An investigation into the genetic control of thalamocortical tract projection in the mouse using a fluorescent reporter transgene

• Main Author: Pratt, Thomas
• Published: University of Edinburgh 2001
• Subjects: 572.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660740

Studies of mutant mice whose thalamocortical tract is disrupted illustrate that genes involved in programming thalamocortical tract navigation are required by projecting cells of the dorsal thalamus and along its route to supply axon navigation cues. Small-eye homozygotes (<i>Pax6^Sey/Sey</i>) in which the transcription factor Pax6 is inactivated exhibit a range of defects throughout the developing central nervous system, including a failure in thalamocortical tract formation, and die at birth. The <i>Pax6^sey/Sey</i> phenotype describes disruption of both the dorsal thalamus and the tissues through which the thalamocortical tract navigates so does not reveal whether axons projected by the dorsal thalamus fail to navigate due to intrinsic mis-programming or due to a lack of important navigational cues along the route. To test the hypothesis that Pax6 is required within the dorsal thalamus for tract projection I developed a novel <i>in vitro</i> assay for thalamic axon navigation and cell surface properties. First I generated lines of embryonic stem (ES) cells which ubiquitously express a tau tagged green fluorescent protein (tau-GFP) transgene. Germline transmission of ES lines produced two lines of transgenic mice designated TgTP6.3 and TgTP6.4. I show that the tau-GFP transgene is ubiquitously expressed in developing TgTP6.3 brain and that tau tagging anchors tau-GFP to the microtubule component of the cytoskeleton resulting in clear fluorescent marking of subcellular structures, including axons and the mitotic machinery. The experimental potential of the TgTP6.3 mice is demonstrated in several cell mixing paradigms, including mouse chimeras and brain cell and tissue culture systems, where tau-GFP cells and axons can easily be detected against a background of unlabelled cells and tissues. The TgTP6.4 line exhibits very low levels of tau-GFP expression in the developing brain so is unsuitable for these experiments.