Understanding the temporal patterning process of the Drosophila medulla by identification of a complete cascade and the cisregulatory elements of temporal transcription factors

During development, neural progenitors are temporally patterned to sequentially generate a variety of neural types. In Drosophila neural progenitors called neuroblasts, temporal patterning is regulated by the sequential expression of Temporal Transcription Factors (TTFs). However, known TTFs were primarily identified through candidate approaches and may not constitute a complete cascade. In addition, many fundamental questions remain concerning the initiation, progression, and termination of the TTF cascade. In Chapter 2, single-cell RNA sequencing (scRNA-seq) was employed to the Drosophila medulla NBs to unveil novel TTFs and additional determinants. A list of novel TTF candidates crucial for medulla temporal patterning was identified. The extensive cross-regulations among the novel TTFs and known ones generally follow the rule that an earlier TTF activates a later one, while a later TTF represses an earlier one. The work described in Chapter II revealed a comprehensive temporal patterning cascade: Hth + SoxN + dmrt99B -> Opa -> Ey+Erm -> Ey+Opa -> Slp+Scro -> D -> B-H1&2->Tll, Gcm. It was also uncovered that Lola transcription factors, expressed in all NBs, modulate the speed of temporal cascade progression. In Chapter 3, single-cell sequencing assay for transposase-accessible chromatin (scATAC-seq) was employed to Drosophila larval brain cells to evaluate the dynamic changes in chromatin accessibility of the medulla NBs and to identify TTF enhancers. The scATAC-seq data unveiled putative regulatory sequences for TTFs and other genes crucial for medulla development. Putative enhancers of TTFs exhibited temporal accessibility patterns well correlated with the temporal expression profiles of TTFs in the medulla NBs. Through reporter assays, enhancers for opa, erm, ey, D, and BarH2 were identified. These TTF enhancers were able to drive GFP initiation in a temporal pattern mirroring that of wild-type TTFs in the medulla NBs. These findings lay a solid foundation for further characterization of the gene regulatory networks driving the temporal cascade progression in the medulla NBs.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Cell and Developmental Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Zhu, Hailun

Contributors dc:contributor

• Li, Xin
• Chen, Jie
• Smith-Bolton, Rachel
• Yang, Jing

• Neural Progenitor
• Temporal Patterning
• Ttf
• Drosophila

Statement dc:rights

• Copyright 2024 Hailun Zhu

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/124685

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F124685