Cellular differentiation

Cellular differentiation is the process where a stem cell changes into a more special type of cell. This happens many times as a multicellular organism grows from a simple zygote into a complex group of tissues and different cell types. Even after we are born, differentiation continues when adult stem cells divide and make new cells to fix tissues and replace old ones.

This process changes a cell’s size, shape, membrane potential, metabolic activity, and how it reacts to signals. These changes are mostly because of controlled changes in gene expression, a field called epigenetics. These changes do not change the DNA order, but the cell’s makeup changes a lot. Because of this, different cells can look and work very differently even though they all have the same genome.

There are different levels of how much a cell can change into other types, called cell potency. A totipotent cell can become any cell type, including placental tissue. In mammals, only the zygote and early blastomeres are totipotent. A pluripotent cell can become any cell type in the adult body, such as embryonic stem cells in animals. Other cells can only become a few related types and are called multipotent, oligopotent cells, or unipotent depending on how many types they can become.

Mammalian cell types

See also: List of distinct cell types in the adult human body

Our bodies are made up of three main types of cells: germ cells, somatic cells, and stem cells. Humans have many cells, each with its own copy of the genome, except for red blood cells which do not have nuclei. Most cells are diploid, meaning they have two copies of each chromosome. These somatic cells form most of the body, like skin and muscle cells, and they specialize for different jobs through a process called differentiation.

Germ cells make gametes—eggs and sperm—and continue through generations. Stem cells can divide many times and create special cells. After a sperm joins an egg, the new cell divides and forms a blastocyst. Inside the blastocyst is a group of cells called the inner cell mass that can become almost any cell type in the body. These cells are pluripotent and later become multipotent progenitor cells, which then develop into working cells like neurons, blood cells, and bone cells.

Dedifferentiation

Dedifferentiation, or integration, is when a specialized cell changes back to a simpler form. This can happen in some animals like worms and amphibians to help them heal or grow new body parts. It can also occur in plant cells and in cells grown in a lab.

Scientists found that a molecule called reversine can cause dedifferentiation in some cells. These cells then act more like stem cells and can change into different types of cells again, such as bone-building cells known as osteoblasts or fat cells called adipocytes. Some people think dedifferentiation might be linked to cancers, while others believe it is a natural part of how the immune system works.

Mechanisms

See also: Embryonic differentiation waves

Cells change from one type to another by turning some genes on and off. Special networks guide which genes are active in a cell. These networks help make the many different cell types in our bodies.

Cells also get signals from other cells. These signals tell them what to become. The signals can cause changes inside the cell, helping it specialize. When a cell divides, the two new cells can become different types right away. This helps create patterns and structures as an organism grows.

Epigenetic control

Main article: Epigenetics in stem cell differentiation

All cells in your body have the same instructions, or genes. But different cells, like skin cells or brain cells, act in different ways. This happens because of a process called epigenetic control. It helps decide which genes are turned on or off, guiding a cell to become a specific type.

Epigenetic control is important for cells to know what they should become. For example, studies with special types of stem cells show that these cells have chemical tags—called DNA methylation. These tags help keep the cells flexible and able to develop into many different types. Scientists study these tags to learn how cells decide their roles during growth.

Evolutionary history

See also: Bangiomorpha

A very old, simple creature called Bicellum brasieri lived over a billion years ago. It had two different kinds of cells. This shows that cells can change and specialize, which helps create many types of life. This probably started in freshwater lakes.