Secretagogin in the Central Nervous System of the Gecko, Hemidactylus leschenaultii

Secretagogin (scgn), a novel calcium‐binding protein (CBP), regulates Ca 2+ homeostasis in neurons, controls exocytosis, and serves as a Ca 2+ ‐sensor. Scgn is widely expressed in the mammalian brain and has emerged as a novel neuroendocrine regulator. Although scgn is considered as a phylogenetically conserved CBP, little is known about its significance in the brain of nonmammalian vertebrates. Herein, we characterized the scgn‐encoding cDNA and mapped scgn‐equipped elements in the brain and spinal cord of a gecko, Hemidactylus leschenaultii ( hl ). In the brain, a 1303‐bp hlscgn transcript containing 822‐bp cds and 481‐bp 3′ untranslated region (UTR) was identified. The hlscgn transcript predicted to encode a hexa EF‐hand 273‐aa hlscgn showed 70%–90% similarity with scgn from other vertebrates. The EF2‐motif in hlscgn showed highest Ca 2+ ‐binding affinity as compared to that in scgn from other vertebrates. The anti‐scgn antiserum detected a ∼32‐kDa band in the brain, and cell bodies/fibers in the cortex, dorsal ventricular ridge, amygdalae, striatum/septum, hypothalamic/thalamic nuclei, substantia nigra, interpeduncular, solitary tract, and raphe nuclei, and spinal cord. The scgn neurons in the paraventricular (PVN) and supraoptic nuclei co‐expressed either thyrotropin‐releasing hormone or vasotocin, but not mesotocin. As insulin regulates the activity of PVN neurons in mammals, and scgn expression in the mammalian/teleost brains, the superfused hypothalamic slices of H. leschenaultii were treated with insulin, and the changes in scgn‐ir/ hlscgn ‐mRNA in PVN were analyzed. Compared to control, insulin treatment significantly increased scgn expression. Thus, scgn seems to be a highly conserved protein in the vertebrate hierarchy with a variety of attributes, inclusive of neuroanatomy, neuroendocrine control, and regulation by insulin.