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Updated: Sep 4, 2026
Contextual and Cued Fear Conditioning Test Using a Video Analyzing System in Mice
Published on: March 1, 2014
Impaired conditioned fear and enhanced long-term potentiation in Fmr2 knock-out mice
Yanghong Gu1, Kellie L McIlwain, Edwin J Weeber
1Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.
Abstract:
FRAXE mental retardation results from expansion and methylation of a CCG trinucleotide repeat located in exon 1 of the X-linked FMR2 gene, which results in transcriptional silencing. The product of FMR2 is a member of a family of proteins rich in serine and proline, members of which have been associated with transcriptional activation. We have developed a murine Fmr2 gene knock-out model by replacing a fragment containing parts of exon 1 and intron 1 with the Escherichia coli lacZ gene, placing lacZ under control of the Fmr2 promoter. Expression of lacZ in the knock-out animals indicates that Fmr2 is expressed in several tissues, including brain, bone, cartilage, hair follicles, lung, tongue, tendons, salivary glands, and major blood vessels. In the CNS, Fmr2 expression begins at the time that cells in the neuroepithelium differentiate into neuroblasts. Mice lacking Fmr2 showed a delay-dependent conditioned fear impairment. Long-term potentiation (LTP) was found to be enhanced in hippocampal slices of Fmr2 knock-out compared with wild-type littermates. To our knowledge, this mouse knock-out is the first example of an animal model of human mental retardation with impaired learning and memory performance and increased LTP. Thus, although a number of studies have suggested that diminished LTP is associated with memory impairment, our data suggest that increased LTP may be a mechanism that leads to impaired cognitive processing as well.
Insights
FRAXE mental retardation is caused by FMR2 gene silencing. A mouse model lacking Fmr2 shows impaired fear learning and enhanced long-term potentiation (LTP), suggesting increased LTP may impair cognitive processing.
Area of Science:
- Neuroscience
- Genetics
- Developmental Biology
Background:
- FRAXE mental retardation stems from FMR2 gene silencing due to CCG repeat expansion.
- The FMR2 gene product is a serine/proline-rich protein potentially involved in transcriptional activation.
- Understanding FMR2's function is crucial for addressing FRAXE-related cognitive deficits.
Purpose of the Study:
- To create and characterize a mouse model of FMR2 deficiency.
- To investigate the role of Fmr2 in learning, memory, and synaptic plasticity.
- To explore the relationship between FMR2, LTP, and cognitive function.
Main Methods:
- Generation of a murine Fmr2 knock-out model using gene replacement with lacZ.
- Analysis of lacZ expression to determine Fmr2 tissue distribution and developmental timing.
- Behavioral testing (conditioned fear) and electrophysiological recordings (LTP) in knock-out mice.
Main Results:
- Fmr2 expression is detected in various tissues, including the central nervous system during neurogenesis.
- Fmr2 knock-out mice exhibit impaired delay-dependent conditioned fear.
- Hippocampal long-term potentiation (LTP) is significantly enhanced in Fmr2 knock-out mice compared to wild-type.
Conclusions:
- This study presents the first animal model of FRAXE mental retardation with impaired learning and memory.
- The findings suggest that enhanced LTP, not diminished LTP, may underlie cognitive processing deficits in Fmr2 deficiency.
- This challenges existing paradigms linking LTP solely to memory enhancement and opens new avenues for understanding cognitive disorders.
