| Abstract No.: | C-C3093 |
| Country: | Canada |
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| Title: | REGULATION OF A NEURONALLY EXPRESSED THY-1-YFP REPORTER TRANSGENE IN A RETT SYNDROME MOUSE MODEL |
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| Authors/Affiliations: | 1 David Stuss*; 1 Kerry Delaney;
1 University of Victoria, BC, Canada
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| Content: | Objective: Rett Syndrome (RTT) is a neurodevelopmental disorder that primarily affects young females. The majority of cases of classical RTT are caused by mutations in the X-linked gene MECP2. To facilitate morphometric studies of neurons in an RTT mouse model, we have generated a hybrid MeCP2-null mouse line that also expresses transgenic YFP (yellow fluorescent protein) driven by the Thy-1 promoter. Concurrent with stereological analysis of dendritic arborization, our aim is to characterize an apparent interaction between the Thy-1-YFP transgene and MeCP2.
Materials and methods:
Mecp2 mutant mice (Mecp2tm1.1Jae line) were crossed with the YFP-H transgenic mouse line (B6.Cg-Tg (Thy1-YFPH)2Jrs/J). The YFP-H line expresses YFP in a subset of neocortical Layer V pyramidal neurons. Cortical regions were systematically analyzed for the proportion of YFP-positive neurons in 11-week old mutant (Mecp2-/y, YFP+/-) vs. wild-type (Mecp2+/y, YFP+/- ) male littermates. MeCP2-null males are highly symptomatic at this age. To assess whether the Thy-1-YFP interaction is a promoter-dependent or promoter-independent effect, we crossed Mecp2 mutant mice with the YFP-16 line (B6.Cg-Tg (Thy1-YFP)16Jrs), in which YFP is expressed in the majority of neurons in all cortical layers. Fluorometric analysis of motor and somatosensory cortex was done in 8-week old mutant (Mecp2-/y, YFP+/-) vs. wild-type (Mecp2+/y, YFP+/-) male littermates.
Results: In the YFP-H hybrid mouse line, we observe a region-dependent reduction in the number of YFP-expressing neurons in highly symptomatic 11-week old male MeCP2-null mice compared to wild-type littermates. Significant reductions occurred in multiple cortical regions including motor, insular, somatosensory, and visual cortex. In the YFP-16 hybrid line, reduced global fluorescence is observed in both motor and somatosensory cortex in male MeCP2-null mice vs. wild-type littermates.
Conclusion: We demonstrate that two hybrid MeCP2 mutant / Thy-1-YFP transgenic mouse lines exhibit either a selective reduction in the number of fluorescent neurons (YFP-H line) or in total fluorescence of larger cortical regions (YFP-16 line). MeCP2 is a DNA-binding protein involved in transcriptional repression. These data suggest that the reduced YFP expression is not an artifact of either transgene insertion site or transgene copy number, but rather an indirect interaction between MeCP2 and the Thy-1 promoter sequence. This may present an opportunity to use the upregulation of YFP expression as a means of assaying MeCP2 gene replacement in MeCP2-null mice.
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