Fragile X Syndrome Patient-Derived Neurons Developing in the Mouse Brain Show FMR1-Dependent Phenotypes

Area of Science:

• Neuroscience
• Stem Cell Biology
• Genetics

Background:

• Fragile X syndrome (FXS) presents with intellectual disability, autistic behaviors, and seizures, linked to poorly understood abnormal neuronal development.
• Existing FXS models, including animal and in vitro systems, have limitations in fully recapitulating human neuronal morphology and function.
• Scarcity of patient data and therapeutic failures highlight the need for improved FXS research models.

Purpose of the Study:

• To develop a more accurate in vivo model for studying human neuronal development in Fragile X syndrome.
• To investigate the cellular and molecular changes in FXS neurons within a physiologically relevant environment.
• To gain insights into the mechanisms underlying altered neuronal development in FXS.

Main Methods:

• Coinjection of patient-derived induced pluripotent stem cell (iPSC)-neural precursor cells and isogenic control iPSC-neural precursor cells into neonatal mouse brains.
• Utilizing immune-deprived mice to allow for successful engraftment and survival of human cells.
• Employing immunofluorescence and RNA sequencing (single and bulk) to analyze cell differentiation and gene expression.

Main Results:

• Transplanted cells successfully integrated and differentiated into neurons and glial cells within the mouse brain.
• Fragile X syndrome neurons exhibited accelerated maturation following an initial developmental delay.
• Increased expression of Arc and Egr-1, along with wider dendritic protrusions, was observed in mature FXS neurons.

Conclusions:

• This in vivo transplantation model offers a unique platform for studying human neuronal development in FXS.
• The findings provide novel insights into the specific alterations in neuronal maturation and morphology characteristic of FXS.
• The 3D physiological context of the brain facilitates a better understanding of FXS pathophysiology.