# An in vivo and in vitro spatiotemporal profile of human midbrain development

## TL;DR

This study compares fetal human midbrain development with lab-grown models to assess their similarity and usefulness in studying dopamine-related disorders.

## Contribution

The study provides a spatiotemporal profile of fetal midbrain development and validates midbrain organoids as relevant models for dopamine-related disorders.

## Key findings

- Fetal midbrain tissue by the second trimester shows structural complexity similar to adults.
- Midbrain organoids closely resemble late first trimester tissue in cellular composition.
- Spatial transcriptomics reveals that organoids capture the architecture and signaling of second trimester midbrain.

## Abstract

The dopaminergic system has key roles in human physiology and is implicated in a broad range of neurological and neuropsychiatric conditions that are increasingly investigated using induced pluripotent stem cell-derived midbrain models. To determine similarities of such models to human systems, here we undertake single-cell and spatial profiling of first and second trimester fetal midbrain and compare it to in vitro midbrain models. Histological examination reveals that, by the second trimester, fetal midbrain tissue exhibits structural complexity comparable to that of adults. At the molecular level, single-cell profiling uncovers differences in cellular composition across models, with brain organoids most closely resembling late first trimester tissue — an observation supported by meta-integration of existing midbrain datasets. By reconstructing developmental trajectories of neuronal and astrocytic lineages, we map gene expression dynamics associated with maturation. Importantly, integration of spatial transcriptomics provides critical context for aligning organoid models, revealing that their spatial organization and intercellular signaling resemble the architecture and microenvironment of the second trimester midbrain. Ultimately, we leverage our findings to study Dopamine Transporter Deficiency Syndrome progression in patient-derived midbrain organoids, validating their relevance. Understanding the extent of human tissue recapitulation in midbrain laboratory models is essential to justify their use as biological proxies.

This study provides a comprehensive profile of human fetal midbrain development and its comparison with lab-grown midbrain cultures. These findings demonstrate that midbrain organoids recapitulate fetal developmental stages while capturing essential spatial and molecular characteristics, relevant to dopamine-related disorders.