Abstract
In the brain of teleost fish, radial glial cells are the major type of astroglial cells. To answer the question as to how radial glia structures adapt to the continuous growth of the brain, which is characteristic of salmonids, it is necessary to study various types of cells (neuronal precursors, astroglial cells, and cells in a state of neuronal differentiation) in the major integrative centers of the salmon brain (telencephalon and tectum opticum), using rainbow trout, Oncorhynchus mykiss, as a model. A study of the distribution of several molecular markers in the telencephalon and tectum with the identification of neural stem/progenitor cells, neuroblasts, and radial glia was carried out on juvenile (three-year-old) O. mykiss. The presence of all of these cell types provides specific conditions for the adult neurogenesis processes in the trout telencephalon and tectum. The distribution of glutamine synthetase, a molecular marker of neural stem cells, in the trout telencephalon revealed a large population of radial glia (RG) corresponding to adult-type neural stem cells (NSCs). RG dominated the pallial region of the telencephalon, while, in the subpallial region, RG was found in the lateral and ventral zones. In the optic tectum, RG fibers were widespread and localized both in the marginal layer and in the periventricular gray layer. Doublecortin (DC) immunolabeling revealed a large population of neuroblasts formed in the postembryonic period, which is indicative of intense adult neurogenesis in the trout brain. The pallial and subpallial regions of the telencephalon contained numerous DC+ cells and their clusters. In the tectum, DC+ cells were found not only in the stratum griseum periventriculare (SGP) and longitudinal torus (TL) containing proliferating cells, but also in the layers containing differentiated neurons: the central gray layer, the periventricular gray and white layers, and the superficial white layer. A study of the localization patterns of vimentin and nestin in the trout telencephalon and tectum showed the presence of neuroepithelial neural stem cells (eNSCs) and ependymoglial cells in the periventricular matrix zones of the brain. The presence of vimentin and nestin in the functionally heterogeneous cell types of adult trout indicates new functional properties of these proteins and their heterogeneous involvement in intracellular motility and adult neurogenesis. Investigation into the later stages of neuronal development in various regions of the fish brain can substantially elucidate the major mechanisms of adult neurogenesis, but it can also contribute to understanding the patterns of formation of certain brain regions and the involvement of RG in the construction of the definite brain structure.
Highlights
Studies of adult animal neurogenesis are an important area of developmental neurobiology [1]
Another type of glutamine synthetase (GS) positive (GS+) cell was represented by radial glia (RG); the bodies of the RG cells were located in the periventricular zone (PVZ), and their long processes penetrated into the subventricular zone (SVZ) and deep into the parenchymal layers of the telencephalon (Figure 1A, red inset; and Table 1)
The presence of varicose glutamatergic fibers in the trout tectum may be associated with the differentiation of precursors into glial cells
Summary
Studies of adult animal neurogenesis are an important area of developmental neurobiology [1] The interest in these studies is explained by the necessity to identify different types of cells with stem properties in the adult animal brain for the further assessment 4.0/). To answer the question as to how the radial glia structures adapt to the continuous growth of the brain characteristic of salmon fish, it is necessary to study various types of cells (neuronal precursors, astroglial cells, and cells in a state of neuronal differentiation) in the main integrative centers of the brain: telencephalon, tectum opticum, cerebellum and brainstem of rainbow trout, and Oncorhynchus mykiss. Various aspects of constitutive neurogenesis, such as environmental exposure [9], the influence of circadian rhythms [10], and sexual dimorphism [11], have been investigated
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