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1 Section of Integrative Physiology and Neurobiology, Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder 80309 - 0334; and 2 Department of Pharmaceutical Sciences, University of Colorado Health Sciences Center, Denver, Colorado 80262
Diapausing embryos of
Austrofundulus limnaeus survive desiccating conditions by
reducing evaporative water loss. Over 40% of diapause II embryos
survive 113 days of exposure to 75.5% relative humidity. An early loss
of water from the perivitelline space occurs during days
1-2, but thereafter, rates of water loss are reduced to near
zero. No dehydration of the embryonic tissue is indicated based on
microscopic observations and the retention of bulk (freezable) water in
embryos as judged by differential scanning calorimetry. Such high
resistance to desiccation is unprecedented among aquatic vertebrates.
Infrared spectroscopy indicates frequent intermolecular contacts via
-sheet (14%) in hydrated egg envelopes (chorions). These
-sheet
contacts increase to 36% on dehydration of the egg envelope.
Interestingly, the egg envelope is composed of protein fibrils with
characteristics of amyloid fibrils usually associated with human
disease. These features include a high proportion of intermolecular
-sheet, positive staining and green birefringence with Congo red,
and detection of long, unbranched fibrils with a diameter of 4-6
nm. The high resistance of diapause II embryos to water stress is not
correlated with ontogenetic changes in the egg envelope.
Austrofundulus limnaeus; diapause; chorion
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