Current status and evolutionary scenario of gonadotropin receptors in gnathostomes.

<p>The presence of gonadotropin receptors (<i>fshr</i>, <i>lhcgr</i>, <i>lhcgr1</i>, <i>lhcgr2</i>) in representative extant species of gnathostome lineages is shown on the right. In some species, the presence or absence of some gonadotropin receptors could not be assessed, due to the lack of genomic data, and these cases are indicated by a question mark. Two gonadotropin receptors, <i>fshr</i> and <i>lhcgr</i> are present in gnathostomes including chondrichthyans and osteichthyans. They were positioned in tandem in the early osteichthyes. The <i>fshr</i>-<i>lhcgr</i> tandem was maintained after the split between sarcopterygians and actinopterygians. Gene loss of <i>lhcgr</i> in various sauropsid groups led to the presence of only <i>fshr</i> in some extant sauropsids. A duplicated <i>lhcgr</i> was generated by a local gene duplication event in the actinopterygian lineage before the emergence of teleosts. Teleost whole-genome duplication (3R) generated duplicated <i>fshr</i>, <i>lhcgr1</i> and <i>lhcgr2</i>. Multiple and selective gene losses after the 3R led to the maintenance of only a single copy of <i>fshr</i>, <i>lhcgr1</i> and <i>lhcgr2</i> and to the physical separation of the tandem <i>fshr</i>-<i>lhcgr</i>. Additional <i>lhr</i> losses occurred independently through the teleost radiation, <i>i</i>.<i>e</i>. <i>lhcgr1</i> was lost in cyprinidae and <i>lhcgr2</i> in some percomorphs. Recent tetraploidization (4R) event has generated additional copies of <i>lhcgr1</i> in salmonids.