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FMRP regulates neurogenesis in vivo in Xenopus laevis tadpoles.

Faulkner RL, Wishard TJ, Thompson CK, Liu HH, Cline HT - eNeuro (2015 Jan-Feb)

Bottom Line: Recent studies suggest that loss of FMRP results in aberrant neurogenesis, but neurogenic defects have been variable.Animals with increased or decreased levels of FMRP have significantly decreased neuronal proliferation and survival.These studies show promise in using Xenopus as an experimental system to study fundamental deficits in brain development with loss of FMRP and give new insight into the pathophysiology of FXS.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Dorris Neuroscience Center, Department of Molecular and Cellular Neuroscience, The Scripps Research Institute, La Jolla, California 92037.

ABSTRACT

Fragile X Syndrome (FXS) is the leading known monogenic form of autism and the most common form of inherited intellectual disability. FXS results from silencing the FMR1 gene during embryonic development, leading to loss of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein that regulates mRNA transport, stability, and translation. FXS is commonly thought of as a disease of synaptic dysfunction, however, FMRP expression is lost early in embryonic development, well before most synaptogenesis occurs. Recent studies suggest that loss of FMRP results in aberrant neurogenesis, but neurogenic defects have been variable. We investigated whether FMRP affects neurogenesis in Xenopus laevis tadpoles which express a homolog of FMR1. We used in vivo time-lapse imaging of neural progenitor cells and their neuronal progeny to evaluate the effect of acute loss or over-expression of FMRP on neurogenesis in the developing optic tectum. We complimented the time-lapse studies with SYTOX labeling to quantify apoptosis and CldU labeling to measure cell proliferation. Animals with increased or decreased levels of FMRP have significantly decreased neuronal proliferation and survival. They also have increased neuronal differentiation, but deficient dendritic arbor elaboration. The presence and severity of these defects was highly sensitive to FMRP levels. These data demonstrate that FMRP plays an important role in neurogenesis and suggest that endogenous FMRP levels are carefully regulated. These studies show promise in using Xenopus as an experimental system to study fundamental deficits in brain development with loss of FMRP and give new insight into the pathophysiology of FXS.

No MeSH data available.


Related in: MedlinePlus

FMRP is expressed in Xenopus optic tectal progenitors and neurons. A, Schematic of the Xenopus tadpole optic tectum showing the location of neural progenitor cells (purple) and neurons (green) extending processes into the neuropil. B, A single optical confocal section of stage 47 Xenopus optic tectum shows widespread FMRP immunoreactivity. Scale bar, 100 μm. C, A higher magnification view from a single optical section in a different animal shows FMRP immunoreactivity across all cell layers and throughout the neuropil. Scale bar, 50 μm.
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Figure 1: FMRP is expressed in Xenopus optic tectal progenitors and neurons. A, Schematic of the Xenopus tadpole optic tectum showing the location of neural progenitor cells (purple) and neurons (green) extending processes into the neuropil. B, A single optical confocal section of stage 47 Xenopus optic tectum shows widespread FMRP immunoreactivity. Scale bar, 100 μm. C, A higher magnification view from a single optical section in a different animal shows FMRP immunoreactivity across all cell layers and throughout the neuropil. Scale bar, 50 μm.

Mentions: While it is known that fmr1 mRNA is expressed throughout Xenopus laevis embryonic development (Lim et al., 2005; Gessert et al., 2010), the expression pattern of FMRP in the optic tectum during visual system development is unknown. To examine expression of FMRP, we first performed Western blot of stage 47 − 48 tadpole midbrain labeled with FMRP antibody, which revealed a band at approximately 72 kD (data not shown and Fig. 3E). We found that rat brain lysate labeled with FMRP antibody had a similar band (data not shown). To elucidate a more detailed expression pattern in the optic tectum, we performed immunohistochemistry for FMRP in stage 47 tadpoles. FMRP immunolabeling was detected in neural progenitor cells (NPCs) that line the brain ventricle and neurons that are located lateral to progenitors (Fig. 1A−C). Furthermore, FMRP was expressed as punctate labeling throughout the tectal neuropil. This expression profile suggests that FMRP may regulate cell proliferation and/or differentiation of NPCs into neurons as well as aspects of neuronal development.


FMRP regulates neurogenesis in vivo in Xenopus laevis tadpoles.

Faulkner RL, Wishard TJ, Thompson CK, Liu HH, Cline HT - eNeuro (2015 Jan-Feb)

FMRP is expressed in Xenopus optic tectal progenitors and neurons. A, Schematic of the Xenopus tadpole optic tectum showing the location of neural progenitor cells (purple) and neurons (green) extending processes into the neuropil. B, A single optical confocal section of stage 47 Xenopus optic tectum shows widespread FMRP immunoreactivity. Scale bar, 100 μm. C, A higher magnification view from a single optical section in a different animal shows FMRP immunoreactivity across all cell layers and throughout the neuropil. Scale bar, 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384423&req=5

Figure 1: FMRP is expressed in Xenopus optic tectal progenitors and neurons. A, Schematic of the Xenopus tadpole optic tectum showing the location of neural progenitor cells (purple) and neurons (green) extending processes into the neuropil. B, A single optical confocal section of stage 47 Xenopus optic tectum shows widespread FMRP immunoreactivity. Scale bar, 100 μm. C, A higher magnification view from a single optical section in a different animal shows FMRP immunoreactivity across all cell layers and throughout the neuropil. Scale bar, 50 μm.
Mentions: While it is known that fmr1 mRNA is expressed throughout Xenopus laevis embryonic development (Lim et al., 2005; Gessert et al., 2010), the expression pattern of FMRP in the optic tectum during visual system development is unknown. To examine expression of FMRP, we first performed Western blot of stage 47 − 48 tadpole midbrain labeled with FMRP antibody, which revealed a band at approximately 72 kD (data not shown and Fig. 3E). We found that rat brain lysate labeled with FMRP antibody had a similar band (data not shown). To elucidate a more detailed expression pattern in the optic tectum, we performed immunohistochemistry for FMRP in stage 47 tadpoles. FMRP immunolabeling was detected in neural progenitor cells (NPCs) that line the brain ventricle and neurons that are located lateral to progenitors (Fig. 1A−C). Furthermore, FMRP was expressed as punctate labeling throughout the tectal neuropil. This expression profile suggests that FMRP may regulate cell proliferation and/or differentiation of NPCs into neurons as well as aspects of neuronal development.

Bottom Line: Recent studies suggest that loss of FMRP results in aberrant neurogenesis, but neurogenic defects have been variable.Animals with increased or decreased levels of FMRP have significantly decreased neuronal proliferation and survival.These studies show promise in using Xenopus as an experimental system to study fundamental deficits in brain development with loss of FMRP and give new insight into the pathophysiology of FXS.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Dorris Neuroscience Center, Department of Molecular and Cellular Neuroscience, The Scripps Research Institute, La Jolla, California 92037.

ABSTRACT

Fragile X Syndrome (FXS) is the leading known monogenic form of autism and the most common form of inherited intellectual disability. FXS results from silencing the FMR1 gene during embryonic development, leading to loss of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein that regulates mRNA transport, stability, and translation. FXS is commonly thought of as a disease of synaptic dysfunction, however, FMRP expression is lost early in embryonic development, well before most synaptogenesis occurs. Recent studies suggest that loss of FMRP results in aberrant neurogenesis, but neurogenic defects have been variable. We investigated whether FMRP affects neurogenesis in Xenopus laevis tadpoles which express a homolog of FMR1. We used in vivo time-lapse imaging of neural progenitor cells and their neuronal progeny to evaluate the effect of acute loss or over-expression of FMRP on neurogenesis in the developing optic tectum. We complimented the time-lapse studies with SYTOX labeling to quantify apoptosis and CldU labeling to measure cell proliferation. Animals with increased or decreased levels of FMRP have significantly decreased neuronal proliferation and survival. They also have increased neuronal differentiation, but deficient dendritic arbor elaboration. The presence and severity of these defects was highly sensitive to FMRP levels. These data demonstrate that FMRP plays an important role in neurogenesis and suggest that endogenous FMRP levels are carefully regulated. These studies show promise in using Xenopus as an experimental system to study fundamental deficits in brain development with loss of FMRP and give new insight into the pathophysiology of FXS.

No MeSH data available.


Related in: MedlinePlus