**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Sex steroid control of reproduction in the sea lamprey

Mara Bryan¹, Roger Bergstedt², and Weiming Li¹

¹ Department of Fisheries and Wildlife, 13 Natural Resources Bldg, Michigan State University, East Lansing, MI, 48824-1222

²USGS-Hammond Bay Biological Station, 11188 Ray Road, Millersburg, MI 49759

Abstract

Sex steroids and their receptors control vital behavioral and physiological functions associated with reproduction in all vertebrates. In the sea lamprey (Petromyzon marinus), two steroids have been identified that play important roles in male reproduction. The first steroid, 15α-hydroxyprogesterone (15α-P), is an unusual progestogen, and is likely the main progestogen in male lampreys. Plasma concentrations of 15α-P were highest in large parasitic phase lampreys, but increased to their highest levels in prespermiating male lampreys injected with gonadotropin-releasing hormones (GnRHs). The nuclear and membrane progestogen receptors (nPR and mPR) in lampreys have mRNA expression patterns that differ by life stage and change after injections of GnRH. PRs in the testis likely play a role in maturation, as time-release implants of progesterone (P, which is converted with high efficiency to 15α-P in vivo) resulted in lampreys achieving spermiation faster than control animals. The high expression levels of both PRs in spermiating male gill and liver may point to a potential role in pheromone production and release. This hypothesis is supported by the extremely high circulating concentrations of pheromone in P-implanted lampreys as compared to lampreys in control groups. The second steroid, androstenedione (Ad), is the direct precursor to testosterone. A nuclear androgen receptor (AR) was identified in the male sea lampreys and characterized using binding assays. Ad was shown to bind to the lamprey AR with high affinity and high specificity. Ad is mainly sequestered in the testis, in association with the AR, and is only circulated in the plasma in relatively small amounts. Lampreys receiving time-release implants of Ad achieved maturation at a faster rate and had larger dorsal rope widths. Knowledge regarding the proximate steroidal controls over reproduction may aid in conceptualizing new alternative control techniques, and can be used make established techniques more efficient.