Somatic mutations reveal asymmetric cellular dynamics in the early human embryo

Area of Science:

• Genetics
• Developmental Biology
• Genomic Medicine

Background:

• Somatic cells accumulate mutations throughout life.
• Early embryonic mutations can cause genetic diseases, predispose to cancer, and transmit to offspring.
• Understanding early embryonic somatic mutations is limited, despite known chromosomal abnormalities in early embryos.

Purpose of the Study:

• To identify and characterize early embryonic mutations in humans.
• To estimate mutation rates during early human embryogenesis.
• To reconstruct developmental lineages and understand cell contributions to adult tissues.

Main Methods:

• Whole-genome sequencing of normal blood from 241 adults.
• Identification of 163 early embryonic mutations.
• Analysis of mutational signatures and developmental lineage reconstruction.

Main Results:

• Approximately three base substitution mutations occur per cell per cell-doubling event in early human embryogenesis.
• Identified mutations are primarily attributed to two known mutational signatures.
• Demonstrated asymmetric contribution (approx. 2:1 ratio) of early cell-doubling daughter cells to adult blood.

Conclusions:

• Early human embryogenesis involves significant mutation accumulation.
• Mosaic mutations provide insights into early cell lineages and their contribution to adult tissues.
• Asymmetric cell division patterns are evident in early human development and contribute to adult tissue composition.