Background <p>Developmental dyslexia (DD) is a common learning disorder with significant consequences for affected individuals. Although several candidate genes, including dyslexia susceptibility 1 candidate 1 (DYX1C1), have been implicated in dyslexia, their role in brain development remains unclear. We aimed to elucidate the spatiotemporal expression patterns of DYX1C1 during cerebral cortex development in rats.</p> Methods <p>We investigated DYX1C1 expression during cerebral cortex development using rat embryos at various gestational stages (E13.5, 15.5, 17.5 and 20.5) by immunohistochemistry (<i>n</i> = 7 embryos/stage), quantitative real-time PCR (<i>n</i> = 6), and in situ hybridization (<i>n</i> = 11–15).</p> Results <p>The DYX1C1-positive cells were predominantly located in the outermost layers of the cortical plate, particularly at E15.5. DYX1C1 mRNA expression peaked at E15.5 and subsequently declined. DYX1C1-positive cells did not co-localize with reelin-positive Cajal-Retzius cells, but co-localized with neuronal markers expressed during development, and had shorter primary cilia than DYX1C1-negative cells.</p> Conclusions <p>Our findings highlight the dynamic expression of DYX1C1 in the developing cerebral cortex of rats, implicating its involvement in neurodevelopmental processes. Further investigation of the functional interactions of DYX1C1, particularly its relationship with reelin and its role in cerebrocortical and hippocampal development, may provide insights into the pathophysiology of dyslexia and neurodevelopmental disorders.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Our study elucidates spatiotemporal expression patterns of endogenous DYX1C1 predominantly in the primitive cortical zone (PCZ), outermost layer of the cortical plate (CP) during cerebral cortex development, particularly peaked at E15.5.</p> </ItemContent> <ItemContent> <p>We revealed the spatial relationship between DYX1C1-positive and reelin-expressing Cajal-Retzius (CR) cells, and co-localize with neuronal markers expressed during cerebral cortex development, indicating its contribution to neuronal migration and cortical layer formation.</p> </ItemContent> <ItemContent> <p>DYX1C1-positive cells mainly in the PCZ possess shorter primary cilia than DYX1C1-negative cells, suggesting the completion of migration.</p> </ItemContent> </UnorderedList></p>