medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...

, heterotopia is the presence of a particular tissue type at a non-physiological site, but usually co-existing with original tissue in its correct anatomical location. In other words, it implies ectopic tissue, in addition to retention of the original tissue type.

Examples

In neuropathology, for example, gray matter heterotopia is the presence of

gray matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguis ...

within the

cerebral white matter Cerebral may refer to: * Of or relating to the brain * Cerebrum, the largest and uppermost part of the brain * Cerebral cortex, the outer layer of the cerebrum * Retroflex consonant, also referred to as a cerebral consonant, a type of consonant so ...

or ventricles. Heterotopia within the brain is often divided into three groups: subependymal heterotopia, focal cortical heterotopia and band heterotopia. Another example is a

Meckel's diverticulum A Meckel's diverticulum, a true congenital diverticulum, is a slight bulge in the small intestine present at birth and a vestigial remnant of the omphalomesenteric duct (also called the vitelline duct or yolk stalk). It is the most common malformat ...

, which may contain heterotopic gastric or pancreatic tissue. In

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

specifically, ''heterotopy'' refers to an altered location of trait expression.West-Eberhard, 2003 In her book ''Developmental Plasticity and Evolution'', Mary-Jane West Eberhard has a cover art of the sulphur crested cockatoo and comments on the back cover "Did long crest eadfeathers evolve by gradual modification of ancestral head feathers? Or are they descendants of wing feathers, developmentally transplanted onto the head". This idea sets the tone for the rest of her book which goes into depth about developmental novelties and their relation to evolution. Heterotopy is a somewhat obscure but well demonstrated example of how developmental change can lead to novel forms. The central concept is that a feature seen in one area of an organism has had its location changed in evolutionary lineages.

Heterotopy in molecular biology

Heterotopy in molecular biology is the name given to the expression or placement of a gene product from what is typically found in one area to another area. It can also be further expanded to a subtle form of

exaptation Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common ...

where a gene product used for one underlying purpose in a diverse group of organisms can re-emerge repeatedly to produce seemingly

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

distributions of traits. But actual phylogenetic analysis supports a monophyletic model as does evolutionary theory. Heterotopy is used to explain this and there are so commonly cited examples. An example is

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

a very durable structural protein used in surgical sutures as well as durable

varnishes Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in various ...

but is common to many animals especially

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

and

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

. But is also found in the

African clawed frog The African clawed frog (''Xenopus laevis'', also known as the xenopus, African clawed toad, African claw-toed frog or the ''platanna'') is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws ...

(''Xenopus laevis''). Wagner et al., suggest that chitin might have a microscopic function observed in cell to cell signaling and the manufacture of insect cuticle for example might represent a recurrent change in the location of expression

Speculative, but however Chitin synthase is maintained in many lineages where it does not have an obvious macroscopic function.Wray and McClay 1989 It is thought that because so many organisms share such a profound degree of genetic and molecular similarity that shifts in the location of expression might be a regular occurrence throughout time. Molecular analysis shows that proteins that seem to have a single specific function are instead found in many different tissue types. One example of this phenomenon is crystallin, a clear protein that makes up the lens of the eye; it is also has structural functions in the heart.

References

{{DEFAULTSORT:Heterotopia (Medicine) Congenital disorders

Examples

Heterotopy in molecular biology

See also

References