Developmental trajectory of functional neocortical networks in an in vitro mouse model of Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function MECP2 mutations, affecting ~1 in 10,000 female births. RTT causes progressive impairments in early life and has no cure. Despite known genetic origin in RTT, the mechanisms by which MECP2 mutations disrupt brain function is poorly understood. Compared to molecular or cellular studies, microscale network analysis may reveal how genetic mutations influence neuronal circuitry relevant to behaviour. Investigating how microscale functional networks are disrupted in RTT in humans remains challenging. In contrast, Mecp2-deficient mice recapitulate RTT-like features and reveal early synaptic deficits. However, how these synaptic disruptions translate into aberrant network-level development remains unclear. To address this gap, my thesis characterises the early development of neocortical functional network activity and topology with single-cell resolution in a mouse model of RTT. Also, my thesis aims to disentangle cell-autonomous and non-cell-autonomous contributions to dysfunction in mosaic Mecp2-heterozygous (Mecp2-Het) networks, by comparing Mecp2-positive and Mecp2-negative neurons. Due to the challenges of in vivo imaging during early brain development, I used primary cortical cultures from wild-type, Mecp2-Het and Mecp2-hemizygous (Mecp2-KO) littermates. I recorded spontaneous neuronal activity from days-in-vitro (DIV) 14 to 42 using calcium imaging, followed by identification of Mecp2 expression with immunofluorescent staining. I found that Mecp2-KO networks showed hyperactivity, with increased event rates, more active cells, shorter inter-event intervals, and reduced event durations, while Mecp2-Het networks displayed intermediate profiles with preserved activity patterns. Mecp2-deficient networks also showed premature maturation followed by early plateau or decline in functional connectivity and network topology, including network density, and local and global efficiency. These effects were more pronounced in Mecp2-KO networks than Mecp2-Het networks, reflecting distinct pathophysiological mechanisms. These network-level disruptions were evident from DIV14, preceding behavioural deficits at 8 weeks in vivo. Critically, disrupted network development was driven predominantly by non-cell-autonomous interactions. Together, these findings demonstrate that microscale neocortical networks recapitulate key topological features of brain-wide organisation and are profoundly disrupted by Mecp2 deficiency, driven largely by non-cell-autonomous mechanisms. They underscore the importance to consider network-level contributions in designing RTT therapeutic strategies.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Yuan, Yin

Advisor dc:contributor.advisor

• Paulsen, Ole

• Neuroscience
• Neuronal network
• Rett Syndrome
• Neurodevelopmental disorders

Licence

• https://www.repository.cam.ac.uk/bitstreams/4c86090e-ffe9-4ebb-93ef-a846e27c3cff/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.125279

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/395931