A cell type is a classification used to identify cells that share morphological or

phenotypical In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

features. A

multicellular organism A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially un ...

may contain cells of a number of widely differing and specialized cell types, such as

muscle cell A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a m ...

s and skin cells, that differ both in appearance and function yet have identical genomic sequences. Cells may have the same

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

, but belong to different cell types due to the differential

regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology Biology is the scientific study of life. It is a natural science with a ...

of the

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s they contain.

Classification Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. Classification is the grouping of related facts into classes. It may also refer to: Business, organizat ...

of a specific cell type is often done through the use of

microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of mi ...

(such as those from the

cluster of differentiation The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophen ...

family that are commonly used for this purpose in

immunology Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see ther ...

). Recent developments in single cell RNA sequencing facilitated classification of cell types based on shared gene expression patterns. This has led to the discovery of many new cell types in e.g. mouse cortex,

hippocampus The hippocampus (via Latin from Greek , ' seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, ...

dorsal root ganglion A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dor ...

and

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...

. Animals have evolved a greater diversity of cell types in a

multicellular A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially un ...

body (100–150 different cell types), compared with 10–20 in plants, fungi, and protists. The exact number of cell types is, however, undefined, and the Cell Ontology, as of 2021, lists over 2,300 different cell types.

Multicellular organisms

All higher

organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...

s contain cells specialised for different functions. Most distinct cell types arise from a single

totipotent Pluripotency: These are the cells that can generate into any of the three Germ layers which imply Endodermal, Mesodermal, and Ectodermal cells except tissues like the placenta. According to Latin terms, Pluripotentia means the ability for many thin ...

cell that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

s during division).

Multicellular organisms A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially u ...

are composed of cells that fall into two fundamental types: germ cells and somatic cells. During development, somatic cells will become more specialized and form the three primary

germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three pr ...

s: ectoderm,

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...

, and endoderm. After formation of the three

s, cells will continue to specialize until they reach a terminally differentiated state that is much more resistant to changes in cell type than its

progenitors In genealogy, the progenitor (rarer: primogenitor; german: Stammvater or ''Ahnherr'') is the – sometimes legendary – founder of a family, line of descent, clan or tribe, noble house, or ethnic group.. Ebenda''Ahnherr:''"Stammvater eines ...

Conceptual definition

Even though the concept of cell type is widely used, specialists still discuss the exact definition of what constitutes a cell type.

Humans

A list of cell types in the human body may include several hundred distinct types depending on the source.

References

External links

*{{Commons category-inline, Cell types Developmental biology

Multicellular organisms

Conceptual definition

Humans

See also

References

Further reading

External links