Limits...
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

Neurogenesis is sensitive to FMRP levels. Summary diagram showing the consequences of perturbing FMRP levels on the labeled cell population. The numbers and proportions of neural progenitor cells (purple) and neurons (green), as well as the dendritic arbor morphology of neurons are altered in the presence of fmr1a MO or overexpression of FMRP. LOW fmr1a MO increases NPC apoptosis, leading to a reduction in the progenitor pool and a lower total number of cells present at 3 dfe compared to control. The neurons generated with LOW fmr1a MO have a trend toward deficient dendritic arbor development. HIGH fmr1a MO increases apoptosis compared to LOW fmr1a MO. In addition, HIGH fmr1a MO decreases proliferation and increases NPC differentiation into neurons. This leads to a greater reduction of the progenitor pool, a lower total number of cells present at 3 dfe, and a larger proportion of neurons among the cell population at 3 dfe. In addition, those neurons have a persistent defect in dendrite arbor elaboration. LOW FMRP overexpression does not result in defects in cell proliferation, cell death, differentiation, or dendritic morphology. HIGH FMRP overexpression increases cell death, decreases proliferation, and increases differentiation leading to a complete loss of the progenitor pool at 3 dfe. Neuron numbers are at control levels at 3 dfe because of the dramatic increase in differentiation, but those neurons have a defect in dendritic arbor development.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4384423&req=5

Figure 8: Neurogenesis is sensitive to FMRP levels. Summary diagram showing the consequences of perturbing FMRP levels on the labeled cell population. The numbers and proportions of neural progenitor cells (purple) and neurons (green), as well as the dendritic arbor morphology of neurons are altered in the presence of fmr1a MO or overexpression of FMRP. LOW fmr1a MO increases NPC apoptosis, leading to a reduction in the progenitor pool and a lower total number of cells present at 3 dfe compared to control. The neurons generated with LOW fmr1a MO have a trend toward deficient dendritic arbor development. HIGH fmr1a MO increases apoptosis compared to LOW fmr1a MO. In addition, HIGH fmr1a MO decreases proliferation and increases NPC differentiation into neurons. This leads to a greater reduction of the progenitor pool, a lower total number of cells present at 3 dfe, and a larger proportion of neurons among the cell population at 3 dfe. In addition, those neurons have a persistent defect in dendrite arbor elaboration. LOW FMRP overexpression does not result in defects in cell proliferation, cell death, differentiation, or dendritic morphology. HIGH FMRP overexpression increases cell death, decreases proliferation, and increases differentiation leading to a complete loss of the progenitor pool at 3 dfe. Neuron numbers are at control levels at 3 dfe because of the dramatic increase in differentiation, but those neurons have a defect in dendritic arbor development.

Mentions: Our in vivo time-lapse imaging approach followed a GFP-labeled population of Sox2-expressing NPCs and their progeny over 3 d to evaluate several distinct cellular events contributing to neurogenesis, including NPC proliferation and survival, the rate of differentiation of progenitors into neurons, and dendritic arbor elaboration in neurons. Over 3 d, the number of eGFP-labeled cells in control animals increases as labeled NPCs proliferate. In addition, the proportion of NPCs decrease and the proportion of neurons increase within the labeled population as neurons differentiate. Finally, as neurons mature, their dendritic arbors become more elaborate. The level of FMRP is critical to each of these processes during neurogenesis and the degree to which FMRP is knocked down or overexpressed changes the phenotypic outcome (Fig. 8). For example, with respect to FMRP knockdown, LOW fmr1a MO does not affect NPC proliferation, but increases NPC cell death compared to CMO. The proportions of NPCs and neurons within the labeled population do not change, suggesting that differentiation is normal; however, the neurons tend to have deficient dendritic arbor development. A greater degree of FMRP knockdown with HIGH fmr1a MO produces a trend toward more cell death than seen with LOW fmr1a MO. In addition, NPC proliferation decreases and neuronal differentiation increases. Together, this results in a smaller cell population but a higher proportion of neurons. Furthermore, the resulting neurons have a more severe and lasting deficit in dendritic arbor growth and branching than seen with lower FMRP knockdown. These data indicate that higher levels of FMRP knockdown affect some of the cellular events contributing to neurogenesis, such as NPC proliferation and neuronal differentiation, whereas lower levels of knockdown affect other cellular events, such as NPC apoptosis, suggesting that these processes are differentially sensitive to different levels of FMRP.


FMRP regulates neurogenesis in vivo in Xenopus laevis tadpoles.

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

Neurogenesis is sensitive to FMRP levels. Summary diagram showing the consequences of perturbing FMRP levels on the labeled cell population. The numbers and proportions of neural progenitor cells (purple) and neurons (green), as well as the dendritic arbor morphology of neurons are altered in the presence of fmr1a MO or overexpression of FMRP. LOW fmr1a MO increases NPC apoptosis, leading to a reduction in the progenitor pool and a lower total number of cells present at 3 dfe compared to control. The neurons generated with LOW fmr1a MO have a trend toward deficient dendritic arbor development. HIGH fmr1a MO increases apoptosis compared to LOW fmr1a MO. In addition, HIGH fmr1a MO decreases proliferation and increases NPC differentiation into neurons. This leads to a greater reduction of the progenitor pool, a lower total number of cells present at 3 dfe, and a larger proportion of neurons among the cell population at 3 dfe. In addition, those neurons have a persistent defect in dendrite arbor elaboration. LOW FMRP overexpression does not result in defects in cell proliferation, cell death, differentiation, or dendritic morphology. HIGH FMRP overexpression increases cell death, decreases proliferation, and increases differentiation leading to a complete loss of the progenitor pool at 3 dfe. Neuron numbers are at control levels at 3 dfe because of the dramatic increase in differentiation, but those neurons have a defect in dendritic arbor development.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: Neurogenesis is sensitive to FMRP levels. Summary diagram showing the consequences of perturbing FMRP levels on the labeled cell population. The numbers and proportions of neural progenitor cells (purple) and neurons (green), as well as the dendritic arbor morphology of neurons are altered in the presence of fmr1a MO or overexpression of FMRP. LOW fmr1a MO increases NPC apoptosis, leading to a reduction in the progenitor pool and a lower total number of cells present at 3 dfe compared to control. The neurons generated with LOW fmr1a MO have a trend toward deficient dendritic arbor development. HIGH fmr1a MO increases apoptosis compared to LOW fmr1a MO. In addition, HIGH fmr1a MO decreases proliferation and increases NPC differentiation into neurons. This leads to a greater reduction of the progenitor pool, a lower total number of cells present at 3 dfe, and a larger proportion of neurons among the cell population at 3 dfe. In addition, those neurons have a persistent defect in dendrite arbor elaboration. LOW FMRP overexpression does not result in defects in cell proliferation, cell death, differentiation, or dendritic morphology. HIGH FMRP overexpression increases cell death, decreases proliferation, and increases differentiation leading to a complete loss of the progenitor pool at 3 dfe. Neuron numbers are at control levels at 3 dfe because of the dramatic increase in differentiation, but those neurons have a defect in dendritic arbor development.
Mentions: Our in vivo time-lapse imaging approach followed a GFP-labeled population of Sox2-expressing NPCs and their progeny over 3 d to evaluate several distinct cellular events contributing to neurogenesis, including NPC proliferation and survival, the rate of differentiation of progenitors into neurons, and dendritic arbor elaboration in neurons. Over 3 d, the number of eGFP-labeled cells in control animals increases as labeled NPCs proliferate. In addition, the proportion of NPCs decrease and the proportion of neurons increase within the labeled population as neurons differentiate. Finally, as neurons mature, their dendritic arbors become more elaborate. The level of FMRP is critical to each of these processes during neurogenesis and the degree to which FMRP is knocked down or overexpressed changes the phenotypic outcome (Fig. 8). For example, with respect to FMRP knockdown, LOW fmr1a MO does not affect NPC proliferation, but increases NPC cell death compared to CMO. The proportions of NPCs and neurons within the labeled population do not change, suggesting that differentiation is normal; however, the neurons tend to have deficient dendritic arbor development. A greater degree of FMRP knockdown with HIGH fmr1a MO produces a trend toward more cell death than seen with LOW fmr1a MO. In addition, NPC proliferation decreases and neuronal differentiation increases. Together, this results in a smaller cell population but a higher proportion of neurons. Furthermore, the resulting neurons have a more severe and lasting deficit in dendritic arbor growth and branching than seen with lower FMRP knockdown. These data indicate that higher levels of FMRP knockdown affect some of the cellular events contributing to neurogenesis, such as NPC proliferation and neuronal differentiation, whereas lower levels of knockdown affect other cellular events, such as NPC apoptosis, suggesting that these processes are differentially sensitive to different levels of FMRP.

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