Tag: Bio-Zebrafish and DNA

Investigating the role of H3K9 methyl transferases in heat-induced DNA damage

Presenter: Philip Nosler – Biology

Faculty Mentor(s): Nicole Kurhanewicz, Diana Libuda

Session: (In-Person) Oral Panel—Bio-Zebrafish and DNA

Exposure to elevated temperature is a major cause of male infertility observed across both animals and plants. A primary consequence of heat stress is the accumulation of unusually high levels of DNA damage in developing sperm. Previous work from the Libuda Lab demonstrated that, similarly to humans, a single acute heat exposure is sufficient to produce high levels of DNA damage in developing sperm, but not in developing eggs in the model organism Caenorhabditis elegans. Further, mobilization of transposons, segments of DNA that can move autonomously throughout the genome, was associated with heat-induced DNA damage specifically in sperm. Normally, transposon movement is strictly repressed in the germline via chromatin modifications, which affect chromosome structure and regulate gene expression. Specifically, transposon genes are silenced in the germline via a particular chromatin modification: methylation of histone H3 lysine 9 by the methyltransferases SET-25, SET-32, and MET-2. Using an existing mutant strain for set-25 and a double mutant for met- 2;set-25, I found that DNA damage is elevated following heat stress, suggesting set-25 and met-2 repress heat-induced DNA damage. Currently, I am further assessing the roles of set-25, set-32, and met-2 in heat-induced DNA damage using single and double mutant strains. Overall, this work will further our understanding of the mechanisms underlying heat-induced male infertility.

Urotensin-II-related peptides, Urp1 and Urp2, control zebrafish spine morphology

Presenter: Colin Kuhns − Psychology

Faculty Mentor(s): Elizabeth Bearce

Session: (In-Person) Oral Panel—Bio-Zebrafish and DNA

The spine is the defining feature of vertebrate life. The morphology of the vertebral column emerges in animals during embryogenesis and continues to develop into adulthood. Motile cilia, beat back and forth on the surface of cells to generate microscopic fluid flows. The generated fluid flow is essential both for the initial generation of a linear body and for the maintenance of a linear spine. Urotensin-II-related peptides (URP), Urp1 and Urp2, are 10-amino acid cyclized peptides and are expressed in flow-sensory neurons in the central canal. Previous findings have hypothesized a model in which Urp1 and Urp2 promote the axial straightening downstream of motile cilia function through inducing contraction of dorsal muscles. However, it has remained unknown whether Urp1 and/or Urp2 also function beyond embryogenesis in the maintenance of spine morphology during growth. Here we show that Urp1 and Urp2 are in fact dispensable for axial straightening during embryonic and early larval phases, contradicting the current model. Instead, we found that Urp1/Urp2 are essential for maintaining spinal linearity during later growth phases, with clear spinal dysmorphology in mutants during juvenile growth. Curves induced upon loss of Urp1/Urp2 model aspects of kyphosis and are distinct from curves exhibited by cilia motility mutants. Overall, this work links Urotensin peptide signaling to spine morphology and provides a new animal model for the common human spine dysmorphology of kyphosis.

Mechanisms of 3D genome organization by condensin and its interactors

Presenter(s): Yukiko Gaudreault — Biology

Faculty Mentor(s): Osamu Iwasaki

Session: Oral Panel—Bio-Zebrafish and DNA

It is known that eukaryotic genomes are organized in differently sized chromatin domains, including topologically associating domains (TADs) which organize active and inactive chromatin domains and therefore coregulate transcription. This structure is of great interest because when defective, it can lead to developmental abnormalities and human disease. The in situ Hi-C method has been applied to fission yeast cells to show that the protein complex condensin forms ~500kbp chromosomal domains that are required for proper chromosome segregation during mitosis. However, it is still unclear how condensin domains are formed and regulated during the cell cycle. Here we show several potential condensin interactors involved in the regulation of condensin-mediated domains. To do so, we applied the auxin-inducible degron system to 9 condensin interactor genes that were previously found via yeast-two hybrid screening. Performing in situ Hi-C on these conditional knock-out strains showed that Clc1/ clathrin and Sds3/ histone deacetylase promote the formation of condensin domain and that Fyu1/ UTP-glucose-1-phosphate uridylyltransferase and Pfk1/ 6-phosphofructokinase negatively regulate condensin function. We anticipate these results to drive further investigation into the involvement of metabolic proteins in genome organization, as well as the further understanding of chromosome organization mediated by condensin and its interactors.

A Novel Zebrafish Mutant Reveals New Insight into Cilia Motility Regulation and Body Axis Formation

Presenter: Craig Samuel — Biology

Faculty Mentor(s): Daniel Grimes, Zoe Irons

Session: (In-Person) Oral Panel—Bio-Zebrafish and DNA

Motile cilia are responsible for critical functions in development, including left-right patterning and cerebrospinal fluid flow. Their motility depends on the assembly of outer dynein arms: ATPases which power ciliary beating. Defects in dynein arm function occur in Primary Ciliary Dyskinesia, a disorder affecting 1:15,000–30,000 human births. Daw1 is a cytoplasmic protein thought to be required for cilia beating by controlling import of dynein arms into cilia. Here, I use zebrafish as a model to understand Daw1 function during development and growth. I characterize daw1b1403 mutants, a new daw1 mutant line harboring a 2-amino acid deletion in a conserved region of the protein generated by CRISPR mutagenesis. Defects associated with motile cilia dysfunction in daw1b1403 mutants, including otolith abnormalities, left-right patterning defects, and abnormal body axis curvature are observed. Surprisingly, daw1b1403 mutants exhibit recovery of body curve defects later in development. Consequently, we hypothesize that Daw1 is not essential for cilia motility per se, but only for timely onset of beating over developmental timescales. Importantly, this Daw1 model of delayed cilia motility and body straightening provides an opportunity to study how early embryos can sense, or correct, shape deformations, which is an exciting and relatively unknown aspect of developmental morphogenesis. Ultimately, understanding these processes may help inform our treatments of congenital disorders.