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

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.

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

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.

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.

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.