Distribution of the transcription factor islet‐1 in the central nervous system of nonteleost actinopterygian fish: Relationship with cholinergic and catecholaminergic systems

Abstract

Islet-1 (Isl1) is one of the most conserved transcription factors in the evolution of vertebrates, due to its continuing involvement in such important functions as the differentiation of motoneurons, among other essential roles in cell fate in the forebrain.Although its functions are thought to be similar in all vertebrates, the knowledge about the conservation of its expression pattern in the central nervous system goes as far as teleosts, leaving the basal groups of actinopterygian fishes overlooked, despite their important phylogenetic position. In order to assess the extent of its conservation among vertebrates, we studied its expression pattern in the central nervous system of selected nonteleost actinopterygian fishes. By means of immunohistochemical techniques, we analyzed the Isl1 expression in the brain, spinal cord, and sensory ganglia of the cranial nerves of young adult specimens of the cladistian species Polypterus senegalus and Erpetoichthys calabaricus, the chondrostean Acipenser ruthenus, and the holostean Lepisosteus oculatus. We also detected the presence of the transcription factor Orthopedia and the enzymes tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) to better locate all the immunoreactive structures in the different brain areas and to reveal the possible coexpression with Isl1. Numerous conserved fea-

Expression of the transcription factor Isl1 in dopaminergic neurons of the mouse forebrain

“…The SCN is, however, part of the paraventricular area in the mouse, where Isl1 is absent in all species. In addition to work done in tetrapods, mapping of Isl1 expression in the zebrafish and non-teleost actinopterygian fishes reveal a similar pattern of Isl1 distribution in the forebrain (Schredelseker and Driever, 2020; López et al, 2021; Lozano et al, 2023). Thus, Isl1 expression is conserved in vertebrates and characterises the anteriormost part of the forebrain, from the ventral telencephalon and hypothalamus to the diencephalic prosomere 3.…”

“…In the forebrain, the expression of Isl1 has been extensively characterised in model vertebrates like the frog, Xenopus laevis (Moreno et al, 2008; Domínguez et al, 2013, 2014, 2015) and the zebrafish, Danio rerio (Schredelseker and Driever, 2020; López et al, 2021; Lozano et al, 2023), but a systematic description of Isl1 expression in the mouse forebrain is lacking. Here, we study the distribution of Isl1 in the hypothalamus and neighbouring areas (preoptic area and prethalamus) in the mouse and find a high degree of colocalisation of Isl1 protein in dopaminergic neuronal populations during development and adulthood.…”

Distribution of gamma‐aminobutyric acid immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with other fishes

“…For describing the regionalization of the sturgeon forebrain, we adopted the prosomeric model (López et al., 2022; Lozano et al., 2023; Puelles, 2019; Puelles & Rubenstein, 2003, 2015), and divisions of the sturgeon hypothalamus followed as far as possible those of Santos‐Durán et al. (2022) in sharks.…”

“…Following the prosomeric model (López et al., 2022; Lozano et al., 2023; Puelles, 2019; Puelles & Rubenstein, 2003, 2015), the diencephalon is comprised of the derivatives of three diencephalic prosomeres (p1–p3, numbered from caudal to rostral), each consisting of alar and basal regions.…”

“…For describing the regionalization of the sturgeon forebrain, we adopted the prosomeric model (López et al, 2022;Lozano et al, 2023;Puelles, 2019;Puelles & Rubenstein, 2003, and divisions of the sturgeon hypothalamus followed as far as possible those of Santos-Durán et al (2022) in sharks. The description of immunoreactive structures was done topographically with respect to the anteriorposterior, dorsoventral, and mediolateral axes of the head.…”