SPONTANEOUS <SPAN STYLE="MARGIN: 0PX; PADDING: 0PX;">NEURONAL</SPAN> ACTIVITY DRIVES GENE EXPRESSION PROGRAMS IN THE HUMAN FETAL CORTEX

Spontaneous neuronal activity is a hallmark of the neocortex development and is thought to shape cortical maturation and neuronal differentiation. In the human cortex, however, how spontaneous activity emerges during development and its influence on neuronal gene expression remain poorly understood.
Here, we established an organotypic culture system for fetal human cortical slices (Ethics: LL‑KT‑2022006‑1) and examined spontaneous neuronal activity and activity-dependent transcription after several days in vitro. Calcium imaging of cultured coronal slices revealed sparse spiking in the cortical plate (CP) at post-conception week (PCW) 13, followed by the emergence of locally synchronized events at PCW15–17. At later stages (>PCW20), tangentially propagating Ca²⁺ waves appeared in the CP and recurred at regular intervals. To test whether spontaneous activity drives transcriptional programs, we performed RNA-seq at the late developmental stages with or without tetrodotoxin. Blocking neuronal activity markedly reduced the expression of canonical immediate-early genes and late-response genes. Conversely, at early developmental stages, depolarization by elevated extracellular KCl robustly increased the expression of typical activity-dependent genes, supporting a causal role for intrinsic activity in transcriptional induction. Beyond these canonical programs, spontaneous neuronal activity also enhanced the expression of human-enriched and cell-type-specific genes.
Together, these results suggest that spontaneous activity progresses in the developing human cortex and contributes to both conserved activity-dependent transcription and the gene programs that may be involved in human cortical maturation.