The name of the SCO comes from its location beneath the posterior commissure, a bundle of nerve fibers interconnecting parts of the two hemispheres of the brain.

[1] Functions of the SCO are unknown; some evidence indicates it may participate in clearance of certain compounds from the cerebrospinal fluid, and possibly in morphogenetic mechanisms, such as development of the posterior commissure.

[3] Ependymal cells secrete high molecular mass glycoproteins into the cerebrospinal fluid, in which the bulk of them condense to form a filamentous structure named Reissner's fiber.

[4] The subcommissural organ/Reissner's fiber complex is thought to be involved in the reabsorption and circulation of the cerebrospinal fluid, and with functions related to electrolyte and water balance.

This multidomain organization is a special feature of the Chordate Phylum, and there is a high degree of conservation in the amino acids composition in mammals.

The putative function of SCO-spondin in neuronal differentiation is discussed regarding these features and homologies with other developmental molecules of the central nervous system exhibiting TSR domains, and involved in axonal guidance.

Therefore, it is a candidate to interfere with neuronal development and/or axonal guidance during ontogenesis of the central nervous system in the modulation of side-to-side and side-to-substratum interactions, and also in promoting neurite outgrowth.

Similar types of arrangement was encountered in zonadhesins and immunoglobulin G (IgG) FC binding fragment which may account for SCO-spondin functional aspect on promoting cell-to-substratum adhesivity.

Nevertheless, SCO-spondin is also present during the adult life, and similarly to thrombospondins, which act on various biological systems, i.e., neuronal differentiation, angiogenesis and platelet aggregation.

It is the first secretory structure to differentiate and remains fully developed and functional during the life of almost every vertebrate, excluding bats, anthropoid apes and humans.

Following this maxed developed state, the SCO starts regressing and in children from 3 to 4 years old it already has a vestigial character, being reduced to islet like structures on the adult.

[20] As part of the embryonic cerebrospinal fluid (eCSF), SCO-spondin is of the uttermost importance in the development of the neuronal system, being a key protein in the balancing of differentiation and proliferation of the neuroepithelium.

It starts being secreted by the diencephalic floor plate in the first embryonic stages playing an important part in the development and differentiation of structures such as the pineal gland.

[22] In addition to the functions in axon guidance and related growth of the posterior commissure, the SCO-spondin also appears to have a role on the adhesion of the trophoblast to the uterine walls.

[24][25] It is suggested that this is related to immunological blockage of SCO secretions and Sylvian's aqueduct malformation[26] and obliteration or turbulent cerebrospinal fluid flow due to the absence of Reissner's fibers.

[30][31] In 1860, Ernst Reissner, anatomist at the University of Dorpat, published a monograph on the microscopic structure of the spinal cord of Petromyzon fluviatilis.

He described a string of 1.5 μm in diameter characterized by its high refringence, its extremely regular shape, and its lying free within the central canal.