Comparative expression patterns of Sox2 and Sox19 genes in the forebrain of developing and adult turbot (Scophthalmus maximus)

Abstract

The turbot, Scophthalmus maximus, belongs to the flatfishes (order Pleuronectiformes), which display substantial asymmetry of the olfactory organs and forebrain. Sox genes code for SRY-related HMG domain-bearing transcription factors involved in various developmental processes. Group B1 Sox genes as Sox2 and Sox19 appear to play major roles in neural development. Here, we characterized by in situ hybridization the developmental expression of Sox2 and Sox19 genes in metamorphic and postmetamorphic specimens and young adults of both sexes. Expression of S. maximus Sox2 (Sm-Sox2) and Sm-Sox19 mRNAs was detected in ependymal cells of different regions of the telencephalon, preoptic region, hypothalamus, and thalamus at all stages investigated. Sm-Sox2 expression but not Sm-Sox19 occurred in neurons located in particular regions such as the dorsal nucleus of the ventral telencephalon, the medial zone of the dorsal telencephalon, preoptic area and hypothalamus. Although Sm-Sox2 and Sm-Sox19 are expressed differentially in gonads, no sex differences in their expression were observed between male and female forebrains. We also investigated the topographical relation between Sox expression and cell proliferation using series double immunostained for a radial glial marker (BLBP) and cell proliferation marker (PCNA). Sm-Sox2 and Sm-Sox19 were strongly expressed in ependymal cells located in neurogenic niches revealed by the BLBP and PCNA immunostaining. Comparison with other teleosts indicates similar expression of Sox2 and Sox19 in the telencephalon, supporting conserved roles for both genes in teleost brains.

Organization of radial glia reveals growth pattern in the telencephalon of a percomorph fish Astatotilapia burtoni

“…To investigate locations of cell proliferation and differentiation in the telencephalon, we stained transverse sections with the proliferation marker PCNA, the transcription factor Sox2 expressed in stem cells and fish glial cells (Taboada et al, 2018), and doublecortin (DCX), a marker for neurogenesis and neuronal differentiation (Couillard‐Despres et al, 2005). PCNA stainings clearly confirmed proliferating cells in the outer surface layer of the telencephalon where the cell bodies of radial glia cells are located.…”

“…To investigate locations of cell proliferation and differentiation in the telencephalon, we stained transverse sections with the proliferation marker PCNA, the transcription factor Sox2 expressed in stem cells and fish glial cells (Taboada et al, 2018) restricted to the ventricular surface layer, nor did they all appear to be glial cells.…”