The People’s Guide to the Origin of Stem Cells
Three Main Categories of Stem Cells
Here we look at how stem cells are categorised based on the stages of the creation of life.
- Fertilisation
This is when a sperm from the father meets an egg from the mother, creating a single cell called a zygote. Found in the earliest stages after fertilisation, these cells can become any cell type in the body or the placenta.
- Cleavage
The zygote starts dividing into multiple cells without growing in size. This forms a cluster of cells called a blastocyst.
- Blastocyst Stage
By around day 5 after fertilisation, the blastocyst forms. It has two main parts: the inner cell mass (which will become the baby) and the outer layer (which will become the placenta).
- Inner Cell Mass
These cells are pluripotent stem cells, meaning they can turn into almost any cell type in the body but not the placenta. These cells later specialise into the three germ layers (ectoderm, mesoderm, and endoderm).
- Gastrulation
This is a crucial stage around week 3 of development. The inner cell mass forms three distinct layers called germ layers:
- Ectoderm: this layer forms the skin, nervous system, and parts of the eyes and ears.
- Neural Stem Cells: These stem cells originate from the ectoderm and can become various types of brain and nervous system cells.
- Mesoderm: This layer forms muscles, bones, blood, and connective tissues.
- Mesenchymal Stem Cells (MSCs): As the mesoderm forms, some cells within this layer develop into mesenchymal stem cells (MSCs). MSCs are multipotent stem cells, meaning they can turn into several types of cells, but only within a specific range.
- MSC Specialisation - Formation of Structures: During fetal development, MSCs are essential for forming the skeletal system, cartilage, and connective tissues.
- Migration and Differentiation: They can move to different parts of the developing body and become the specific cell types needed for forming and growing various tissues and organs.
- Endoderm: This layer forms the lining of the digestive and respiratory systems, liver, and pancreas.
- Endodermal Stem Cells: These stem cells come from the endoderm and can turn into cells that line organs and glands.
In simple terms, as a baby develops from a single fertilised egg, the different stages create various types of stem cells, each with unique potentials. The journey starts with totipotent cells that can become anything, moves to pluripotent cells that can become almost anything, and finally to multipotent cells that can specialise in specific tissues. Mesenchymal Stem Cells (MSCs) are a key type of multipotent stem cell, originating from the mesoderm and essential for forming various tissues in the body.
As we grow and develop from embryos into adults, our bodies go through many changes. One of these changes involves the types of stem cells we have. Here's why adults mainly have multipotent stem cells:
- Embryonic Stage:
- Early Versatility: In the early stages of development, we start with stem cells that are very versatile, like totipotent and pluripotent stem cells. These can turn into any type of cell needed to form a complete organism.
- Development into Specific Cells:
- Specialisation: As the embryo grows, these versatile stem cells gradually become more specialised. They start focusing on creating specific tissues and organs rather than being able to form any type of cell.
- Adult Stage:
- Multipotent Stem Cells: By the time we reach adulthood, our stem cells have become multipotent. This means they can only turn into a limited range of cells, specific to certain tissues or organs. For example, in adults, MSCs can become bone, cartilage, or fat cells but not nerve or liver cells.
Why Multipotent Stem Cells is Crucial for Adults?
- Specialisation for Repair:
- Efficient Repair: Multipotent stem cells are well-suited for maintaining and repairing specific types of tissues. They help keep our organs and tissues healthy and repair them when they are damaged.
- Less Risk:
- Controlled Function: Multipotent stem cells have a more controlled function, which reduces the risk of creating unwanted tissues or growths. This is important for maintaining the stability and safety of adult tissues.
- Focus on Maintenance:
- Tissue Maintenance: As adults, we need stem cells mainly for maintaining and repairing tissues rather than creating new types of cells. Multipotent stem cells are designed for this role, making them ideal for the needs of an adult body.
In short, as we mature, our bodies switch from having very versatile stem cells to having multipotent ones that are better suited for the maintenance and repair of specific tissues. This change helps ensure that stem cells work efficiently and safely in an adult body.
