Graduation Year

2026

Date of Submission

12-2025

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

W.M. Keck Science Department

Second Department

Biology

Reader 1

Ethan Van Arnam

Reader 2

Serine Avagyan

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Terms of Use for work posted in Scholarship@Claremont.

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© 2025 Jisue Choi

Abstract

The epigenetic regulator ASXL1 is frequently mutated in aging human hematopoiesis, yet its role during the earliest stages of T-cell development remains unclear. Using the zebrafish model, we tested whether asxl1 loss influences the developmental T-cell program. One-cell–stage zebrafish embryos were injected with CRISPR–Cas9 ribonucleoprotein complexes targeting asxl1 or control gene znf646p, and thymic rag1 expression was assessed at 5 days post-fertilization by whole-mount in situ hybridization. Across 13 clutches (control, n = 98; asxl1, n = 117), asxl1-targeted embryos consistently exhibited a higher proportion of strong thymic rag1 expression compared with controls (62% versus 49%). Although this difference did not reach statistical significance, the directional shift was reproducible in biologically independent groups. Targeted asxl1 amplicon sequencing confirmed CRISPR mutagenesis with variable mosaicism, and the trend toward increased rag1 expression persisted when analyses were restricted to genotypically validated edited embryos (asxl1, n = 48, 58% versus 42%). These findings suggest that asxl1 loss may promote elevated thymic rag1 expression during early T-cell development, consistent with a model in which asxl1 normally constrains premature activation of lymphoid gene programs. While variability in injection quality, mosaic editing, and early-stage procedural inconsistency likely reduced sensitivity, the observed trend aligns with known roles for asxl1 in regulating lineage fidelity through chromatin-based mechanisms. This study provides initial in vivo evidence for an asxl1-dependent effect on early thymic gene expression and establishes a framework for follow-up experiments using stable mutant lines and broader transcriptional profiling.

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