Cell heterogeneity is the result of genetic variation and the biological difference between cells of different types as well as the same type or population and can be due to various factors.
Cell heterogeneity can be both effective, with epigenetic changes being critical for normal development, as well as concerning, due to cell heterogeneity being responsible for cancer heterogeneity. The significance of biological variation within cells will be further explored in this article for genomic research.
Background: What Is the Genome?
Genomic research consists of the study of the genome, which includes all the genes within a person, as well as the interaction of these genes with each other and the environment.
The complete collection of DNA is known as the genome, and this can be found in almost every cell in the body, with an estimated number of three million DNA base pairs being found. The base pairs are the biological building blocks that form DNA, with the four main nucleotide bases being adenine, thymine, cytosine and guanine.
DNA encompasses all information found in the body, with instructions to build proteins and maintain cellular mechanisms; a gene can be described as a unit of DNA and there are approximately between 20,000 and 25,000 genes found in the human genome.
The base pairs are used to form amino acid chains, which ultimately code for proteins. There are 20 amino acids in the standard genetic code and variations of these code for approximately 10,000 different proteins.
Heterogeneity is significant within cells as variations in nucleotide base pair sequences can lead to variations in amino acid sequences, resulting in different proteins.
While all cells carry the same DNA, different types of cells have various genes that are ‘switched on’ or ‘switched off’, allowing them to carry out different functions within the body.
Additionally, epigenetic changes, which consist of phenotypical influences affecting gene expression, can modify the status of genes, causing them to become activated or silenced. This epigenetic modulation can lead to disease progression and tumorigenesis.
The study of the genome has enabled cells of different and the same populations to be investigated. An example of this can be found in embryonic stem cells, which illustrates how heterogeneity within expression can result in cell differentiation and different population types.
Cell-to-cell heterogeneity within gene expression has been a branch of genomic research that has gained traction over the years, with an active investigation to uncover this biological mystery.
With multiple mechanisms being associated with this concept and gene expression, there can be a multitude of factors that result in heterogeneity, from the way DNA transcription occurs, which involves the replication of a DNA template, to gene activation and repression, the influence of the environment, as well as transcription factors.
Significance of Cell Heterogeneity
The importance of all these concepts can be found in the continual study of human disease.
While there can be large populations of the same cell type, there is always a level of cell heterogeneity present, and this can have both minimal and major significance to a patient’s health. A collective behavior found in a large population of cells for a significant function may not always be found in singular or individual cells within that population.
This concept has resulted in genetic analyses focusing on single cells to find mechanisms that have been missed when analyzing a large sample. Single-cell sequencing can be more useful than bulk cell sequencing methods due to deep sequencing of individual cells through methods such as next-generation sequencing (NGS), which allows a more comprehensive insight into the genetic information and the function of a particular cell within its microenvironment.
Not all cancers are the same. While two people may have been diagnosed with the same type of cancer, such as lung cancer, this does not mean these patients should be given the same treatment.
The more comprehensive and effective method of diagnosing and treating patients include understanding the underlying mechanism behind the cancers of these patients, which should dictate the patient treatment plan. This type of treatment that considers the cellular heterogeneity of cancer cells furthers the field of precision medicine. It ensures the genetic mutations within the individual patient’s cancer are being treated.
The significance of cell heterogeneity for genomic research allows comprehensive genome analysis with effective detection of somatic mutations found in patients, including alterations such as point mutations, insertions and deletions, and gene fusions. This can then inform treatment, with precision treatment given to patients to treat the mutations that cause tumorigenesis rather than broad spectrum chemotherapy.
An example of this includes tyrosine kinase inhibitors for specific mutations that underlie certain cancer types such as non-small lung cancer.
The Future of Cell Heterogeneity: Precision Medicine
Understanding the cellular heterogeneity in healthy and diseased cells can further genomic research into how cells can mutate, the triggers for these mutations, and how the mutations can be treated specifically. This can result in a better prognosis as well as reduce disease progression and metastasis, which can occur with cancer treatments given to patients with resistant mutations.
Precision medicine upholds the individuality of patient disease and treatment and the study of cell heterogeneity for genomic research only enhances the cause for higher quality of care and treatment.
Further Reading and References
Altschuler, S. and Wu, L., (2010) Cellular Heterogeneity: Do Differences Make a Difference?. Cell, 141(4), pp. 559-563. https://pubmed.ncbi.nlm.nih.gov/20478246/
Carter, B. and Zhao, K., (2020) The epigenetic basis of cellular heterogeneity. Nature Reviews Genetics, 22(4), pp. 235-250. https://www.nature.com/articles/s41576-020-00300-0
A Brief Guide to Genomics. (2022) [Online] National Human Genome Research Institute. Available at: https://www.genome.gov/about-genomics/fact-sheets/A-Brief-Guide-to-Genomics
Hinohara, K. and Polyak, K., (2019) Intratumoral Heterogeneity: More Than Just Mutations. Trends in Cell Biology, 29(7), pp 569-579. https://www.cell.com/trends/cell-biology/fulltext/S0962-8924(19)30046-7
Lelièvre, S., Hodges, K. and Vidi, P., (2014) Application of Theranostics to Measure and Treat Cell Heterogeneity in Cancer. Cancer Theranostics, pp. 493-516. https://www.sciencedirect.com/science/article/abs/pii/B9780124077225000268?via%3Dihub
Verma, M. and Kumar, V., (2019) Single-Cell Epigenomics: Technology and Applications. Single-Cell Omics, pp.215-229. Available at: https://www.sciencedirect.com/science/article/abs/pii/B9780128149195000117?via%3Dihub
Yeh, C. and Hsu, C., 2019. Microfluidic Techniques for Single-Cell Culture. Single-Cell Omics, pp. 137-151. https://www.sciencedirect.com/science/article/abs/pii/B9780128149195000075?via%3Dihub