Tbr1 Misexpression Alters Neuronal Development in the Cerebral Cortex.

Area of Science:

• Neuroscience
• Developmental Biology
• Genetics

Background:

• Transcription factor (TF) expression changes are vital for brain development and linked to neurodevelopmental disorders.
• T-box brain1 (Tbr1) is essential for neocortical layer VI formation; its mutations are associated with human cerebral cortex malformations and autism spectrum disorder (ASD).
• Increased Tbr1 levels are implicated in ASD-like symptoms, but their developmental effects are understudied.

Purpose of the Study:

• To investigate the impact of Tbr1 misexpression on mouse neural progenitor cells (NPCs) during critical neocortical development stages.
• To understand how altered Tbr1 levels affect neuronal migration, specification, and morphology.
• To explore the potential link between Tbr1 misexpression and cortical brain malformations.

Main Methods:

• Analysis of Tbr1 misexpression in mouse NPCs at embryonic day 14.5 (E14.5).
• Assessment of cell distribution in cortical layers at embryonic day 18.5 (E18.5) and postnatal day 7 (P7).
• Evaluation of neuronal marker expression (Sox5, Cux1), cell morphology, dendrite development, and corpus callosum formation.

Main Results:

• Tbr1 misexpression led to cell accumulation in intermediate and deep cortical layers, with reduced numbers in upper layers by E18.5.
• Increased Sox5+ cells in deep layers and decreased Cux1+ cells in upper layers were observed.
• Abnormal neuronal migration, altered multipolar-bipolar neuron morphology, reduced dendrite growth, and disrupted corpus callosum formation were identified.

Conclusions:

• Tbr1 misexpression in cortical NPCs delays or disrupts neuronal migration, specification, and dendrite development.
• The study highlights Tbr1's critical role in normal cortical development and corpus callosum formation.
• Ectopic Tbr1 upregulation during development may contribute to cortical brain malformations and neurodevelopmental disorders.