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The Sea Lamprey (Petromyzon marinus) Has a Receptor for Androstenedione¹

Department of Fisheries and Wildlife,³ Michigan State University, East Lansing, Michigan 48824 The Centre for Environment, Fisheries and Aquaculture Science,⁴ Weymouth, Dorset DT4 8UB, United Kingdom

ABSTRACT

The use of nuclear steroid receptors as ligand-activated transcription factors is a critical event in vertebrate evolution. It is believed that nuclear steroid receptors arose at or before the vertebrate radiation, except for an androgen receptor (Ar) that evolved only in the gnathostome line. We report an androgen-Ar complex in the male sea lamprey (Petromyzon marinus), an extant jawless vertebrate. The androgen with the highest affinity is not testosterone, but its direct precursor, androstenedione (Ad). To establish that the binding moiety in lamprey testis is a receptor—and not an "androgen-binding protein"—we have shown that it can be extracted from the nucleus as well as the cytosol, that the Ad-receptor complex binds to DNA, and that the receptor is approximately twice the size of an androgen-binding protein extracted from the Atlantic salmon testis. The capacity (and high affinity) of binding of the lamprey Ar is such that much of the Ad present in male lampreys becomes sequestered within the testis (as opposed to circulating in the plasma). Concentrations of Ad (but not of testosterone) in plasma and testis tissue are upregulated by injection of lamprey GnRH. Implantation of male lampreys with exogenous Ad significantly accelerates the development of the testis and growth of at least one secondary male characteristic. It appears that all classes of steroid hormones have contributed to the evolution of the regulatory complexity of steroid receptors found in modern vertebrates.

agnathan, androgen, androgen receptor, androstenedione, lamprey, receptor, steroid hormones, steroid hormone receptors, testis, testosterone

¹Supported by NSF IOB 0450916 and by the Great Lakes Fishery Commission.

Correspondence: ²Weiming Li, Department of Fisheries and Wildlife, 13 Natural Resources Building, Michigan State University, East Lansing, MI 48824. FAX: 517 432 1699; e-mail: liweim{at}msu.edu

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