Divergence between neural and retinal lineage specification during human brain development by signal transduction

Abstract

Introduction: The physiological functions of p70 S6 kinase 1 (S6K1) have been extensively studied in S6K1-deficient mice. However, there is limited evidence demonstrating the influence of S6K1 deletion on human brain development.

Objectives: In this study, we identify the role of S6K1 in human brain development utilizing genetically engineered human embryonic stem cell-derived brain organoids.

Methods: Dorsal forebrain organoids generated from S6K1-depleted human embryonic stem cells (hESCs) were analyzed through single-cell RNA sequencing at early (5 weeks) and late (14 weeks) stages. In addition, the brain organoids derived from co-cultured S6K1-deleted and wild-type hESCs were subjected to ATAC-sequencing.

Results: Genetic deletion of S6K1 significantly decreases the size of the dorsal forebrain organoids in the early stages. Single-cell RNA sequencing analysis shows an abnormal emergence of retinal cell lineages in S6K1-deleted brain organoids, which diverges from cortical neurons in the early stage, eventually leading to a decrease in the proportion of mature cortical neurons. The chromatin accessibility analysis of co-cultured brain organoids shows that retinal specification in S6K1 knockout organoids was due to non-cell-autonomous function, whereas incomplete maturation of neurons results from cell-autonomous function.

Conclusion: Depletion of S6K1 signaling in the early stage of human brain development drives the formation of retinal cells distinct from cortical neurons. Our findings demonstrate that S6K1 signaling fine-tunes neuronal and retinal lineage specification during brain development.

Keywords: Brain organoids; Human brain development; Neuronal lineage specification; Retinal cell emergence; S6K1.