All ETDs from UAB

Advisory Committee Chair

John M Parant

Advisory Committee Members

Mary Ann Bjornsti

Alecia Gross

Michael Miller

John Shacka

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

INVESTIGATING PHENOTYPIC SEVERITY ASSOCIATED WITH SISTER CHROMATID COHESION DEFECTS IN HUMAN DISEASE STEFANIE M. PERCIVAL GRADUATE BIOMEDICAL SCIENCES ABSTRACT Sister chromatid cohesion (SCC) is a process that utilizes a proteinaceous ring, cohesin, for accurate chromosome segregation. An essential process in S phase termed cohesion establishment is necessary to stabilize cohesin rings around sister chromatids. Mutations in establishment of cohesion homolog 2 (ESCO2), a protein essential for cohesion establishment, cause a developmental disorder called Roberts Syndrome (RBS). Cytogenetic analysis in patients reveals heterochromatic repulsion (HR), a centromeric puffing, indicative of cohesion defects. The severity of phenotypes varies from preterm lethal to mild phenotypes into adulthood. Animal models investigating SCC are often embryonic lethal, limiting cellular analysis. To overcome these obstacles, we use zebrafish to take advantage of their ex vivo fertilization and transparent tissue during embryogenesis. Because mutations in SCC often lead to improper chromosome segregation, we first developed an assay to observe mitosis in a live zebrafish embryo to determine the extent and outcomes of these mitotic defects. Utilizing this assay, we characterize an embryonic lethal esco2 mutant zebrafish and find that lethality is due to complete cohesion loss, chromosome missegregation, genomic instability, and apoptosis. Surprisingly, a subset of cells overcomes Esco2 loss, displays mild cohesion defects, and divides normally indicating a possible compensation mechanism exists. Esco2 heterozygous embryos are viable and exhibit a weakened cohesion phenotype similar to the HR in RBS. Interestingly, esco2 heterozygous animals have enhanced tumor onset in a predisposed model system. The variation in disease phenotype and cohesion defects between homozygous and heterozygous embryos suggest a gene dose effect of Esco2 that impacts the extent of phenotypic severity. To further understand how cohesion establishment impacts cellular and organismal viability, we employ genome editing technology to generate mutants in establishment of cohesion homolog 1 (Esco1), Shugoshin-Like 1 (SgoL1), and Sororin (Cell division cycle-associated protein 5, Cdca5) due to their involvement in cohesion establishment and maintenance. Though all are lethal in cell culture, we observe a phenotypic spectrum in severity at the gross morphology level that strongly correlates to their severity in cohesion defects. This has significant implications in understanding the variable phenotypes associated with RBS, other cohesinopathies, and disorders associated with cohesion defects.

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