iPSCs in Human Development Research
How are stem cells used in the research of human development?
What are their implications for drug research?
Overview
Induced pluripotent stem cells (iPSCs) can be used as a stem cell source to study human development and especially tissue and organ morphogenesis. Researchers are interested in the mechanisms behind how stem cells differentiate and self-organize into form tissues and organs. Other aspects of human development such as aging, cell signalling and cell death are also of great concern. By using stem cells to study the normal development of human body, researchers will be able to identify pathologies by comparing affected tissue with normal tissue and develop treatments accordingly.
Let’s use the following research as a case study to see how iPSCs can be used to study the development of eye, or in other words, ocular morphogenesis.
Case Study:
Co-ordinated Ocular Development From Human iPS Cells
and Recovery of Corneal Function
Hayashi, R., Ishikawa, Y., Sasamoto, Y., Katori, R., Nomura, N., Ichikawa, T., . . . Nishida, K. (2016).
Background
Severe eye diseases usually result in partial or complete loss of vision. Current solutions to severe eye diseases are limited and usually rely on the transplant of tissues such as cornea and lens. However, the demand for these tissues are significantly higher than the supply. Therefore, it is more ideal to develop therapies that are able to directly repair the damaged tissue and restore its function. In order to discover new therapies, scientists need to understand the normal morphogenesis of healthy tissue. By using iPS cells, scientists can obtain different types of cells and culture them to mimic the ocular morphogenesis.
Eye Anatomy
Figure 1: Anatomy of the eye
pupil: a small circular opening that allows light to come in
Iris: the colored part of the eye that controls the size of pupil by contraction
Cornea: clear outer layer of the Iris
Sclera: the white part of the eye, the outer layer
Lens: transparent tissue that focus light onto the retina
Retina: light-sensitive tissue consisted of neural cells that form colored image and the retinal pigment epithelium that protect the
retinal cells and vasculature
Optic nerve: obtain visual information from light and transmit to brain for the formation of visual images
The eye is roughly made up of four layers, each having different cell lineages. The innermost layer is the optic nerves consisted of neural cells. The second innermost layer is the retina, consisting of neural cells and the retinal pigment epithelium. Going further out are the lens and iris consisted of epithelial cells. The outermost layer is the sclera, consisting of surface epithelial cells.
My Channel
iPS Culture
Human iPS cells (hiPSC) programmed from skin and dermal fibroblasts were used in the research. During the first two weeks, hiPSCs were seeded onto plates and passaged in growth media. After that, they were cultured in differentiation media for about 4 weeks and then in corneal differentiation media for another 4 weeks.
Results
hiPSCs differentiated and organized into four concentric zones spontaneously in differentiation media. Let these four layers be 1, 2, 3, and 4 from the innermost to the outermost. Figure 2 shows a time-lapse image of the differentiation and organization of hiPSCs during the first 25 days in differentiation media. We can see that the cells from different layers have different morphologies, and as a result they formed clear lines distinguishing between each layer. The video below illustrates how hiPSCs differentiated and organized into four distinct layers during the first 25 days in culture.
Figure 2: Time-lapse image of the first 25 days in differentiation media
Time-lapse video of the first 25 days in differentiation media
By the end of 25 days in culture, four distinct layers formed, as shown in Figure 3. By studying the gene expression of the cells in these four layers, it was found that the cells from the four layers were from different lineages and these lineages resemble those in human eyes, as shown in Figure 4.
Zone 1
-
Innermost layer
-
Express neural cell gene markers, but no surface ectodermal markers → neural cells
-
Indicate central nervous system and neural cells
Zone 2
-
Express gene markers of neural crest cells and optic vesicle markers → neural cells and retinal pigment epithelial cells
-
Indicate retina and retinal pigment epithelium
Zone 3
-
No neural gene markers
-
Express ocular ectodermal gene markers→ ocular surface epithelium
-
Indicate lens
Zone 4
-
Express general ectodermal gene markers → outermost surface epithelium
-
Indicate sclera and cornea
Conclusion
Although this in vitro culture of ocular cells did not generate functional ocular tissue, it does mimic ocular development because the differentiated hiPSCs organized into 4 layers with different lineage, which resembles the sclera, lens, retina, retinal pigment epithelium and neural cells. Thus, the research has shown to facilitate the study of ocular morphogenesis and can be used for further study.
If you would like to read more about this research, please see the reference for a link to the paper.
Reference
Hayashi, R., Ishikawa, Y., Sasamoto, Y., Katori, R., Nomura, N., Ichikawa, T., . . . Nishida, K. (2016). Co-ordinated ocular development from human iPS cells and recovery of corneal function. Nature, 531(7594), 376-380. doi:10.1038/nature17000
<https://www.nature.com/articles/nature17000>
All figures and video presented on this page, if not otherwise cited, come from this paper.
Figure 1 credit to <https://en.wikipedia.org/wiki/Eye#/media/File:Schematic_diagram_of_the_human_eye_en.svg>
Figure 3 (left): Ocular morphology at the end of the 25th day in culture
Figure 4 (Above): Four layers resembling those in human eye
CNS, central nervous system; NE, neuroectoderm; OC, optic cup; NR, neuroretina; NC, neural crest; LE; lens; OSE, ocular surface ectoderm; SE, surface ectoderm; CE, corneal epithelium; EK, epidermal keratinocyte.
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