Structural inheritance or cortical inheritance is the transmission of an

epigenetic In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...

trait in a living

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

by a self-perpetuating spatial structures. This is in contrast to the transmission of digital information such as is found in

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

sequences, which accounts for the vast majority of known genetic variation. Examples of structural inheritance include the propagation of

prion A prion () is a Proteinopathy, misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), w ...

s, the infectious proteins of diseases such as

scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known sin ...

(in sheep and goats),

bovine spongiform encephalopathy Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is an incurable and always fatal neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of th ...

('mad cow disease') and

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD) is an incurable, always fatal neurodegenerative disease belonging to the transmissible spongiform encephalopathy (TSE) group. Early symptoms include memory problems, behavioral changes, poor coordination, visu ...

(although the protein-only hypothesis of prion transmission has been considered contentious until recently). Prions based on heritable protein structure also exist in

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

. Structural inheritance has also been seen in the orientation of

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

in protozoans such as ''

Paramecium ''Paramecium'' ( , , plural "paramecia" only when used as a Common name, vernacular name) is a genus of eukaryotic, unicellular ciliates, widespread in freshwater, brackish, and Ocean, marine environments. Paramecia are often abundant in stagna ...

'' and ''

Tetrahymena ''Tetrahymena'' is a genus of free-living ciliates, examples of unicellular eukaryotes. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. ''Tetrahymena'' cel ...

'', and 'handedness' of the spiral of the cell in ''Tetrahymena'', and shells of snails. Some

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s also have structural inheritance, such as the

centriole In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers ( Pinophyta), flowering plants ( angiosperms) and most fungi, an ...

, and the

cell Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...

itself (defined by the

plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

) may also be an example of structural inheritance. To emphasize the difference of the molecular mechanism of structural inheritance from the canonical Watson-Crick base pairing mechanism of transmission of genetic information, the term 'epigenetic templating' was introduced.

History

Structural inheritance was discovered by Tracy Sonneborn, and other researchers, during his study on

protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...

in the late 1930s. Sonneborn demonstrated during his research on

that the structure of the cortex was not dependent on genes, or the liquid cytoplasm, but in the cortical structure of the surface of the ciliates. Preexisting cell surface structures provided a template that was passed on for many generations. John R. Preer, Jr., following up on Sonneborn's work, says, "The arrangement of surface structures is inherited, but how is not known, Macronuclei pass on many of their characteristics to new macronuclei, by an unknown and mysterious mechanism." Other researchers have come to the conclusion that "the phenomena of cortical inheritance (and related nongenic, epigenetic processes) remind us that the fundamental reproductive unit of life is not a nucleic acid molecule, but the remarkably versatile, intact, living cell." The study of structural inheritance is part of the

extended evolutionary synthesis The Extended Evolutionary Synthesis (EES) consists of a set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthe ...

In popular culture

An article in ''

Newsweek ''Newsweek'' is an American weekly news magazine based in New York City. Founded as a weekly print magazine in 1933, it was widely distributed during the 20th century and has had many notable editors-in-chief. It is currently co-owned by Dev P ...

'' mentions research that shows that "Some water fleas sport a spiny helmet that deters predators; others, with identical DNA sequences, have bare heads. What differs between the two is not their genes but their mothers' experiences. If mom had a run-in with predators, her offspring have helmets, an effect one wag called "bite the mother, fight the daughter." If mom lived her life unthreatened, her offspring have no helmets. Same DNA, different traits. Somehow, the experience of the mother, not only her DNA sequences, has been transmitted to her offspring." Various additional examples of structural inheritance are presented in the recent book '' Origination of Organismal Form''.

History

In popular culture

References

Further reading