Androgen feedback effects on LH and FSH, and photoperiodic control of reproduction in male three-spined sticklebacks, Gasterosteus aculeatus

Abstract

, M. et al. (2013) "Androgen feedback effects on LH and FSH, and photoperiodic control of reproduction in male three-spined sticklebacks, Gasterosteus aculeatus" General and Comparative Endocrinology, Access to the published version may require subscription. Sexual maturation in the stickleback is controlled by photoperiod. The aim of this study was to find out whether changes in feedback effects exerted by sex steroids could mediate the photoperiodic effect, which is regarded to be of an all-or-nothing character. To that end, males were castrated and treated with different doses of testosterone (T) and in one experiment also with the aromatase inhibitor fadrozole (AI) and kept under different photoperiods. In control fish, long day (LD 16:8) stimulated maturation, associated with more hypertrophied kidneys (a secondary sexual character) and higher levels of pituitary lhb and fshb mRNA than under short day conditions (LD 8:16). Under LD 8:16, low doses of T suppressed both lhb and fshb mRNA levels. However, with the use of high doses of T and/or longer photoperiods the inhibitory effects on lhb and fshb mRNA levels became less clear or instead positive effects were observed. Under intermediate photoperiod conditions, the negative feedback effect of a low dose of T on fshb was more prominent with shorter photoperiods, whereas no such shift was observed for lhb mRNA. The inhibitory effect of the low dose of T on lhb mRNA levels under LD 8:16 was abolished by AI, whereas the stimulatory effect of the high dose of T was not. The negative feedback effects were more marked under short days than under long days, whereas positive feedback effects were more marked under long days. The suppression of both fshb and lhb mRNA levels by low androgen levels, especially under short days, may inhibit maturation completely unless a rise of androgens above threshold levels would allow complete maturation. 1.IntroductionIn order to reproduce at the optimal time of the year, organisms use endogenous cycles and environmental cues, the most important of which being the photoperiod [18]. In vertebrates, the circulating levels of the pituitary gonadotropic hormones (GtHs), LH and FSH, are higher under stimulatory than under non-stimulatory photoperiods, resulting in increased gonadal acitivity. The pituitary is under control from the brain, especially the hypothalamus, and by gonadal hormones which exert feedback effects on the brain-pituitary-gonad (BPG) axis. In mammals and birds, several studies have shown changes in steroid feedback effects on the BPG axis by photoperiod, but also gonad-independent effects, i.e. higher circulating GTH levels in castrated animals kept under a stimulatory photoperiod are known [16]. This has been studied very little in poikilothermic vertebrates.Photoperiod is an important factor in synchronizing reproduction also in fishes, including the three-spined stickleback which is perhaps the fish where the mechanisms of photoperiodic effects have been studied most extensively [2,3,7,8,9]. At sexual maturat...

Androgens Increase lws Opsin Expression and Red Sensitivity in Male Three-Spined Sticklebacks

“…Both traits were suppressed by castration and stimulated by 11 KA, also consistent with previous reports [41], [42]. Levels of lws mRNA were higher in sexually mature than in immature male and female sticklebacks.…”

Diversity in reproductive seasonality in the three-spined stickleback,Gasterosteus aculeatus

“…However, expression of both gonadotropic hormones was very low in the period when spermatogenesis commenced in June. The seasonal pattern of gonadotropic hormones may be induced by photoperiodic changes, because male sticklebacks have higher levels of mRNA for both LHβ and FSHβ under a long-day condition (16 h light:8 h dark) than those kept under a short-day condition (8 h light:16 h dark) (Shao et al, 2013). The expression of gonadotropins changes not only seasonally but also depending on the nesting cycle of the stickleback.…”

“…Recent genetic and genomic studies have revealed the molecular mechanisms underlying the morphological, physiological and behavioural divergence between anadromous and freshwater populations of three-spined stickleback (Chan et al, 2010;Greenwood et al, 2013;Indjeian et al, 2016;Marques et al, 2017;Miller et al, 2007;O'Brown et al, 2015;Xie et al, 2019). Third, as discussed in detail below, the endocrine mechanisms underlying seasonal reproduction have been investigated in the three-spined stickleback (Hellqvist et al, 2006;Shao et al, 2013Shao et al, , 2015Sokołowska et al, 2004).…”

Microinjection for Transgenesis and Genome Editing in Threespine Sticklebacks

“…A number of genomic regions underlying morphological changes have been identified with promising candidate genes, but these candidates have not yet been functionally tested 9–12 . In addition, sticklebacks are common models for studies of population genetics/genomics 13,14 , speciation 15 , behavior 1 , endocrinology 16 , ecotoxicology 17 , immunology 18 and parasitology 19 . Future studies in each of these fields will benefit from the ability to perform functional genetic manipulations in sticklebacks.…”