Pheromonal bile acid 3-ketopetromyzonol sulfate primes the neuroendocrine system in sea lamprey

Abstract

Background: Vertebrate pheromones are known to prime the endocrine system, especially the hypothalamic-pituitary-gonadal (HPG) axis. However, no known pheromone molecule has been shown to modulate directly the synthesis or release of gonadotropin releasing hormone (GnRH), the main regulator of the HPG axis. We selected sea lamprey (Petromyzon marinus) as a model system to determine whether a single pheromone component alters the output of GnRH.Sea lamprey male sex pheromones contain a main component, 7α, 12α, 24-trihydroxy-5α-cholan-3-one 24-sulfate (3 keto-petromyzonol sulfate or 3kPZS), which has been shown to modulate behaviors of mature females. Through a series of experiments, we tested the hypothesis that 3kPZS modulates both synthesis and release of GnRH, and subsequently, HPG output in immature sea lamprey.

Results: The results showed that natural male pheromone mixtures induced differential steroid responses but facilitated sexual maturation in both sexes of immature animals (χ(2) = 5.042, dF = 1, p < 0.05). Exposure to 3kPZS increased plasma 15α-hydroxyprogesterone (15α-P) concentrations (one-way ANOVA, p < 0.05) and brain gene expressions (genes examined: three lamprey (l) GnRH-I transcripts, lGnRH-III, Jun and Jun N-terminal kinase (JNK); one-way ANOVA, p < 0.05), but did not alter the number of GnRH neurons in the hypothalamus in immature animals. In addition, 3kPZS treatments increased lGnRH peptide concentrations in the forebrain and modulated their levels in plasma. Overall, 3kPZS modulation of HPG axis is more pronounced in immature males than in females.

Conclusions: We conclude that a single male pheromone component primes the HPG axis in immature sea lamprey in a sexually dimorphic manner.

Figure 1

Sex difference in seasonal steroidal responses after natural pheromone exposure in sea lamprey. Exposure to mature male washings (SMW) for 24 h decreased plasma 15α-hydroxyprogesterone (15α-P) concentrations in immature females in June and July while the same treatment increased 15α-P concentrations in immature males in May and June. Lake Huron water (control) and immature male washings (data not shown) had no effect on 15α-P levels in either sex. Females did not have detectable 15α-P in their plasma early in the spawning season (May), but as the season progressed in June and July, plasma 15α-P concentrations became detectable. In immature males, changes in circulating 15α-P after SMW treatment was greater earlier in the spawning season (May) but diminished in later in the season (July). Sex differences in plasma 15α-P concentrations were significant (p < 0.05). * Statistically significant between pre- and post-treatment level in the same group (p < 0.05).

Figure 2

Sex difference in steroidal responses after exposure to synthesized pheromone component in sea lamprey. Exposure to 3kPZS increased plasma 15α-hydroxyprogesterone (15α-P) concentrations in immature male but not in immature female sea lamprey. Δ15α-P = (post-treatment 15α-P level) - (pre-treatment 15α-P level). * Statistically different from 0 h control group (p < 0.05).

Figure 3

Sex difference in forebrain gene expressions after exposure to synthesized pheromone component in sea lamprey. Exposure to 10^-11 M 3kPZS increased Jun mRNA (2 h, p < 0.05) but decreased lGnRH-III mRNA concentrations (8 h, 48 h, p < 0.05) in the forebrain of immature females (A-C). Exposure to 3kPZS increased GAP49, 50, 58, lGnRH-III, Jun and JNK mRNA concentrations in the forebrain of immature males (D-E). The following data points are statistically different from 0 h control (p < 0.05). D. GAP49: 8 h, 24 h, and 48 h; GAP58: 4 h, 8 h, 24 h & 48 h; GAP50: 24 h; lGnRH-III: 2 4 h & 48 h; Jun: 24 h & 48 h; JNK: 24 h & 48 h. E. GAP49: 8 h & 24 h; GAP58: 8 h & 24 h; GAP50: 8 h, 24 h & 48 h; lGnRH-III: 8 h & 24 h; Jun: 8 h & 24 h; JNK: 8 h & 24 h. F. GAP49: 4 h & 48 h; GAP58: 4 h; lGnRH-III: 4 h; Jun: 48 h.

Figure 4

Sex difference in hindbrain gene expressions after exposure to synthesized pheromone component in sea lamprey. Exposure to 10^-10 M 3kPZS decreased GAP50 mRNA (2 h, 8 h, 24 h, and 48 h, p < 0.05) and JNK mRNA (2 h, 4 h, 8 h, and 24 h, p < 0.05) concentrations in the brain stem of immature females (A-C). Exposure to 3kPZS increased GAP49 & 58, lGnRH-III, Jun and JNK mRNA concentrations in the brain stem of immature males (D-E). The following data points are statistically different from 0 h control (p < 0.05). D. lGnRH-III: 2 h & 48 h; Jun: 48 h; JNK: 2 h, 8 h, 24 h & 48 h. E. GAP58: 48 h; lGnRH-III: 48 h; Jun: 2 h & 48 h; JNK: 2 h, 4 h & 48 h. F. GAP49: 8 h & 24 h; GAP58: 48 h; lGnRH-III: 8 h & 48 h; JNK: 2 h & 8 h.

Figure 5

Differential effects of synthesized pheromone component on plasma and forebrain lGnRH-I concentrations in male sea lamprey. (A) Plasma lGnRH-I concentrations showed various effects after 10^-10 M 3kPZS exposure. Exposure to 10^-10 M 3kPZS increased lGnRH-I concentrations in the forebrain (B) but had no effect in the brain stem (data not shown).

Figure 6

Differential effects of synthesized pheromone component on plasma and forebrain lGnRH-III concentrations in male sea lamprey. (A) Plasma lGnRH-III concentrations showed various effects after 10^-10 M 3kPZS exposure. Exposure to 10^-10 M 3kPZS increased lGnRH-III concentrations in the forebrain (B) but had no effect in the brain stem (data not shown).

Figure 7

A schematic diagram of the evolutionary transition between pheromone and GnRH control from invertebrates to sea lamprey (agnathan) to mammals (gnathostome).