Craniofacial sutures are fibrous joints which connect adjacent skull bones. The sutures are sites of growth but are probably zones of mechanical weakness compared to the bones. The suture’s ability to transmit compressive and tensile loads therefore affects both cranioskeletal growth and stress distribution. I compared tensile mechanical properties of four adjoining sutures, two longitudinal (interfrontal; n=5; internasal, n=2); and two transverse (coronal, n=2; nasofrontal, n=8). Coronal (n=6) and nasofrontal (n=1) were tested in compression. The suture specimens were extracted from the heads of young pigs used in unrelated experiments. All sutures exhibited a “toe area” where substantial strain occurred at a low load relative to the elongation. This region presumably represents the stretching of relaxed fibers. The stress-strain curve showed a linear region that began almost immediately following the toe area, in this “elastic region” the suture can recover its original length when unloaded. At high stress the response began to deviate from linearity. With further strain, the load ceases to increase, the sutures experienced plastic behavior presumably representing increased load bearing by the remaining intact fibers, when even a slight drop in force was seen. The sutures were reshaped permanently, cycles of elastic and plastic behavior continued until a final softening phase and suture failure. The mechanical properties measured were similar at all four sutures under tension and compression. Ultimate stress was variable, ranging from 0.1-4.3 MPa and an overall average of 1.32 ± 0.88 MPa (n=22). Eliminating the highest and lowest values resulted in a more accurate mean of 1.23 ± 0.54 (n=20). These values are considerably less than bone (over 100 MPa). Ultimate strain was more consistent, averaging 5.9 ± 4.3 % (range 2–14%, n=22). These values are considerably more than bone (less than 1%). Thus, sutures are more flexible but less strong than bone.

STUDIO, a near-peer STEM (science, technology, engineering, and mathematics) mentoring program, fosters growth for both the mentors and mentees. In partnership with Neighborhood House, a local multiservice community-based organization, UW mentors support low-income, immigrant and refugee youth to develop motivation, interest, and identification with STEM education and careers. Mentors do this by creating units that provide youth opportunities to learn at the intersection of their stated interests and mentor expertise. This cultivates a community of learners that values youth and mentor agency. STUDIO focuses on both mentees and mentors, but our initial research and evaluation supported by National Science Foundation has focused primarily on mentees. In this study, we investigate mentor learning and growth. We are currently lead undergraduate mentors in STUDIO and are therefore positioned to reflect on our own and other mentors’ learning. Mentors are given the opportunity to advance their leadership and mentoring skills by documenting occurrences in program time, writing weekly reflections, creating and leading curricula, and participating in weekly seminars to share experiences and address issues important to increasing diversity in STEM. In this study, documentations, reflections, and interviews are analyzed to identify shared themes and unique personal stories that illuminate mentor learning, commitment, and collaboration in the STUDIO learning environment. In early thematic analyses, we have identified several emergent themes such as the powerful role of collaborating, relationship building, and mentors’ development through leadership that support their overall academic and personal connection with STEM. As students of color remain underrepresented in the STEM field, mentors empower youth to develop their identification with STEM, despite challenges they face due to persistent stereotypes and limited resources. This research will help us better understand mentor growth and learning so that we can continue to strengthen the STUDIO mentoring team.

Mutator phenotypes due to mutations in genes encoding DNA polymerases or mismatch repair proteins lead to increased error rates during DNA replication that accelerate the evolution of cancer cells. Work in the yeast Saccharomyces cerevisae indicates that excessive DNA replication errors lead to error-induced extinction (EEX), where every cell within the population dies due to the random loss of essential functions. One escape route from this lethality is the acquisition of antimutator alleles that lower the overall mutation rate. A possible direction for cancer therapy, then, may be to exploit these antimutators in order to modulate the mutation rate of mutator cells with drugs – either to increase mutation rates to a lethal level or suppress mutation rates to the baseline level of non-cancerous cells, thus slowing the rate of tumor evolution. Our lab has identified several different antimutator mutations in genes that regulate the production of dNTPs, the building blocks of DNA. Examination of cancer genomes from mutator tumors reveal numerous candidate antimutator mutations in the corresponding human genes. We reverse-engineered these candidates into mutator yeast strains to test whether they indeed confer an antimutator phenotype. Evidence that mutations exist in mutator driven tumors that confer an antimutator phenotype would suggest that the unrestrained mutator phenotypes may be lethal to cancer cells. These findings raise the possibility of new methods of human cancer therapy by which specific genes can be targeted to manipulate mutation rates.

Elevated mutation rates due to mutations in the POLE gene, encoding DNA polymerase (Pol) Epsilon, drive a subset of colorectal carcinoma and endometrial cancers, and may accelerate tumor malignancy and pharmacological resistance in other cancers. Work with Saccharomyces cerevisiae revealed that classic mutator alleles encoding defects to Pol Epsilon proofreading mutators rely on the S-phase checkpoint, which regulates dNTP (deoxyribonucleotide triphosphates) levels by controlling the expression and activity of ribonucleotide reductase (RNR). This raises the question, do human POLE cancer alleles share this dependency on the S-phase checkpoint? And if so, do they activate the S-Phase checkpoint by creating replication stress? To investigate these questions, we created mutator yeast strains that mimic human POLE cancer alleles and deleted the S-Phase checkpoint kinase gene, DUN1, which works by indirectly controlling the expression of RNR, and thus dNTP production. Here we show that there is a consistent suppression of mutation rates in diploid strains lacking DUN1 compared to those with one or two working copies. We further extended these studies by monitoring key indicators of checkpoint signaling and replication stress. Our work suggests that targeting dNTPs in order to modulate the mutator phenotype represents a potential therapy for POLE mutator driven tumors.

Cancer, the leading cause of death worldwide, results from a combination of mutagenesis and selection for malignant phenotypes. Mutations from DNA replication errors may initiate as many as two thirds of all human cancers. Accurate DNA replication requires proofreading domains found on the major DNA polymerases as well as mismatch repair (MMR) proteins that detect and repair replication errors after DNA synthesis. Cancer-causing defects in proofreading and/or MMR lead to “mutator phenotypes”, marked by elevated mutation rates and increased cellular mutation burden. Such mutator cells occur spontaneously and drive evolution by generating mutations that enhance population survival. However, mutator cells also accumulate detrimental mutations that compromise fitness. Combined defects in polymerase proofreading and MMR cause error-induced extinction (EEX), which imposes a strong selection for cells with “antimutator” mutations that suppress the mutator phenotype. Using yeast (Saccharomyces cerevisiae), we isolated mutants that survived EEX and mapped the underlying determinants to candidate mutations (APC1, MCM5, PMS1). We are engineering these mutations into yeast strains to test whether they confer an antimutator phenotype. Understanding how mutator cells suppress elevated mutation rates will give us insights into how cancer cells survive and thrive in the face of strong mutagenesis and may suggest novel therapeutic strategies to combat this disease.

Mutator phenotypes due to mutations in genes encoding DNA polymerases or mismatch repair proteins lead to increased error rates during DNA replication that accelerate the evolution of cancer cells and contribute to chemotherapy resistance. Work in the yeast Saccharomyces cerevisiae indicates that excessive DNA replication errors can lead to error-induced extinction (EEX), where every cell within the population dies due to a random lethal mutation. Thus, a possible direction for cancer therapy may be to target antimutators, which can modulate mutation rates of mutator cells and suppress mutation rates, in order to slow the rate of tumor evolution. In a screen isolating antimutators, we identified an EEX mutation in Chromosome Transmission Fidelity 18 (ctf18-K666fs). Ctf18 directly associates with the N-terminus of DNA Polε, including part of the proofreading domain, and thus may influence mutation rates by directly affecting Polε function — a novel finding that would expand our understanding of mutator polymerases. In the current study, I determined whether Ctf18 exerts its antimutator phenotype independent of the S phase checkpoint pathway, the pathway by which all other previously isolated antimutators, such as Dun1, are known to modulate mutation rates. To accomplish this, I compared the mutation rates of double mutant strains, dun1Δ ctf18-K666fs and dun1Δ ctf18Δ, to their respective single mutants in pol2-L439V cells, where lower mutation rates would indicate additive antimutator effects from independent pathways. I also observed the degree of activation of this pathway by fluorescently tagging Sml1, a protein downstream of Dun1 in the S phase checkpoint, expecting to see decreased expression of Sml1 in cells in which the S phase checkpoint was activated. Expanding our understanding of mechanisms by which antimutators can modulate mutation rates may contribute to novel approaches for cancer treatments by targeting the mutator phenotype.

This research explores the questions: How is identity shaped by our built environment? Can storytelling along with physical movement alleviate place attachment? This research also seeks to preserve the historic identity of Seattle's central district neighborhood through the memories of its residents. It is my hope that by understanding the relationship between the built environment and human consciousness, I will learn how to design spaces that nourish the human soul while honoring it physical history. To examine these questions, I conducted an extensive literature review on theories about place and identity, and the human experience of place. I also published an online survey and conducted ten oral interviews of central district residents. A composite walking tour was then created from the physical places in their stories to highlight the overlap in their experiences, values, and identities. Through storytelling, archival research, observation, field research, map making and physical movement in these spaces, I have demonstrated a connection between memory, history, and place. My final product, a narrated walking tour, serves as a mechanism to bring people together, to educate the public about the central district and to highlight the interplay between spatial geography and social identity. The tour conjures lost places and memories into the physical world and diminishes feelings of place attachment. The tour also serves as an urban planning tool to heal displaced communities. As Seattle continues to grow and change, experiences such as this walking tour provide a living, breathing example of our shared history to anchor old residents while inspiring new citizens to honor our natural and built environment.

Non-coding regions account for approximately 98% of the genome and play a significant role in regulating and maintaining levels of gene expression via transcriptional and translational control mechanisms. Our lab focuses on the functional characterization of non-coding regulatory regions in the human retina and identifying mutations within these elements that contribute to inherited retinal diseases. In pursuit of this long-term goal, my aim is to establish an in vitro model to dissect non-coding regulatory elements in the human retina. Retinal organoid cultures are a promising new system for studying the development of the human eye, however it is currently unknown if organoids recapitulate all of the features of the adult human retina. Based on similarities of cell types and gene expression, we hypothesized that retinal organoids recapitulate some non-coding regulatory features of the normal human retina. To identify both shared and specific non-coding regulatory elements, I profiled the epigenetic landscape of developing human retinal organoids using a genome-wide method for assessing chromatin accessibility (ATAC-Seq). Chromatin accessibility is a feature of non-coding regulatory elements which ATAC-Seq revealed in human retinal organoids. I then used bioinformatic techniques to compare my organoid dataset to previous data we generated from the adult human retina and published data from the developing human retina. We found distinct sets of non-coding regulatory elements that were shared between retinal organoids and the human retina, as well as elements that were unique to each system. These comparative data will equip us with additional insight on which non-coding elements may influence retinal disease phenotypes. Furthermore, these data will potentially give us a clearer understanding of the epigenetic landscape of the developing and adult retina in a context that may drive progress towards regenerating damaged photoreceptor cells in the future.