Chip physically interacts with Notch and their stoichiometry is critical for Notch function in wing development and cell proliferation in Drosophila

Notch and LIM-homeodomain protein Arrowhead regulate each other in a feedback mechanism to play a role in wing and neuronal development in Drosophila

The Notch pathway is an evolutionarily conserved signalling system that operates to influence an astonishing array of cell fate decisions in different developmental contexts. To identify novel effectors of Notch signalling, we analysed the whole transcriptome of Drosophila wing and eye imaginal discs in which an activated form of Notch was overexpressed. A LIM-homeodomain protein, Arrowhead (Awh), was identified as a novel candidate that plays a crucial role in Notch-mediated developmental events. Awh alleles show strong genetic interaction with Notch pathway components. Awh loss-of-function upregulates Notch targets Cut and Wingless. Awh gain-of-function downregulates Notch targets by reducing the expression of the ligand Delta. Consequently, the expression of the Wingless effector molecule Armadillo and its downstream targets, Senseless and Vestigial, also gets downregulated. Awh overexpression leads to ectopic expression of engrailed, a segment polarity gene in the anterior region of wing disc, leading to patterning defects. Additionally, Notch gain-of-function-mediated neuronal defects get significantly rescued with Awh overexpression. Activated Notch inhibits Awh activity, suggesting a regulatory loop between Awh and Notch. Additionally, the defects caused by Awh gain-of-function were remarkably rescued by Chip, a LIM interaction domain containing transcriptional co-factor. The present study highlights the novel feedback regulation between Awh and Notch.

Notch signalling: multifaceted role in development and disease

Notch pathway is an evolutionarily conserved signalling system that operates to influence an astonishing array of cell fate decisions in different developmental contexts. Notch signalling plays important roles in many developmental processes, making it difficult to name a tissue or a developing organ that does not depend on Notch function at one stage or another. Thus, dysregulation of Notch signalling is associated with many developmental defects and various pathological conditions, including cancer. Although many recent advances have been made to reveal different aspects of the Notch signalling mechanism and its intricate regulation, there are still many unanswered questions related to how the Notch signalling pathway functions in so many developmental events. The same pathway can be deployed in numerous cellular contexts to play varied and critical roles in an organism's development and this is only possible because of the complex regulatory mechanisms of the pathway. In this review, we provide an overview of the mechanism and regulation of the Notch signalling pathway along with its multifaceted functions in different aspects of development and disease.

Somatic Clonal Analyses Using FLP/FRT and MARCM System to Understand Notch Signaling Mechanism and Its Regulation

Notch signaling regulates an array of developmental decisions and has been implicated in a multitude of diseases, including cancer over the past a few decades. The simplicity and versatility of the Notch pathway in Drosophila make it an ardent system to study Notch biology, its regulation, and functions. In this chapter, we highlight the use of two powerful techniques, namely, FLP/FRT and MARCM in the study of Notch signaling. These mosaic analysis techniques are powerful tools to analyze gene functions in different biological processes. The section briefly explains the principle and the protocols with suitable examples.