Publications by authors named "E J Hixon"

17 Publications

Neural Crest Transplantation Reveals Key Roles in the Evolution of Cavefish Development.

Integr Comp Biol 2018 09;58(3):411-420

Department of Biology, University of Maryland, College Park, MD 20742, USA.

Evolutionary changes in Astyanax mexicanus cavefish with respect to conspecific surface fish, including the regression of eyes, loss of pigmentation, and modification of the cranial skeleton, involve derivatives of the neural crest. However, the role of neural crest cells in cavefish evolution and development is poorly understood. One of the reasons is that experimental methods for neural crest analysis are not well developed in the Astyanax system. Here we describe neural crest transplantation between Astyanax surface fish and cavefish embryos. We found differences in the migration of cranial neural crest cells transplanted from the surface fish anterior hindbrain to the same region of surface fish or cavefish hosts. Cranial neural crest cells migrated extensively throughout the head, and to a lesser extent the trunk, in surface fish hosts but their migration was mostly restricted to the anterior and dorsal head regions in cavefish hosts. Cranial neural crest cells derived from the surface fish transplants invaded the degenerating eyes of cavefish hosts, resulting in increased eye size and suggesting that cavefish neural crest cells are defective in forming optic derivatives. We found that melanophores were formed in albino cavefish from grafts of surface fish trunk neural crest cells, showing that the cavefish tissue environment is conducive for pigment cell development, and implicating intrinsic changes in cavefish neural crest cells in loss of body pigmentation. It is concluded that changes in neural crest cells play key roles in the evolution of cavefish development.
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http://dx.doi.org/10.1093/icb/icy006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6145416PMC
September 2018

Design and performance evaluation of a broadband three dimensional acoustic intensity measuring system.

J Acoust Soc Am 2010 Apr;127(4):2338-46

Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712, USA.

A seven-microphone three dimensional (3D) intensity measuring system has been developed and evaluated for performance for a broad frequency band (200 Hz-6.5 kHz). Six microphones are arranged in a concentric array with one microphone at the center of the probe. The screw adjustable center microphone is the probe reference microphone, and is used for calibrations of the other microphones in the probe. This probe addresses limitations of the traditional two-microphone system in measuring acoustical properties in a 3D space from the one dimensional measurements. This probe also eliminates the need of spacers used in the existing 3D probes for broadband measurements. Diffraction and reflection effects on calibrations due to presence of the microphones and the probe supporting structure are negligible. This seven-microphone probe provided better results in the intensity measurements for the wide frequency band than that of a similar four-microphone array probe.
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http://dx.doi.org/10.1121/1.3327508DOI Listing
April 2010

Evolution of pigment cell regression in the cavefish Astyanax: a late step in melanogenesis.

Evol Dev 2004 Jul-Aug;6(4):209-18

Division of Biology, 139-74, California Institute of Technology, Pasadena, CA 91125, USA.

Pigmentation and eyes are often lost in cave-adapted animals. Although the mechanisms of eye degeneration are beginning to be understood, little is known about the evolutionary and developmental processes involved in pigment cell regression. In teleost embryos, a population of neural crest cells migrates into the body wall and differentiates into melanophores, xanthophores, and iridophores. All three pigment cell types are present in the eyed surface-dwelling form (surface fish) of the teleost Astyanax mexicanus. However, melanophores are absent or substantially reduced in number in various derived populations of the conspecific blind cave-dwelling form (cavefish). We show here that tyrosinase-positive melanoblasts are present in cavefish. DiI labeling revealed a population of trunk neural crest cells in cavefish embryos that migrate to locations normally occupied by differentiated melanophores. We also discovered a cell population in cavefish embryos and adults resembling melanoblasts in several features, including the ability to synthesize melanin when supplied with the tyrosinase substrate l-dopa. DiI-tyrosinase double-labeling and neural keel explant experiments showed that the tyrosinase-positive cells are derived from the neural crest. The number of melanoblasts varies in different adult cavefish populations relative to the extent of melanophore reduction. Although cavefish melanoblasts can synthesize melanin from exogenous l-dopa, they are unable to convert exogenous l-tyrosine to l-dopa and melanin. We conclude that pigment cell regression in cavefish is mediated by an evolutionary change late in melanogenesis that may involve an impediment in the ability to convert l-tyrosine to l-dopa and melanin.
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http://dx.doi.org/10.1111/j.1525-142X.2004.04026.xDOI Listing
March 2005

A future for dentistry in New Zealand.

Authors:
E H Hixon

N Z Dent J 1973 Jan;69(315):5-17

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January 1973
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