Exogenous

Exogenous
adj., [ɛk.ˈsɑd͡ʒ.ə.nəs]
Definition: produced or coming from the outside of an organism

Table of Contents

Exogenous Definition

Exogenous is a word referring to a factor or event coming or contributing from outside a defined system (physical or biological system).

Etymology

The word exogenous has been derived from three words.

An ancient Greek word and the prefix “exo” meaning ‘outside’ or ‘external’
A French word “-gene” meaning ‘produced from something’ (which is further derived from an ancient Greek word “-γενής”)
The Middle English word “ous” meaning ‘full of’ (which is derived forms of the Old Latin word “-ōsus”).

Biology definition:
Exogenous is a word referring to a factor or event coming or contributing from outside a defined system (physical or biological system). We often use the term exogenous for DNA, factors, DNA damage, and reproductive budding in the Biology subject.

What Is An Example Of Exogenous?

The word exogenous (adjective) is frequently used in Biology and Environmental Science to refer to stimulations, events, and processes occurring from/in the region outside the defined system. Such factors or events are called external factors or exogenous events.

Let’s look at some of the most relevant examples in sentences where the term is frequently used across different subjects.

Exogenous DNA

The word exogenous is quite frequently used in the context of the source of DNA; endogenous and exogenous DNA.

Exogenous DNA refers to the ‘DNA that originates from outside of an organism’ and is typically introduced artificially into cells. This can be done for a variety of reasons such as genetic engineering, gene therapy, or to study gene function.

Exogenous DNA can be introduced into cells using various techniques such as transformation, transfection, electroporation, microinjection, and viral vectors.

Fates of exogenous DNA:

- Once inside the cell, exogenous DNA can integrate into the host genome.
- Once inside the cell, exogenous DNA can exist as an episome, a circular piece of DNA that replicates independently of the host chromosome.
- Once inside the cell, the introduced exogenous DNA can also be transient, meaning it will only persist in the cell for a limited amount of time before being degraded or lost during cell division.

Uses: Exogenous DNA has revolutionized many fields of research including molecular biology, genetics, and biotechnology. It has allowed scientists to study gene function and regulation, develop new therapies for genetic diseases, and most importantly create genetically modified organisms for various purposes.

Concerns: There are several ethical concerns regarding the potential risks and unintended consequences of introducing foreign genetic material into organisms which requires scrutinized regulation. As such, there are strict regulations governing the use of exogenous DNA in research and medical applications, still, we need to amp up the regulatory guidelines from time to time.

Figure 1: Transformation, transduction and conjugation are different methods for the introduction of exogenous DNA. Image Credit: Microbiome Research Reports.

Can I introduce exogenous DNA (DNA-of-interest) into a zygote through a sperm?

Researchers have found out that by the tool of “ionic interactions”, the spermatozoa (sperm cells) can provide binding sites where exogenous DNA can bind. This finding has tapped the opportunity to introduce our DNA-of-interest into the zygote via sperms. This binding is usually reversible. As the exogenous DNA (foreign DNA or DNA-of-interest) binds to the sperm DNA, it can enter the oocyte (egg cell of a female) during the fertilization process. This transgenesis process has been speculated for experiments to produce transgenic animals. (Ref.1,2,3)

Figure 2: A workflow for sperm-mediated exogenous DNA introduction into a mouse model. Image Credit: Mufeed Ewadh.

Exogenous DNA Damage and Exogenous Factors

The word exogenous is also quite frequently used in the context of the mode of DNA damage; endogenous and exogenous DNA damage. DNA is the basic unit of inheritance that determines different aspects of most life forms on Earth. Any disruptions or damage to this molecule can lead to mutations that could lead to serious consequences. DNA is quite reactive and thus subject to modifications by endogenous and exogenous factors.

Exogenous DNA damage is defined as the damage caused to DNA by external factors like radiation, chemicals, and environmental toxins. These factors can cause changes to the DNA structure (exogenous change), resulting in mutations and other types of damage that can affect the proper functioning of cells and ultimately lead to diseases like cancer.

There are different types of exogenous DNA damage. Some examples of exogenous DNA damage are:

- Single-strand breaks
- Double-strand breaks
- Cross-linking
- Base damage

Figure 3: The figure shows different types of DNA damage; some of which are caused by internal factors while others are due to an exogenous shock. Image Credit: Google Sites.

Some examples of exogenous factors that cause DNA damage are:

- Exposure to ultraviolet (UV) radiation
- Exposure to ionizing radiation
- Oxidative stress
- Exposure to certain chemicals

The effects of exogenous DNA damage can be varied, ranging from mild to severe. This usually depends on the ‘extent of damage’ and the ‘type of cells affected’. In some cases, cells can repair the damage but in other cases, the damage may accumulate. This accumulation of damage often leads to cellular dysfunction, senescence (early aging), or apoptosis.

Figure 4: The picture provides a comprehensive description of different endogenous (inside factors) and exogenous (outside factors) factors that cause DNA damage and the related mechanism. Image Credit: ProteinTech.

Exogenous Budding

The word exogenous is also quite frequently used in the context of the mode of reproduction in Basic Biology lessons.

Exogenous budding is a process of cell division that occurs in certain organisms like some marine sponges (species of Scypha), some hydrozoans (species of Obelia and Hydra), yeast, and other fungi.

This is a typical asexual mode of reproduction where a small bud or outgrowth forms on the surface of the parent cell or such stems (exogenous bud growing exogenously).

Join us and participate in our Forum: Asexual and sexual reproduction differences

This protruding outgrown then grows and eventually separates from the parent cell to form a new, genetically identical daughter cell. Exogenous budding is an essential process for the growth and reproduction of these organisms. It allows for efficient cell division and enables the formation of colonies or chains of cells that can grow and thrive in various environments.

The process of exogenous budding is regulated by a complex network of genes and signaling pathways that control the formation and growth of the bud. Some of the most open-ended research areas where exogenous budding can be useful are:

- Cell Biology
- Genetics and biotechnology
- Development of new strategies for cell-based therapies
- Bio-manufacturing field

Figure 5: Exogenous budding across the diversity of life forms. Image Credit: Akanksha Saxena of Biology Online (adapted from the University of Oklahoma, Florida State University, Maricopa College, and the University of Edinburgh).

Exogenous Variable

The word exogenous is also used in subjects other than biology like economics. An exogenous variable is a variable that is outside the control of a system being studied or analyzed. It is a factor that is not affected by other variables within the system (similar to independent variables) but rather influences them. Exogenous variables are often used in statistical models to explain or predict changes in a dependent variable.

Some examples of exogenous variables include:

- Environmental factors
- Economic indicators
- Demographic characteristics

Importance of exogenous variables: Some of the most important roles are:

- They play a crucial role in economic models as they help explain and predict changes in economic systems.
- Economic models often use exogenous variables to represent external factors such as changes in government policies, economic shocks, or changes in global market conditions.
- By including exogenous variables in economic models, researchers can ‘better understand the impact of external factors on the economy’ and ‘predict how the economy will respond to different scenarios’.
- This information is important for policymakers, investors, and businesses as it can help them make informed decisions and develop strategies that are responsive to changes in the economic environment.

Figure 6: Exogenous variables in Economics. Image Credit: Matveeva.

Watch this vid about the exogenous antigen process (example of an exogenous biological event):

Take the Exogenous – Biology Quiz!

References

Lavitrano, M., French, D., Zani, M., Frati, L., & Spadafora, C. (1992). The interaction between exogenous DNA and sperm cells. Molecular reproduction and development, 31(3), 161-169.
Lavitrano, M., Giovannoni, R., & Cerrito, M. G. (2013). Methods for sperm-mediated gene transfer. Spermatogenesis: Methods and Protocols, 519-529.
Lavitrano, M., Busnelli, M., Cerrito, M. G., Giovannoni, R., Manzini, S., & Vargiolu, A. (2006). Sperm-mediated gene transfer. Reproduction, fertility, and development, 18(1-2), 19–23. https://doi.org/10.1071/rd05124
Chatterjee, N., & Walker, G. C. (2017). Mechanisms of DNA damage, repair and mutagenesis. Environmental and molecular mutagenesis, 58(5), 235. https://doi.org/10.1002/em.22087
Singleton, W. (2018). Invertebrate reproduction and development. Scientific e-Resources.