Large-scale EM Data Reveals Myelinated Axonal Changes and Altered Connectivity in the Corpus Callosum of an Autism Mouse Model

Guoqiang Zhao ^1,2 Ao Cheng ³ Jiahao Shi ^1,2 Peiyao Shi ² Jun Guo ⁴ Chunying Yin ⁴ Hafsh Khan ^1,2 Jiachi Chen ^1,2 Pengcheng Wang ^1,2 Jiao Chen ^1,2 Ruobing Zhang ^2*

• ¹ School of Biomedical Engineering (Suzhou), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China
• ² Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences (CAS), Suzhou, Jiangsu Province, China
• ³ School of Electronic and Information Engineering, Soochow University, Suzhou, Jiangsu Province, China
• ⁴ Institute of Artificial Intelligence, Hefei Comprehensive National Science Center, Hefei, Anhui Province, China

Autism spectrum disorder (ASD) encompasses a diverse range of neurodevelopmental disorders with complex etiologies, including genetic, environmental, and neuroanatomical factors. While the exact mechanisms underlying ASD remain unclear, structural abnormalities in the brain offer valuable insights into its pathophysiology. This study investigated ultrastructural changes in the corpus callosum of Shank3B heterozygous mouse, a model for ASD, using serial scanning electron microscopy (sSEM). A dataset of the entire sagittal sections of the corpus callosum from wild-type and Shank3B mutant mice was acquired at 4 nm resolution, enabling precise comparisons of myelinated axon properties. Leveraging a fine-tuned EM-SAM model for automated segmentation, we quantitatively analyzed key metrics, including G-ratio, myelin thickness, and axonal density. Statistical analyses revealed significant global alterations in Shank3B mouse, highlighting abnormalities in myelinated axon structure and connectivity within the corpus callosum. These findings provide critical insights into the microstructural basis of ASD and offer new perspectives on its underlying neural mechanisms.