Scientists create cell lineage maps of mouse embryos — Science News

Two groups of scientists used genome-editing methods to trace the origins of cells during the early development of mouse embryos. The researchers created the most detailed cell lineage maps to date for early mammalian development — up to the stage when organs begin to form in embryos, Science News reports.

Genetic labels for tracking cells

Both teams used prime editing, a method of modifying DNA. During embryonic development, marker sequences were added to the genomes of cells. Since daughter cells inherit changes from parental cells and accumulate new ones, scientists were able to reconstruct their family relationships.

The team led by molecular biologist Jonathan Weissman of the Massachusetts Institute of Technology introduced genetic instructions for the prime-editing system and 35 target DNA sites into the genomes of mouse embryonic stem cells. These cells were then added to mouse embryos at the four- to eight-cell stage. The researchers analyzed embryos aged from 7.5 to 10 days and reported the results in the journal Cell.

A map for 1.3 million cells

Another group, led by geneticist Jay Shendure of the University of Washington, used the DNA Typewriter approach. It adds six-nucleotide DNA fragments to a target sequence in a specific order, making it possible to determine the sequence of cell divisions.

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The scientists introduced the genetic instructions for this system into fertilized mouse eggs and allowed the embryos to develop to nearly 14 days of age. For one embryo, they compiled a cell lineage map for approximately 1.3 million cells. The work was published in the journal Science.

What the studies showed

The maps helped investigate the early formation of the nervous system. The Weissman team's analysis indicates that neural crest cells can still develop into different types of nerve cells at early stages of development.

Shendure's team also studied the phenomenon of clonal dominance, in which some early cells produce more descendants than others. It found that this inequality sharply increases at an early stage of the embryo's major restructuring. These maps may serve as a basis for research into organ formation, congenital defects, replacement cells, and evolution.