Analysis of biochemical mechanisms provoking differential spatial expression in Hh target genes

TL;DR

This paper investigates the biochemical mechanisms behind the spatial expression patterns of Hedgehog target genes in Drosophila, using a thermodynamic model to analyze how molecular interactions influence gene regulation.

Contribution

It introduces a thermodynamic approach to model transcription factor interactions, providing simplified formulas to analyze their effects on gene expression patterns.

Findings

High/low affinity impacts gene activation regions

Cooperation modifies repression zones

Molecular processes correlate with tissue-level features

Abstract

This work analyses the transcriptional effects of some biochemical mechanisms proposed in previous literature which attempts to explain the differential spatial expression of Hedgehog target genes involved in Drosophila development. Specifically, the expression of decapentaplegic and patched, genes whose transcription is believed to be controlled by the activator and repressor forms of the transcription factor Cubitus interruptus (Ci). This study is based on a thermodynamic approach which provides binding equilibrium weighted average rate expressions for genes controlled by transcription factors competing and (possibly) cooperating for common binding sites, in the same way that Ci's activator and repressor forms might do. These expressions are refined to produce simpler equivalent formulae allowing their mathematical analysis. Thanks to this, we can evaluate the correlation between several molecular processes and biological features observed at tissular level. In particular, we will focus on how high/low/differential affinity and null/total/partial cooperation modify the activation/repression regions of the target genes or provoke signal modulation.