Secretagogin in the brain and pituitary of the catfish, Clarias batrachus: Molecular characterization and regulation by insulin

Abstract

Secretagogin (scgn), is a novel hexa EF-hand, phylogenetically conserved calciumbinding protein. It serves as Ca 2+ sensor and participates in Ca 2+ -signaling and neuroendocrine regulation in mammals. However, its relevance in the brain of nonmammalian vertebrates has largely remained unexplored. To address this issue, we studied the cDNA encoding scgn, scgn mRNA expression, and distribution of scgnequipped elements in the brain and pituitary of a teleost, Clarias batrachus (cb). The cbscgn cDNA consists of three transcripts (T) variants: T1 (2185 bp), T2 (2151 bp) and T3 (2060 bp). While 816 bp ORF in T1 and T2 encodes highly conserved six EF-hand 272 aa protein fully capable of Ca 2+ -binding, 726-bp ORF in T3 encodes 242 aa protein.The T1 showed >90% and >70% identity with scgn of catfishes, and other teleosts and mammals, respectively. The T1-mRNA was widely expressed in the brain and pituitary, while the expression of T3 was restricted to the telencephalon. Application of the antiscgn antiserum revealed a ∼32 kDa scgn-immunoreactive (scgn-i) band (known molecular weight of scgn) in the forebrain tissue, and immunohistochemically labeled neurons in the olfactory epithelium and bulb, telencephalon, preoptic area, hypothalamus, thalamus, and hindbrain. In the pituitary, scgn-i cells were seen in the pars distalis and intermedia. Insulin is reported to regulate scgn mRNA in the mammalian hippocampus, and feeding-related neuropeptides in the telencephalon of teleost. Intracranial injection of insulin significantly increased T1-mRNA expression and scgn-immunoreactivity

Immunohistochemical distribution of secretagogin in the mouse brain

“…Secretagogin expression is abundant in areas like the olfactory bulb and the hippocampus not only in rodents, but also in other mammals, such as humans ( Attems et al, 2012 ; Tapia-González et al, 2020 ), red foxes ( Ortiz-Leal et al, 2023 ), and even in chickens ( Gáti et al, 2014 ) and catfishes ( Basu et al, 2022 ). Knowing that the olfactory bulbs are part of the archicortex (the most primitive domain of the cerebral cortex), and that the hippocampus is included in the paleocortex, the next oldest cortical region, SCGN could have appeared in the brain early in evolution and could remain present in these cortical areas but not in more recent ones, where other calcium-binding proteins are abundant.…”

“…Since its discovery, SCGN has been widely studied in the brain of different species. Some studies show SCGN distribution in the whole brain, for example in fishes ( Basu et al, 2022 ), birds ( Gáti et al, 2014 ) or rats ( Maj et al, 2012 ), but most of them focus on a specific brain area. In addition to the studies mentioned above, SCGN expression has been analyzed in different species in the amygdala, ( Mulder et al, 2010 ; Gyengesi et al, 2013 ; Hevesi et al, 2021 ), the olfactory bulb ( Mulder et al, 2009 ; Kosaka and Kosaka, 2013 ; Ortiz-Leal et al, 2023 ), or the hippocampus ( Attems et al, 2007 ; Tapia-González et al, 2020 ), among others.…”