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Abstract
Background: Previous epidemiological findings have implicated hypoxia as a risk factor for craniofacial defects including cleft lip, microtia and branchial arch anomalies. This study tests the hypothesis that hypoxic exposure results in craniofacial shape variation in a zebrafish model. Methods: Three sets of zebrafish embryos were raised in uniform conditions with the exception of dissolved oxygen level. At 24 hours past fertilization (hpf) embryos were placed in hypoxic conditions (70% or 50% dissolved oxygen tank water) and compared to unexposed control embryos. After 24 hours of exposure to hypoxia, the embryos were incubated under normoxia. Larvae were collected at 5 days post fertilization (dpf) and stained for cartilage. Images were taken of each specimen and subsequently landmarked to capture viscerocranial morphology. A geometric morphometric analysis was performed to compare shape variation across groups. Results: The mean branchial arch shape of each exposure group was significantly different from controls (p<0.001). Principal components analysis revealed a clear separation of the three groups, with controls at one end of the shape spectrum, the 50% hypoxia group at the other end, and the 70% hypoxia group spanning the variation in between. Conclusions: This experiment shows that hypoxia exposure at 24hpf is capable of affecting craniofacial shape in a dose-dependent manner. These results may have implications not only for high altitude fetal health, but other environments, behaviors and genes that affect fetal oxygen delivery.
Highlights
There are multiple lines of evidence indicating that hypoxia can alter craniofacial development
The observed prevalence rate for microtia is five times greater for individuals living at high-altitude compared with those living at low altitude in the same general region, suggesting that development of the first and second branchial arches is susceptible to hypoxia [5]
Point(120 hpf) was chosen because it is within entire coordinate dataset to align all the is a similar data-reduction method, but where a developmental window where the visceral landmarks in the same coordinate system, principal components analysis (PCA) reduces the data without any assumpcartilages are well developed but just prior to which makes all specimens comparable to one tions regarding group membership, in a canonical variate analysis (CVA)
Summary
There are multiple lines of evidence indicating that hypoxia can alter craniofacial development. There is evidence that hypoxia can affect a broader range of structures comprising the craniofacial complex, including branchial-arch related morphology [2,4]. The observed prevalence rate for microtia is five times greater for individuals living at high-altitude compared with those living at low altitude in the same general region, suggesting that development of the first and second branchial arches is susceptible to hypoxia [5]. While zebrafish are most often used to explore genetic questions, they provide an opportunity to test environmental effects such as oxygen availability on phenotypic outcomes. The structures comprising the viscerocranium are derived from branchial arches. The first hypothesis contends that hypoxia will alter the shape of first and second branchial arch-derived structures in developing zebrafish embryos. This site is published by the University Library System, University of Pittsburgh as part of its D-Scribe Digital Publishing Program and is cosponsored by the University of Pittsburgh Press
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