All humans begin life as a single cell that divides repeatedly to form two, then four, then eight cells, all the way up to the ~26 billion cells that make up a newborn. Tracing how and when those 26 billion cells arise from one zygote is the grand challenge of developmental biology, a field that has so far only been able to capture and analyze snapshots of the development process.
Now, a new method developed by scientists finally brings that daunting task into the realm of possibility using evolving genetic barcodes that actively record the process of cell division in developing mice, enabling the lineage of every cell in a mouse's body to be traced back to its single-celled origin. The research is published in Science.
"Current lineage-tracking methods can only show snapshots in time, because you have to physically stop the development process to see how the cells look at each stage, almost like looking at individual frames of a motion picture," said senior author. "This barcode recording method allows us to reconstruct the complete history of every mature cell's development, which is like playing the full motion picture backwards in real-time."
The genetic barcodes are created using a special type of DNA sequence that encodes a modified RNA molecule called a homing guide RNA (hgRNA), which was developed in a previous paper. hgRNA molecules are engineered such that when the enzyme Cas9 (of CRISPR-Cas9 fame) is present, the hgRNA will guide the Cas9 to its own hgRNA sequence in the genome, which Cas9 then cuts. When the cell repairs that cut, it can introduce genetic mutations in the hgRNA sequence, which accumulate over time to create a unique barcode.
The researchers implemented the hgRNA-Cas9 system in mice by creating a "founder mouse" that had 60 different hgRNA sequences scattered throughout its genome. They then crossed the founder mouse with mice that expressed the Cas9 protein, producing zygotes whose hgRNA sequences started being cut and mutated shortly after fertilization.
"In every single cell that the zygote divides to become, there's a chance that its hgRNAs will mutate," explained first author. "In each generation, all the cells acquire their own unique mutations in addition to the ones they inherit from their mother cell, so we can trace how closely related different cells are by comparing which mutations they have."
Each hgRNA can produce hundreds of mutant alleles; collectively, they can generate a unique barcode that contains the full developmental lineage of each of the ~10 billion cells in an adult mouse.
The ability to continuously record cells' development also allowed the researchers to resolve a longstanding question regarding the embryonic brain: does it distinguish its front from its back end first, or its left from its right side first? By comparing the hgRNA mutation barcodes present in cells taken from different parts of two mice's brains, they found that neurons from the left side of each brain region are more closely related to neurons from the right side of the same region than to neurons from the left side of neighboring regions. This result suggested that front-back brain patterning emerges before left-right patterning in the development of the central nervous system.
"This method allows us to take the final developmental stage of a model organism and from there reconstruct a full lineage tree all the way back to its single-cell stage. It's an ambitious goal that will certainly take many labs several years to realize, but this paper represents an important step in getting there," said the author. The researchers are now focusing on improving their readout techniques so that they can analyze the barcodes of individual cells and reconstruct the lineage tree that has been recorded.
"Being able to record cells continuously over time is a huge milestone in developmental biology that promises to exponentially increase our understanding of the process by which a single cell grows to form to an adult animal and, if applied to disease models, it could provide entirely new insights into how diseases, such as cancer, emerge," said another author.
https://wyss.harvard.edu/recording-every-cells-history-in-real-time-with-evolving-genetic-barcodes/
http://science.sciencemag.org/content/early/2018/08/08/science.aat9804
Genetic barcodes to record every cell's history in real-time
- 1,872 views
- Added
Edited
Latest News
A drug to prevent flu-induc…
By newseditor
Posted 18 Apr
New origin of deep brain waves
By newseditor
Posted 17 Apr
Starving cells hijack prote…
By newseditor
Posted 17 Apr
Miniature battery-free epid…
By newseditor
Posted 17 Apr
Molecular causes of differe…
By newseditor
Posted 16 Apr
Other Top Stories
A wireless closed-loop system for optogenetic peripheral neuromodul…
Read more
Detecting Alzheimer's disease six months before diagnosis using AI
Read more
Inhalable form of messenger RNA created!
Read more
Safer and more efficient gene editing!
Read more
LEDs to improve health, food!
Read more
Protocols
MemPrep, a new technology f…
By newseditor
Posted 08 Apr
A tangible method to assess…
By newseditor
Posted 08 Apr
Stem cell-derived vessels-o…
By newseditor
Posted 06 Apr
Single-cell biclustering fo…
By newseditor
Posted 01 Apr
Modular dual-color BiAD sen…
By newseditor
Posted 31 Mar
Publications
How does the microbiota con…
By newseditor
Posted 18 Apr
The integrated stress respo…
By newseditor
Posted 18 Apr
The immunobiology of herpes…
By newseditor
Posted 17 Apr
Circulating microbiome DNA…
By newseditor
Posted 17 Apr
Spindle oscillations in com…
By newseditor
Posted 17 Apr
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar