A Neural Basis for Control of Cichlid Female Reproductive Behavior by Prostaglandin F 2α

Abstract

Summary In most species, females time reproduction to coincide with fertility. Thus, identifying factors that signal fertility to the brain can provide access to neural circuits that control sexual behaviors. In vertebrates, levels of key signaling molecules rise at the time of fertility to prime the brain for reproductive behavior [1–11], but how and where they regulate neural circuits is not known [12, 13]. Specifically, 17α,20β-dihydroxyprogesterone (DHP) and prostaglandin F2α (PGF2α) levels rise in teleost fish around the time of ovulation [10, 14, 15]. In an African cichlid fish, Astatotilapia burtoni, fertile females select a mate and perform a stereotyped spawning routine, offering quantifiable behavioral outputs of neural circuits. We show that within minutes, PGF2α injection activates a naturalistic pattern of sexual behavior in female A. burtoni. We also identify cells in the brain that transduce a prostaglandin signal to mate, and show that the gonadal steroid DHP modulates mRNA levels of the putative receptor for PGF2α (Ptgfr). We use CRISPR/Cas9 to generate the first targeted gene mutation in A. burtoni, and show that Ptgfr is necessary for the initiation of sexual behavior, uncoupling sexual behavior from reproductive status. Our findings are consistent with a model in which PGF2α communicates fertility status via Ptgfr to circuits in the brain that drive female sexual behavior. Our targeted genome modification in a cichlid fish shows that dissection of gene function can reveal basic control mechanisms for behaviors in this large family of species with diverse and fascinating social systems [16, 17].

Cognitive skills and the evolution of social systems

“…Beach, 1976;McCarthy et al, 1986). Juntti et al (2016) showed that, within minutes of prostaglandin F 2α (PGF 2α ) injection, female A. burtoni showed a naturalistic pattern of sexual behavior, as had been shown in other teleosts previously (Stacey, 1976;Cole and Stacey, 1984;Villars et al, 1985;Liley and Tan, 1985;Kidd et al, 2013) (Fig. 10).…”

“…Astatotilapia burtoni is a unique species for understanding the role of social cognition in the evolution of social behavior because: (i) the social system is organized around resource guarding within small colonies of animals, a context that we can simulate well in a laboratory setting (Fernald and Hirata, 1977a,b;Fernald, 1977); (ii) male status is evident to observers because of their bright body color patterns and a lachrymal (eyebar) stripe, so behavior as a function of status is readily quantifiable (see Fig. 1); (iii) the neural systems responsible for social behavior include regulation of gonadotropin releasing hormone 1 (GnRH1)-containing neurons, which, in most species, ultimately controls reproduction -in A. burtoni, the size and connectivity of these neurons are regulated by male social status; (iv) levels of circulating hormones, tissue-specific peptides and DNA expression can be readily measured; and (v) the A. burtoni genome has been sequenced (Brawand et al, 2014), allowing us to measure gene expression in response to social situations (Desjardins et al, 2010), generate transgenic animals (Ma et al, 2015) and use CRISPR to delete key genes (Juntti et al, 2016).…”

“…10). Juntti et al (2016) identified the cells in the preoptic areas of the brain that transduce the prostaglandin signal to trigger mating and showed that the gonadal steroid 17α,20β-dihydroxyprogesterone (DHP) modulates mRNA levels of the putative receptor for PGF 2α (Ptgfr). Doudna and Charpentier (2014) and Jao et al (2013), using the CRISPR/Cas9 method, targeted a gene mutation in A. burtoni to show that Ptgfr is necessary and sufficient for the initiation of sexual behavior, uncoupling sexual behavior from reproductive status.…”

Polygenic sex determination in the cichlid fish Astatotilapia burtoni

“…In any case, A. burtoni should serve as an excellent model for understanding the outcomes of polygenic sex determination for primary and secondary sexual characteristics. The availability of genome editing tools in the species permits mechanistic dissection of genetic variation [84, 85], while decades of research in the species provides a wealth of information regarding sexually dimorphic behavior, physiology, and related gene expression [38, 81, 86–89]. …”

Evolutionary diversity as a catalyst for biological discovery

“…These and many other examples suggest that the biological systems modulating social behavior exhibit functional plasticity across developmental, seasonal, and rapid neuromodulatory timescales in a species-specific fashion. Investigations in alternative species systems have discovered novel mechanisms regulating several forms of social behavioral plasticity at different timescales (Ament et al, 2008; Ben-Shahar, 2005; Carpenter et al, 2014; Juntti et al, 2016; Maruska et al, 2013). For example, Juntti et al recently combined CRISPR/Cas9 and hormonal manipulations to demonstrate the causal role of prostaglandin F2α in modulating the rapid expression of female mating behaviors in Astatotilapia burtoni cichlid fish (Juntti et al, 2016).…”