“Living cells continuously measure, process, and store cellular and environmental information.” ~ Swiss biologists Simon Ausländer & Martin Fussenegger
Cells constantly sense their own health and level of stress. Various proteins, such as filamentous actin, act as sensors. Signals are passed to the cytoskeleton and into the endoplasmic reticulum, which decide how to respond, and then let the rest of the cell know what to do.
“Living cells are complex systems that are constantly making decisions in response to internal or external signals; like a table around which decision makers debate and respond collectively to information put to them.” ~ French biologist Emmanuel Levy
Cells know and control the size and composition of their organelles to meet immediate needs, and to efficaciously allocate resources. There are both dedicated reporters of organelle condition and indirect functional readouts. These are used to optimize organelles during normal and stressful conditions.
Through the extracellular matrix, cells sense their external environment: both chemical and mechanical characteristics. A stem cell relies upon this information to determine what type of cell it should become.
Certain cell proteins have receptors which discern a variety of chemical attributes. Others sense external softness or stiffness based upon the mechanical stress applied to bonds that proteins put out.
It is critical for cells, whether microbial or part of a larger organism, to adaptively configure their biochemical operations to current conditions. Cells do so through a host of measures, including altering protein production and self-manipulating their DNA. All cells intelligently manage their lives at the molecular level.
If a cell is unable to make copies of its DNA, or if it overlooks mistakes in the DNA code, the result can be the production of cancerous cells or cell death. So, cells continuously monitor their DNA for damage.
Cells are flexible in managing their DNA. When the normal tools of DNA replication are damaged, cells adaptively try to work around the problem.
Cells communicate through protein pathways. Especially in the embryo, and during times of stress, quick decisions must be made. Through a variety of techniques, cell networks rapidly perform analog computations using optimal decision theory algorithms. Based upon inputs from cells, an intercellular network cooperatively decides a proper response to a situation and disseminates its decision to its member cells.
An astonishing example of cell intelligence occurs during multicellular organism development. Morphogenesis is the process of how a heritable body plan grows from a single-cell embryo, through various stages, into an adult. From a single cell emerges a diversity of cell types and tissues which appear in a strictly regulated sequence.
A mother stem cell can mint a daughter cell that is genetically identical yet given a different cell fate based upon immediate developmental need. This it knows by information from its external environment, combined with knowledge from its vast genomic encyclopedia within and the ability to distinguish slight chromosomal and epigenetic differences. The information processing capability of cells exceeds what the human mind can consciously comprehend.
A human embryo begins with a single cell that relentlessly divides, creating more cells. All of these are pluripotent stem cells, able to differentiate into any cell type.
7 days into embryogenesis, cells begin to specialize, crafting tissues and organs. Cues from 2 distinct vectors determine morphogenesis: one is chemical, the other geometrical.
Energetic/genetic developmental plans include geographic arrangement. Cells know what is expected of them by where they are physically situated.
Further, cells know how large they are, and the precise topography of neighboring cells, including those of different types. They carry in their minds detailed 3d maps of what is and what should be (the genetic “standard” plan). Such extensive memory is necessary because cells may act as service providers to cells of another type.
Using their knowledge, cells self-organize. This is how tissues are built. Extracellular networking and cell adhesion molecules play constitutive roles.
Wounds heal by regeneration. Regeneration occurs as cells recreate their lost brethren. Muscle cells create more muscle cells. Cartilage cells reproduce their own kind. All types of cells regenerate in the same intricate mixture as before the wound. Wound healing is only possible because cells know the schematic plan of the body in which they belong.
Until recently, cytologists wrongly thought that only pluripotent stem cells were able to facilitate wound repair. Instead, a somatic cell can differentiate into a different cell type if need be. Altering gene expression can turn one cell type into another. This process requires that cells recognize the situation and act accordingly.
In salamanders, dermal (skin) cells can regenerate either more skin or cartilage. Newts, but not salamanders, can regenerate lost eyes via somatic cells of different types.
Cell relationships are commonly symbiotic. Different types of cells actively cooperate to deal with a wound.
Scars occur because the regeneration system is less than perfect. In animals, ATP leaks from damaged cells. It is converted to adenosine, which promotes healing.
A scar forms when adenosine continues to be produced at a wound site after the injury has already healed, leading to a larger, thicker scar than what otherwise may have been.
Scarring is also an artifact of the cellular memory system, for remembrance as well as structural reinforcement. Scarring shows that cells absorb environmental influences.
Unless wound damage is severe, most scars appear cosmetic, and do not significantly affect function. To retain memory without impairing function, if possible, is a subtlety of healing.
Another reason for knowing the neighborhood is keeping invaders out. Cells sense when they are being fiddled with and respond to rid themselves of the nuisance.
Salmonella bacteria invade by injecting pathogenic proteins into a cell after breaking and entering using certain host enzymes. Salmonella prevent lysosomes, which are the first line of cellular defense, from getting the supply of toxic enzymes they need to do their jobs. Robbed of their ammunition, lysosomes become ineffective.
An assaulted cell recognizes the attack and sounds the alarm. This is an innate immune system response. Recognition and communication happen through various proteins working together in their various roles under cellular directive.
As a defense, the human blood-brain barrier separates blood from brain extracellular fluid. Brain infections are rare because of it and the encasement of the brain in a protective membrane.
For every tumor that originates in the brain, 10 make their way from other organs. They enter in disguise.
Deception is a common ruse for pathogens. Cancer cells lie about who they are in order to spread. To enter the brain, breast cancer cells conceal themselves by impersonating neurons. Cancer cells know where they are and take the cagey steps necessary to gain illicit entry.
Via elaborate communications, cancer cells distribute tasks, share resources, differentiate, and decide how to proceed. Before sending cells to colonize tissues and organs (metastasis) spy cells are sent out reconnoiter the situation and report back. Only with hopeful prospects do metastatic cells leave a tumor and navigate to new posts. If they sense danger, cancer cells become dormant, then reactivate at will when conditions warrant.
Cancer cells change their environment to suit their needs, inducing genetic changes and enslaving surrounding cells. Cancers may fuse with other cells, or otherwise obtain the knowledge and equipment they need to metastasize. Having gone bad, cancer cells use wiles and determination to take down their host.
“Cancer causes aging. Cancer cells drive the aging process in neighbouring non-cancer cells.” ~ English cytologist Stuart Rushworth