Award Date
12-1-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Life Sciences
First Committee Member
Allyson Hindle
Second Committee Member
Brandon Briggs
Third Committee Member
Laurel Raftery
Fourth Committee Member
Brian Hedlund
Fifth Committee Member
Ernesto Abel-Santos
Number of Pages
216
Abstract
Mammals are exposed to a suite of physiological challenges based on the environment in which they inhabit. Animal individuals can overcome challenges associated with the dynamic nature of their habitat through variation in phenotypic traits. The plasticity of a phenotype relies on an individual’s genome and the transcription factors that act on regulatory elements. Species living in Antarctica display physiological specializations to withstand harsh conditions, such as severe cold temperatures, shifts in available ice habitat, and annual fluctuations in daylight. To explore the connections between an individual’s genome and its phenotype, we investigated two physiologies of the Antarctic Weddell seal (Leptonychotes weddellii), diving and reproduction. We integrated multiple cellular and bioinformatic tools to investigate Weddell seal physiology based on the newly published genome.
Among phocids (true seals), Weddell seals are some of the deepest, longest divers with the ability to dive over 900 meters deep and spend over 90 minutes underwater. This behavior is supported by extensive breath-hold capacities that are facilitated by mechanisms such as 1) near-complete depletion of venous blood oxygen supplies and 2) compression of the lung under high pressures to limit barotrauma risks. These physiological features indicate that diving seals are routinely exposed to hypoxemia and atelectasis. These are considered pathologies in humans, both with sequelae mediated through stimulation of the innate immune system, directed by inflammatory cytokines. One hypothesis for how seals sustain repeated diving without development of chronic injuries is the seal’s ability to dampen their inflammation response. We investigated two components in Weddell seal blood that protect against inflammation. Chapter 2 characterized serum protein components and investigated whether protection is inherent in Weddell seals from birth or developed subsequent to diving behavior. We used an in vitro mouse macrophage model to test whether seal serum is protective against inflammatory stimulant lipopolysaccharide (LPS) and measured pro-inflammatory cytokine production following 6-h exposures. We correlated these measurements to diving behavior in 2 ways: 1) comparing inflammatory responses between experienced diving adults to novice diving pups (~35 days post-partum) and 2) correlating dive response across species with varying dive behaviors. Adult seal serum blunted the inflammatory response in mouse macrophages to a greater degree than their pup counterparts, and serum from Weddell seals is the most protective across all species examined. Additionally, proteomic analysis between pup and adult serum revealed differences including the abundance of colony stimulating factor 2 receptor beta (CSF2RB), which was 23-fold higher in adults than in pups.
Serum is only one component in blood, so we additional tested the inflammatory response in Weddell seal white blood cells. White blood cells have nuclear machinery and can mount a transcriptional response to a stimulus. When a tissue is inflamed, macrophages are among the first white blood cell that is recruited and will function to both rid the area of damage and initiate repair signaling. For chapter 3, we investigated the transcriptional difference between Weddell seal and human macrophage responses to LPS-induced inflammation. Weddell seal diving evokes hypoxemia (drop in blood oxygen levels), which in turn induces inflammation. This chapter had two main findings: 1) Weddell seal macrophages respond less to inflammatory stimuli compared to human cells, as evidenced by both a reduction in total number of differentially expressed genes (DEGs) and by a smaller fold change; and 2) Weddell seals activate unique DEGs reflecting enrichment of biological pathways that are distinct from human cells. We additionally analyzed the response of Weddell seal, human and Northern elephant seals (Mirounga angustirostris) macrophages to a dual LPS and hypoxia (1% oxygen) exposure. We found that Weddell seal macrophages have less mRNA expression for pro-inflammatory cytokines (Il6 and Tnf-) following dual exposure compared to the other species. Furthermore, Weddell seal macrophages have the highest mRNA expression of anti-inflammatory cytokines (Il1r and Tgf-) following dual exposure compared to the other species.
As the southernmost breeding mammal in the world, the reproductive physiology of Weddell seals is also worthy of investigation. The Erebus Bay population of Weddell seals is one of the most extensively studied free-ranging populations of large mammals and is part of an ongoing 50-year mark recapture study tracking demographic shifts in the population. Prior work identified a range of reproductive rates in the population of adult females, considered to have either a reproductively high output (average fecundity is higher than the population average) or reproductively low output. Chapter 4, outlines a pipeline to analyze genomic variants across 45 individuals representing high-, average-, and low-output females. We ran targeted analysis of 29 genes grouped in biological pathways associated with pregnancy, blastocyst invasion/implantation, inflammation, and cortisol. We ran a linear regression to determine if genetic variation among our sample’s genotype is correlated with reproductive output (standard deviation determined based on an individual’s total pup output from the average output). Across the 29 genes tested, we identified 222 variants (p-value < 0.05) that could be explained by the reproductive output. Among the genes, ESR1, which encodes for estrogen receptor 1, was the gene with the most variance among loci primarily associated with low-output females. While we were able to identify statistical significance, multiple considerations were discussed related to future directions.
This dissertation links genetic traits to multiple aspects of phenotype and physiology in Weddell seals. In comparative physiology, understanding how mammals can thrive in extreme environments can be a proxy to understand the boundaries of human health. Uncovering unique genes and regulatory processes that underlie physiological phenotypes can be a tool for developing targeted therapies in human medicine.
Keywords
Comparative Physiology; Innate Immunity; Reproductive Genomics
Disciplines
Biology | Medical Physiology | Physiology
File Format
File Size
16500 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Klink, Amy Christine, "Physiology and Genomics at the Bottom of the World: Genome to Phenome" (2024). UNLV Theses, Dissertations, Professional Papers, and Capstones. 5183.
http://dx.doi.org/10.34917/38330395
Rights
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