In small ruminants, such as goats and sheep, a primer pheromone produced by males induces an out‐of‐seasonal ovulation in anoestrous females, a phenomenon known as the male effect. The male effect is unique in that an external chemical stimulus can immediately modulate the activity of the hypothalamic gonadotrophin‐releasing hormone (GnRH) pulse generator. We have established a monitoring method of the GnRH pulse generator activity in Shiba goat. Using this method as a sensitive bioassay to assess the male effect pheromone activity, we have shown that the male effect pheromone is synthesised in an androgen‐dependent manner in the sebaceous glands or their vicinity in specific body regions in goats. Although chemical identity of the pheromone is yet to be determined, analyses of male goat hair extracts by gas chromatography fractionation suggest that the male effect pheromone is a volatile substance with relatively small molecular weight. From morphological and molecular biological studies in goats, it is suggested that the pheromone molecule is detected by a member of the V1R family located on both the olfactory neurones and the vomeronasal sensory neurones, and the pheromone signal is conveyed to the medial nucleus of amygdala via the main olfactory and vomeronasal pathways and, subsequently, to the hypothalamic GnRH pulse generator to enhance its activity.
The male effect is a well-known phenomenon in female sheep and goats whereby a pheromone-induced activation of reproductive function occurs. However, the molecule(s) involved in this phenomenon are unknown. We investigated gene expression profiles for the induction of male effect pheromone synthesis using a PCR-based cDNA subtraction strategy. We constructed two subtracted cDNA libraries using mRNA from the skin of the head or rump region of orchidectomized male goats with or without pheromone induction using testosterone or dihydrotestosterone (DHT). Both libraries were assumed to contain genes whose expression increases with pheromone induction. Clones (n = 480) from each library were sequenced and identified using BLAST to reveal 115 and 239 types of sequences in the libraries of the head and rump region, respectively. Among these, 12 genes were expressed in both libraries. We conducted real-time PCR to further analyze their expression using cDNA samples derived from pheromone-producing or nonproducing skin from the head of an ovariectomized female goat with or without DHT implantation, respectively. For nine genes, we observed significantly increased expression in samples following DHT implantation. Among these, stearoyl-CoA desaturase 1 (SCD1) and elongation of long chain fatty acids family member 5 (ELOVL5) genes showed more than 100-fold higher expression levels in pheromone-positive samples, suggesting that the products of these genes may be important in pheromone synthesis.
Abstract. The 'male effect' is a well-known phenomenon in female sheep and goats, whereby pheromone-induced activation of reproductive function occurs. In a previous study, we showed that the genes for elongation of long-chain fatty acids family member 5 (ELOVL5) and stearoyl-CoA desaturase 1 (SCD1) increased their expression significantly, concomitant with induction of pheromone synthesis. Therefore, these genes were considered to be prime candidate genes for pheromone synthesis. In the present study, we performed in situ hybridization to investigate where these two genes are expressed in goat skin. Strong positive signals were detected for both genes in the head skin of the male goat, which is the main site of pheromone production, and were mainly in the basal layer of the sebaceous gland cells, with the remaining cells showing negligible signals. None of the cells in the rump skin of the male goat or the head skin of the orchidectomized goat, neither of which produce pheromone, exhibited strong positive signals. The present study demonstrates that expression of these two candidate genes for pheromone synthesis is primarily localized in the sebaceous glands of the pheromone-producing skin region. , the 'male effect' is well known as a pheromone-induced phenomenon in which seasonally anovulatory females resume ovarian cyclicity in response to introduction of a male. In goats, we have previously shown that the 'male effect' pheromone is produced in a testosterone (T)-dependent manner in the skin of the head region, but not in the skin of the rump region [4,5], using a bioassay for pheromone activity that we had developed previously [6,7]. Dihydrotestosterone (DHT) treatment induces pheromone production in the skin of the rump region, where pheromones are not produced constitutively [8]. Interestingly, 'male effect' pheromone activity is also induced in female skin by androgens [9]. We found that expression of the genes for elongation of long-chain fatty acids family member 5 (ELOVL5) and stearoyl-CoA desaturase 1 (SCD1) increased significantly, concomitant with induction of pheromone synthesis, in three types of skin models, i.e., the head skin of Ttreated orchidectomized (ODX) male goats, rump skin of DHT-treated ODX male goats and head skin of DHT-treated ovariectomized female goats, thereby implicating these two genes as prime can-
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