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Altered mossy fiber distributions in adult Fmr1 (FVB) knockout mice
Tammy L Ivanco1, William T Greenough
1Beckman Institute, University of Illinois, Urbana 61801, USA. ivancotl@ms.umanitoba.ca
Abstract:
The fragile-X mental retardation protein (FMRP) is greatly reduced or absent in individuals with fragile-X mental retardation syndrome, a common, heritable form of mental retardation. Morphological studies suggest that this protein functions in normal synapse maturation and neuronal plasticity. Examination of human brain autopsy tissue has shown that fragile-X patients exhibit long, thin spines more frequently, and stubby mushroom-shaped spines less frequently, than these two types of spines are seen in normal autopsy tissue. Fragile-X tissue also has a greater density of these spines along dendrites, which suggests a possible failure of synapse elimination. Fmr1 knockout mice and wild-type littermates brains were processed for Timm staining, which reveals the zinc-rich terminals of the dentate gyrus, the mossy fibers. The Fmr1 knockout mice exhibited a pattern of Timm granule-staining within the stratum oriens of subfield CA3 and the inner molecular layer that was significantly different than staining seen in wild-type animals. The sources and consequences of the altered terminal staining are unclear, but are discussed in relation to immature synapse morphology, a failure of normal regression of synapses, and a potential biological penalty of such a failure to regress.
Insights
Fragile-X syndrome is linked to reduced fragile-X mental retardation protein (FMRP), affecting synapse development. Studies reveal abnormal spine morphology and density in fragile-X brains, suggesting impaired synapse elimination and neuronal plasticity.
Area of Science:
- Neuroscience
- Genetics
- Developmental Biology
Background:
- Fragile-X mental retardation syndrome (FXS) is a common heritable form of intellectual disability.
- Reduced or absent fragile-X mental retardation protein (FMRP) is a hallmark of FXS.
- FMRP is implicated in normal synapse maturation and neuronal plasticity.
Purpose of the Study:
- To investigate the impact of FMRP absence on synapse morphology and density in fragile-X patients.
- To compare synaptic terminal staining patterns in Fmr1 knockout mice and wild-type littermates.
Main Methods:
- Examination of human brain autopsy tissue from fragile-X patients and normal individuals.
- Timm staining of Fmr1 knockout mouse brains and wild-type littermate brains to visualize zinc-rich synaptic terminals.
Main Results:
- Fragile-X brain tissue showed increased long, thin spines and decreased stubby, mushroom-shaped spines compared to normal tissue.
- A higher density of spines along dendrites in fragile-X tissue suggests a failure in synapse elimination.
- Fmr1 knockout mice exhibited distinct Timm granule-staining patterns in specific hippocampal subfields (CA3) and the inner molecular layer compared to wild-type animals.
Conclusions:
- Altered spine morphology and density in fragile-X syndrome indicate potential failures in synapse maturation and elimination.
- Distinct Timm staining in Fmr1 knockout mice suggests abnormal synaptic terminal development or regression.
- These synaptic abnormalities may contribute to the cognitive deficits observed in fragile-X syndrome.
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