POWELL, M. L.; SOWER, S. A.; Univ. of New Hampshire, Durham: The Identification of Corpus Luteum and Determination of Reproductive Steroids in the Gonad of the Atlantic Hagfish, Myxine glutinosa

Hagfish are considered the earliest extant vertebrates. Despite their evolutionary importance little is known about their life history or reproduction. To better understand reproduction in M. glutinosa the objectives of this study were to determine the concentrations of two important reproductive steroids, progesterone and estradiol, in the gonadal tissue and determine reproductive development by histological examination of hagfish that were caught monthly over 18 months. In addition, due to the discovery in our studies of possible corpus lutea in the gonadal tissue, we determined progesterone concentrations from these corpus luteum-like structures. Corpora lutea in nonmammalian vertebrates secrete mainly progesterone thought to be involved in the retention of eggs and down regulation of vitellogenin synthesis. The gonads of the female hagfish were shown to contain a range of developmental stages from oocytes to mature eggs and structures that appear to be spent follicles or corpora lutea in various degrees of involution. Corpus-lutea like structures compared to other ovarian tissue and oocytes had significantly higher progesterone concentrations. Progesterone concentrations decreased over time between February and June 2002. Estradiol levels peaked in January suggesting the initiation of vitellogenesis and possibly the beginning of the next reproductive cycle. These data represent the first evidence of a seasonal reproductive cycle in M. glutinosa and the first report of high concentrations of progesterone produced by “corpus luteum” in the gonad of any hagfish species. Supported by UNH/UME NOAA Sea Grant R/FMD-168 and NA16G1035 and UNH Hubbard Endowed Funds.