Sexually Dimorphic Expression of Glutamate Decarboxylase mRNA in the Hypothalamus of the Deep Sea Armed Grenadier, <i>Coryphaenoides (Nematonurus) armatus</i>

Abstract

Glutamate decarboxylase (GAD), is a key enzyme in the central nervous system (CNS) that synthesizes the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) from glutamate. Our previous phylogenetic studies on the evolution of this enzyme indicates that there are at least two distinct forms: GAD65 and GAD67. They are the products of separate genes and probably derive from a common ancestral GAD gene following gene duplication prior to the emergence of the teleosts more than 200 Myr ago. Furthermore, a third GAD-like molecule, GAD3, discovered in the armed grenadier, Coryphaenoides (Nematonurus) armatus, is equally divergent from both GAD65 and GAD67. Specimens of C. (N.) armatus were collected by trawl at a depth of 4,000 m in the Porcupine Seabight (Northeastern Atlantic), and brains dissected and frozen for RNA extraction. All three GAD forms are found in the cerebellum, telencephalon and hypothalamus. Semiquantitative PCR analysis showed that males and females have similar levels of expression of GAD67 and GAD3 in the tissues studied. Independent of the sex examined, the levels of expression of GAD65 and GAD67 in the cerebellum were approximately half that in the telencephalon. GAD3 levels were approximately 30% higher in the cerebellum than in either the telencephalon or hypothalamus. In contrast to GAD67 and GAD3, hypothalamic expression of GAD65 mRNA is 1.8 times higher (p < 0.05) in males than in females. These data indicate that the expression of GAD65, a key enzyme for the synthesis of GABA is sexually dimorphic in females and males of C. (N.) armatus.

The Spatial Relationship of γ-Aminobutyric Acid (GABA) Neurons and Gonadotropin-Releasing Hormone (GnRH) Neurons in Larval and Adult Sea Lamprey, <i>Petromyzon marinus</i>

“…The authors concluded that GAD mRNA are translated efficiently into enzymatically active GAD which produces GABA, and that the pattern of GAD expression is consistent with the notion that GAD and its product, GABA, play a signaling role during development. In another study, utilizing the polymerase chain reaction, it was shown that the hypothalamic expression of GAD 65 was significantly greater in the male deep sea armed grenadier (Coryphaenoides (Nematonurus) armatus) than in the female indicating that the synthesis of GABA is sexually dimorphic in this species [Trudeau et al, 2000b]. In the present study we demonstrated, by in situ hybridization, that in larval lamprey, both GABA and GAD were present in the same population of cells.…”

Three Distinct Glutamate Decarboxylase Genes in Vertebrates

“…In the deep-sea fish in which gad3 was first described, the armed grenadier, Coryphaenoides (Nematonurus ) armatus, gad2 mRNA levels were found to be expressed in the brain in a sexually dimorphic manner, i.e. higher in male hypothalamus than in female, but no differences were found in gad3 levels 35 . In the goldfish, however, gad3 mRNA levels in the telencephalon were highest in sexually mature fish of both sexes during the breeding period 55 .…”

“…Transcript DNA sequences for elephant shark were retrieved from the elephant shark Ensembl server. Transcript cDNA sequences for grenadier were retrieved from NCBI 15 35 . The spotted gar genome shares extensive similarity with both tetrapod and teleost genomes, so we chose to focus on this species for sequence alignment, phylogenetics, and intron/exon structure comparisons 30 .…”

Physiological role of genes involved in taurine biosynthesis in fishes and in silico approach to determine transcription factors in their promoters’ zone

“…It is known that there are three different isoforms of the gene in vertebrates (Grone & Maruska 2016). In fishes, some studies have been directed at the deep sea armed grenadier Coryphaenoides (Nematonurus) armatus (Trudeau et al 2000), goldfish (Lariviere et al 2002), zebrafish (Mueller & Guo 2009), and detected by RNAseq in gulf pipefish Syngnathus scovelli (Beal et al 2018). Hence, in zebrafish, Cocco et al (2017) studied gad localization in different brain regions and found three different paralogs, of which two resemble the gad1 paralog of mammals and the third one the gad2.…”