Glial domains and nerve fiber patterns in the fish retinotectal pathway

Abstract

Optic nerve fibers run parallel from the retina as far as the optic tract in fish, then suddenly criss-cross into a new pattern matching the tectal map. This change coincides with a unique demarcation between two astroglial territories in the retinotectal pathway, located where the optic chiasm occurs in other vertebrates, which we defined using antibodies directed against intermediate filaments (IF). We found that astroglia in optic nerve territory express an Mr 56,000 IF polypeptide, band 3, which we identify as the fish equivalent of vimentin in mammals. These astrocytic cells lack glial fibrillary acidic protein (GFAP; cf. Dahl and Bignami, 1973). Conversely, glia in brain territory, that is, in the optic tract and elsewhere in the CNS, lack the fish vimentin, but express GFAP. By electron microscopy, we obtained evidence that new retinal axons extend swiftly through the growing optic nerve, where they are tightly shepherded into a narrow track by newly differentiating glial cells, positive for the fish vimentin. In the GFAP-positive glial territory of the optic tract, by contrast, growing axons are slowed down and probably branch. We suggest that this allows them to fasciculate accurately with older fibers and thereby propagate a tectotopic pattern established by pioneer axons in the embryo.

Similarities and differences between fish oligodendrocytes and schwann cells in vitro

“…Oligodendrocytes derived from a recently divided oligodendrocyte either do not necessarily go through a phase in which they transiently express GFAP, or the duration of their transient GFAP expression is very brief. While A2B5 did not define a specific differentiation state ofglial cells considered here, a precursor for oligodendrocytes reminiscent of the A2B5-positive progenitor of mammals (Raff et al, 1983) appears to exist in fish larvae (Jeserich and Stratmann, 1992) and mature brain tissue, too (Maggs and Scholes, 1986;Jeserich, unpublished). They are obviously needed, since new retinal axons are continuously added in adult fish optic nerves (Easter et al, 1981) which have to become myelinated as they mature.…”

Reticular astrocytes in the fish optic nerve: macroglia with epithelial characteristics form an axially repeated lacework pattern, to which nodes of Ranvier are apposed

“…Astrocytes in the optic nerves of amphibia and fish are uniquely specialized, forming a glial territory demarcated from the rest of the CNS by sharp boundaries at the optic nerve head and the optic chiasm (Maggs and Scholes, 1986;Nona et al, 1989). They are exceptional in lacking the astrocyte cytoskeletal marker glial fibrillary acidic protein (GFAP; Dahl and Bignami, 1973;Quitschke et al, 1985;Dahl et al, 1986) and they express instead abundant cytokeratin-type intermediate filaments (IFS), as recently determined immunocytochemically (Mark1 and Franke, 1988;Rungger-Brandle et al, 1989) and from the DNA sequence of the goldfish ON3 glial IF gene (Giordano et al, 1989).…”

Identification of astrocyte- and oligodendrocyte-like cells of goldfish optic nerves in culture

“…Multipolar cells in 5-day-old cultures were anti-G-GFAP but rarely O~ positive. In 5-week-old cultures, however, roughly 75% of the multipolar cells were double-labeled with both anti-G-GFAP and O1; 10% were single labeled with Mab O~ and 15% with anti-G-GFAP, respectively.Since goldfish retinal axons regenerate readily after injury it has been supposed that the glial cells of the fish optic nerve possess growth-promoting properties [5, 8]. Compared to mammals very little is known about glial cells in fish, one reason being that it has been difficult to identify fish astrocytes by immunohistochemistry [3,5].…”

“…Since goldfish retinal axons regenerate readily after injury it has been supposed that the glial cells of the fish optic nerve possess growth-promoting properties [5, 8]. Compared to mammals very little is known about glial cells in fish, one reason being that it has been difficult to identify fish astrocytes by immunohistochemistry [3,5].…”

“…Compared to mammals very little is known about glial cells in fish, one reason being that it has been difficult to identify fish astrocytes by immunohistochemistry [3,5]. To test the interaction of regenerating axons with glial cells in vitro requires that glial cells can be raised and identified in culture.…”