Directed positioning of nuclei in livingParamecium tetraurelia: Use of the laser optical force trap for developmental biology
✍ Scribed by Aufderheide, Karl J. ;Du, Qing ;Fry, Edward S.
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 819 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0192-253X
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✦ Synopsis
We have constructed a laser optical force trap ("laser tweezers") by coupling an Nd:YAG laser to an optical microscope with a high numerical aperture objective. The laser beam (approximately 0.1 W power) is focused to a diffraction-limited spot at the specimen plane of the objective: the wavelength chosen (1,064 nrn) is not strongly absorbed by most biological materials and is thus not ablative. Because the intensity of the laser beam increases towards the center of the focal spot, small particles brought near the spot will be attracted to the center and held there. Movement of the laser beam will tend to move any trapped particles with it. The laser tweezers can permit precise, nondestructive repositioning of small structures inside a living cell, without recourse to rnicromanipulators. Initial work has involved the use of laser tweezers on cells of Paramecium tetraurelia held by a rotocornpressor. We have been able to trap and reposition small organelles, especially the highly refractile structures known as crystals. Using a trapped crystal as a "tool," we have been able to push micronuclei and other structures for many micrometers to virtually any desired location in a cell. In spite of extended exposure of specific structures and of individual cells to the laser beam, no damage has been detectible. Exposed cells, which were removed from the rotocornpressor and cultured, showed complete viabilty. The laser tweezers technique shows tremendous potential for applications to the study of many fundamental cellular and developmental phenomena in paramecia and other ciliates. For example, we intend to use this technique to investigate temporal and spatial characteristics of nuclear determining regions during sexual reorganization in Parame- cium. 0 1992 Wiley-Llss, Inc light for optical tweezers is chosen for minimal absorption by the structures one wishes to trap so that no damage is imposed by the technique. Calculations in-