with a Strong Base
Titration of Polyprotic Acids with a Strong Base

