Academic journal article The Science Teacher

Lights and Larvae: Using Optogenetics to Teach Recombinant DNA and Neurobiology

Academic journal article The Science Teacher

Lights and Larvae: Using Optogenetics to Teach Recombinant DNA and Neurobiology

Article excerpt

[ILLUSTRATION OMITTED]

Switching genes between organisms and controlling an animal's brain using lasers may seem like science fiction, but with advancements in a technique called optogenetics, such experiments are now common in neuroscience research. Optogenetics combines recombinant DNA technology with a controlled light source to help researchers address biomedical questions in the life sciences. The technique has gained the most traction in neurobiology--the biology of the nervous system--where specific wavelengths of light are used to control or measure the activity of neurons in transgenic organisms (i.e., those with artificially inserted genes).

These optical recording and stimulation techniques are used in nervous system preparations ranging from individual cells in culture to whole organisms, where the observations and data collected have been used to determine which neurons are involved in specific animal behaviors. In this article, we describe an inexpensive Drosophila (fruit fly) optogenetics experiment used to teach principles of the nervous system, genetics, and bioengineering at the high school level. (See sidebar [p. 44] for specific learning objectives and key concepts for the lab.)

Fruit flies receive an algae gene

Algae and other microorganisms have been known to sense and emit light (Foster and Smyth 1980). Advances in molecular biology techniques near the end of the 20th century enabled researchers to determine which proteins were involved in phototaxis (movement in response to light), clone the respective genes, and transfer them into new species for research. The proteins themselves are called channelrhodopsins, which are transmembrane ion channels that convey a non-specific ion flux when the channel is activated by a specific wavelength of light.

Channelrhodopsin-2 (ChR2) is sensitive to blue light. By introducing point mutations into the gene, researchers have altered the light sensitivity and optimized ion conduction in these channels, making photo-activation more efficient and easier to use. These advances paved the way for optogenetics to be implemented in teaching laboratories. The basic methods and concepts for using optogenetics in the undergraduate classroom have been developed by Pulver and colleagues (Pulver et al. 2011a; Pulver et al. 2011b; Pulver and Berni 2012). Here we have adapted those exercises to a high school--level module that addresses core disciplinary ideas in the Next Generation Science Standards (NGSS Lead States 2013) (Figure 1).

Expression of ChR2 in Drosophila melanogaster is restricted to motor neurons

A huge breakthrough in Drosophila transgenics occurred when the yeast GAL4-UAS binary expression system was introduced into the fly genome (Brand and Perrimon 1993; Duffy 2002). Thus the transgenic ChR2 could be expressed in specific subsets of cells using this standard binary expression system. The ChR2 transgene is controlled by the yeast upstream activation sequence (UAS) for a galactose-induced transcription factor (GAL4), meaning that the transgene is carried in every cell but is only expressed where GAL4 is expressed. Expression of the GAL4 gene is controlled by a promoter sequence either from a nearby promoter in the fly's genome or a specific promoter that is added with the GAL4 transgene sequence. By adding a promoter to the GAL4 sequence that is expressed specifically in the nervous system (e.g., a gene that codes for an enzyme involved in synthesis of a neurotransmitter), the GAL4 gene only gets expressed in the nervous system, thus activating expression of the ChR2 transgene specifically in the nervous system.

The promoter used to drive expression of GAL4 in the flies used for this activity is called OK371-GAL4. The promoter element is from the Drosophila vesicular glutamate transporter gene (DVGLUT) that is expressed almost exclusively in neurons that release glutamate (Mahr and Aberle 2006). …

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