Abstract
To facilitate precise and convenient control of biological sample temperature, we developed a low-cost device that can be used independently or with any stereomicroscope. The purpose of the device is to control the thermal environment during experimental intervals in which a specimen must be manipulated outside of an incubator, e.g. for dissection or slide-mounting in preparation for imaging. Sample temperatures can be both cooled to below and heated to above room temperatures, and stably maintained at a precision of +/- 0.1˚C. To demonstrate the utility of this device, we report improved characterization of the penetrance of a short-acting temperature-sensitive allele in C. elegans embryos, and identification of the upper temperature threshold for embryonic viability for six Caenorhabditis species. By controlling the temperature environment even as a specimen is manipulated, this device offers consistency and flexibility, reduces environmental noise, and enables precision timing in experiments requiring temperature shifts.
Highlights
The function of living systems depends intimately on temperature
The core device is comprised of a thermoelectric cooler (TEC), which uses electrical energy to transfer heat from one side to the other; a solid copper heatsink affixed to one side of the TEC, which provides a working surface with even heat distribution to the specimen; a fan-controlled CPU heatsink affixed to the other side of the TEC, which dissipates heat; a thermistor, which reads temperature from the specimen or the working surface of the device; and a microcontroller board and two additional shields, which control the electrical draw required by the TEC to maintain the desired temperature (Fig 1)
Temperature sensitive alleles were foundational tools in the elucidation of the genetic pathways that govern the first cell divisions of the C. elegans embryo, a primary model for understanding cell polarity in animals, but the difficulty of generating and identifying conditional mutations has limited the pool of available alleles in this system [8, 16, 17]
Summary
The function of living systems depends intimately on temperature. The development of virtually all poikilotherms is sensitive to temperature, even for wild type animals in a normal thermal range [1]. Developmental timing in particular is highly responsive to temperature [2, 3]; the fruit fly Drosophila melanogaster and the nematode worm Caenorhabditis elegans develop twice as fast at 25 ̊C compared to 18 ̊C and 16 ̊C, respectively [4, 5], and the rate of nematode embryonic cell divisions increases exponentially with temperature [6]. Investigative research often depends on temperature manipulation as part of the experimental process, for example the induction of heat shock or the use of temperaturesensitive mutant alleles. Experiments involving living samples will be optimized by precise control of the thermal environment.
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