טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBoico Olga
SubjectThe Role of dHey, a Transcriptional Repressor, during
Drosophila Development
DepartmentDepartment of Medicine
Supervisor Professor Amir )Oryan )Orian


Abstract

Transcription factors are required to execute temporally coordinated gene expression programs that are essential for many physiological and developmental processes. In this regard, of specific interest are the identification of context-specific transcriptional programs, and the characterization of the proteins networks that regulates these programs. In this study I focused on dHey, an atypical member of the HES family of transcriptional repressors that in part acts downstream to Notch signaling pathway. I hypothesized that despite the many similarities, dHey exhibits several structural differences from other HES repressors that may result in unique biological functions. Moreover, I hypothesized that dHey has both, Notch-dependent as well as Notch-independent functions.

First, using DamID profiling, I mapped the genomic loci bound by dHey genome wide in Drosophila K167 cells. In addition, I determined the role of dHey within the context of the Notch signaling pathway. Using bioinformatics analysis and dHey binding data I found that while a significant portion (25%) of Notch regulated genes are directly bound by dHey, these genes represent only 14% of the overall genomic loci bound by dHey, thus suggesting for a yet unexplored Notch-independent targets and function/s.

In the second part of my work and using the adult gut as a model system I characterized Notch-dependent and Notch-independent roles of dHey in adult gut homeostasis. I found that dHey is expressed throughout the entire gut cell lineage while the dHey promoter is required for its expression in the stem cell niche. Furthermore, dHey and Notch are important within entoroblasts (EB) to enable niche exit and EB differentiation to differentiated entrocytes (ECs). In addition, in fully differentiated EC cells dHey is key to maintain the differentiated state. This function of dHey is likely Notch- independent. 

To determine the transactional program regulated by dHey in the gut I developed a surface-marking enrichment method that enables cell-specific genomic studies. Using this method I determined the transcriptional program of EB differentiation to EC, and characterized the transcriptional impact of dHey in specific cell populations. Importantly, these studies established that conditional reduction of dHey specifically in fully differentiated enterocytes (ECs) results in de-differentiation, and ectopic expression of various genomic dormant programs.

Thus, collectively these genetic and genomic analyses suggest that dHey is a context-specific transcriptional regulator that is essential for maintaining the differentiated state, plays a key role in adult Drosophila gut homeostasis.