Identification of GABABR2 in Rat Testis and Sperm

Abstract

Abstract. GABA is capable of mimicking and potentiating the action of progesterone in initiating the acrosome reaction (AR) of mammalian sperm. The GABA-initiated AR is mediated by GABA AR; whereas GABABR1 protein found in rat testis and sperm tends to modify this process. Moreover, the occurrence of GABABR2, a subunit essential for the formation of a functionally active GABABR, in rat testis and sperm has not been established. In the present study, rat testis and sperm were analyzed for the presence of GABABR2 transcript and protein by RT-PCR, Northern blot, Western blot and an indirect immunofluorescence technique. Northern blot shows that the transcript of testis GABABR2 is shorter (~3.0 Kb) than that of the brain (~5.6 Kb). The full length testis GABABR2 cDNA was prepared by RACE-PCR and found to be shorter by 2.2 Kb in the segment at the extreme terminus of 3'UTR of rat brain GABABR2 but, the sequences corresponding to the open reading frame and 5'-UTR of rat testis GABABR2 were found to be identical to those of rat brain. GABABR2 protein isolated from rat epididymal sperm was slighter larger than those of rat testis and brain. It was principally localized in the acrosome region of the head of rat sperm by an indirect immunofluorescence technique. The present results establish that GABABR2 protein is produced in rat testis and sperm and may play a role in GABA triggering of AR. Key words: GABABR2, Testis, Sperm (J. Reprod. Dev. 49: [397][398][399][400][401][402] 2003) -Aminobutyric acid (G ABA) is t he mos t abundant inhibitory neurotransmitter in the vertebrate central nervous system (CNS). Its effects are mediated through two ligand-gated channels ( G A B A A a n d G A B A C r e c e p t o r s ) , a n d a m e t a bo t r o pi c G p ro te in -c o up led r e ce pt o r , GABABR. This species of the receptor acts through G proteins by regulating potassium and calcium channels [1]. The first GABAB receptor cDNA (termed GABABR1) was isolated first from rat brain with a high affinity radio-ligand [2]. After the cloning the GABA B R1, another subunit of GABA B receptor, GABA B R2, was identified [3][4][5]. Several l i n e s o f e v i d e n c e d e m o n s tr a t e d th a t t h e heterodimerization of GABABR1 and GABABR2 is a requirement for the formation of a functional GABAB receptor [3][4][5][6]. GABABR1 and GABABR2 form a heterodimer by a linkage involving the interaction at the C-terminal tails [6].A GABAergic system also occurs in several peripheral tissues [7] e.g. GABAA receptor is expressed in human sperm [8,9]. It is interesting to note that rat oviduct contains more than twice the amount of GABA than the brain [10]. Moreover, GABA A receptor mediates progesterone-induced acrosome reaction (AR), an exocytotic event

GABA_B1 Knockout Mice Reveal Alterations in Prolactin Levels, Gonadotropic Axis, and Reproductive Function

“…Testes express the GABA biosynthetic enzyme GAD [28, 41], GABA A and GABA B receptors [28, 42, 43,] as well as GABA transporters [28, 44]. Furthermore, a physiological role for GABA in the control of Leydig cell proliferation and steroid synthesis has been proposed [28, 45].…”

Identification of GABA receptors in chick retinal pigment epithelium

“…For example, GABA A receptors have been shown to be located in murine gut [21], in cat carotid body [22], in rat taste bud [23], in human thyroid [24], human hepatocellular [25], human peripheral blood mononuclear cells [26], and human prostate [27]. GABA B receptors have been reported in spider leg mechanosensilla [28], rat testis and sperm [29], the rat olfactory bulb [30], the rat taste bud [23], the rat gastrointestinal tract [31], and rat cardiomyocytes [32]. In human, GABA B receptors are reported in airway epithelium [33] and fallopian tube [34], and GABA C receptors have been reported in gut [35], testis and spermatozoa [36].…”

Suppression of Progesterone-enhanced Hyperactivation in Hamster Spermatozoa by γ-aminobutyric Acid

“…Moreover, the increased hyperactivation of rat sperm by P is inhibited by a GABA A receptor antagonist [19]. Although the GABA B receptor also exists in rat spermatozoa and is localized in the sperm head [23,24,25], it is unclear whether the GABA B receptor is involved in regulation of hyperactivation.…”