Assembloid model to study loop circuits of the human nervous system

Area of Science:

• Neuroscience
• Developmental Biology
• Stem Cell Biology

Background:

• Cortico-striatal-thalamic-cortical (CSTC) circuits are crucial for sensorimotor processing, with dysfunctions linked to neuropsychiatric disorders.
• Investigating human CSTC circuits in early development has been challenging due to limited direct functional access.

Purpose of the Study:

• To develop an *in vitro* human CSTC circuit model using stem cells for functional investigation.
• To explore emergent network activity and neuronal connectivity within this model.
• To study the impact of genetic variations, such as *ASH1L* gene loss, on CSTC circuit function.

Main Methods:

• Generation of regionalized neural organoids resembling CSTC components.
• Assembly of organoids into a four-part loop assembloid using 3D-printed wells.
• Utilized volumetric and mesoscale calcium imaging and extracellular recordings.
• Employed multi-step rabies retrograde tracing to map neuronal connectivity.

Main Results:

• Demonstrated the emergence of synchronized neuronal activity patterns within the loop assembloids.
• Confirmed the formation of functional neuronal connections across the reconstructed CSTC network.
• Identified aberrant synchronized activity in *ASH1L* loss-of-function models, relevant to autism spectrum disorder and Tourette syndrome.

Conclusions:

• The developed human multi-cellular platform provides unprecedented functional access to developing CSTC circuits.
• This platform is a valuable tool for studying early human brain development and neurological and psychiatric conditions.
• It enables the investigation of genetic contributions to CSTC circuit dysfunction in disease states.