Around the time of birth, the developing human brain purges itself of a vast number of mutation-riddled neurons, according to a detailed analysis of more than 2,300 nerve cells published in Nature on October 28. This cellular cleanup sheds light on a previously unknown mechanism that regulates brain cell counts and shapes the genetic makeup of the human cerebral cortex.
Fetal Brain Analysis Reveals Widespread Chromosomal Abnormalities
More than one-quarter of the sampled neurons from the brains of human fetuses had either gained or lost several segments of their chromosomes. By contrast, only about 6% of neurons from the brains of babies after birth carried such structural abnormalities. Christos Proukakis, a neurologist at University College London who was not involved in the research, noted that the surviving neurons appear to be those with the most intact genomes during development.
Diane Shao, a paediatric neurogeneticist at Boston Children’s Hospital in Massachusetts and first author on the study, explained that the findings point to a novel quality-control process. This mechanism decides which fetal nerve cells persist in the brain and which are eliminated before birth.
Tracking Copy Number Variation Across Human Development
To map this developmental shift, Shao and her colleagues analyzed the brains of deceased individuals ranging from fetuses at 14 weeks of gestation to nonagenarians. The research team focused specifically on neurons in the cerebral cortex, the region responsible for memory, learning, and consciousness. They searched for copy number variation, a phenomenon where individual neurons have lost or gained chromosomal segments.
Did you know? Researchers spent years verifying the initial data because the sheer volume of cells with widespread copy number variation during fetal development was so unexpectedly high. Even after repeating the experiment using an alternative single-cell sequencing method, the results remained consistent.
After birth, the proportion of these abnormal neurons dropped by more than fourfold. This steep decline indicates that the cells with damaged or altered genomes were systematically culled during early development.
Synapse Formation and Potential Links to Childhood Neurological Conditions
The biological triggers that identify which brain cells are normal remain under investigation. However, Shao pointed to a potential clue: neurons exhibiting high levels of copy number variation also tended to show abnormal activity in genes responsible for forming synapses—the crucial connections that allow brain cells to communicate with one another.
Understanding this pruning process could eventually provide critical insights into neurological conditions that manifest in childhood, such as autism spectrum disorder and epilepsy.
Common Questions About Fetal Neuron Pruning
Which brain region did the researchers study?
The research team focused on neurons located in the cerebral cortex, which governs learning, memory, and consciousness.
What percentage of neurons showed abnormalities after birth?
Only about 6% of neurons sampled from the brains of babies after birth carried chromosomal gains or losses, compared to more than 25% during the fetal stage.
When was the study published?
The findings were published in the journal Nature on October 28.
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