Melatonin receptor genes (mel‐1a, mel‐1b, mel‐1c) are differentially expressed in the avian germ line

AbstractThe presence of melatonin receptor transcripts (mel‐1a, mel‐1b and mel‐1c) was investigated in primordial germ cells (PGCs), immature and mature oocytes, and sperm of Japanese quail by reverse transcription ‐ polymerase chain reaction (RT‐PCR). The mel‐1a transcript was detected in as few as in a thousand PGCs. Significant differences in the expression of melatonin receptor genes were found in differentiating germ cells: in PGCs only the mel‐1a receptor was expressed, in blastoderms and immature oocytes all three transcripts (mel‐1a, mel‐1b, mel‐1c) were present, while in mature ovulated oocytes the predominant transcript was mel‐1c (with sporadic occurrence of mel‐1a and mel‐1b). In sperm, mel‐1a and mel‐1c were present but mel‐1b was absent. This indicates that the expression of melatonin receptor genes changes throughout the differentiation of PGCs into adult gametes: during oocyte differentiation two additional transcripts, mel‐1b and mel‐1c, are synthesized in addition to mel‐1a, but at oocyte maturation, mel‐1a and mel‐1b are degraded and only mel‐1c remains. During male line (spermatozoa) differentiation mel‐1c is transcribed in addition to mel‐1a, with mel‐1b being completely absent. Since melatonin and the activities of enzymes participating in melatonin synthesis are present in the avian yolk, it is reasonable to suggest a role for this molecule in early avian development and germ line differentiation. We propose that melatonin may act as a signaling molecule regulating some differentiation processes (e.g., cell proliferation, migration, etc.) before the formation of neural and hormonal systems. Mol. Reprod. Dev. 75: 1408–1417, 2008. © 2008 Wiley‐Liss, Inc.