Changes in mRNA levels of ovarian steroidogenic enzymes during artificial maturation of Japanese eel Anguilla japonica

Abstract

Changes in the levels of serum steroids and ovarian steroidogenic enzyme mRNA were analyzed in Japanese eel Anguilla japonica induced to undergo oogenesis by chum salmon pituitary homogenate (SPH) treatment. Serum 17α‐hydroxyprogesterone, 17α,20β‐dihydroxy‐4‐pregnen‐3‐one, androstenedione and estrone levels were barely or not detectable during artificial maturation. In contrast, serum estradiol‐17β (E2) and testosterone (T) levels increased after SPH injections and peaked at the migratory nucleus (MN) stage. 3β‐Hydroxysteroid dehydrogenase mRNA levels did not change between eels in different stages of oogenesis. mRNA levels of P450 cholesterol side‐chain cleavage (P450scc), P450 17α‐hydroxylase/C17‐20 lyase (P450c17), 17β‐hydroxysteroid dehydrogenase type I (17β‐HSD‐I) and P450 aromatase (P450arom) were low before SPH injections. P450scc, P450c17 and 17β‐HSD‐I transcript abundance increased after SPH treatment and peaked at the MN stage. P450arom mRNA levels, however, peaked at the mid‐vitellogenic stage and slightly decreased towards the MN stage. We suggest that these increases in P450scc and P450c17 mRNA levels may account for high T levels at the MN stage. In turn, the high T levels may permit the production of E2 in spite of low P450arom mRNA levels towards the end of oogenesis. Steroidogenesis in artificially maturing eels appears to proceed unlike that in other teleosts, but whether or not this is an artifact remains as yet unknown.

Cloning and characterization of a cDNA encoding cholesterol side-chain cleavage cytochrome P450 (CYP11A1): Tissue-distribution and changes in the transcript abundance in ovarian tissue of Japanese eel, Anguilla japonica, during artificially induced sexual development

“…After SPH treatment commenced, gene expression was induced in the ovaries at the early vitellogenic stage and thereafter transcript abundance further increased in conjunction with the advance of ovarian development, which has been corroborated by real-time quantitative RT-PCR developed in our laboratory [29]. In the mammalian ovary, gene expression of P450scc is highly stimulated by gonadotropin [13,14] and IGF-I [15,16].…”

“…Furthermore, developmental changes in the transcript abundance of P450scc in the ovary during artificially induced oogenesis by SPH was thoroughly examined. Much attention has been paid to the gene regulation of steroidogenic enzymes in the eel ovary by SPH, a hormonal source that potentially contains many species of pituitary peptide hormones and growth factors, which has revealed that these enzymes are differentially transcribed during the progression of oogenesis [6][7][8]29] …”

Effect of thermal regime on the expression of key reproductive genes during hormonally-induced vitellogenesis in female European eels

“…Apart from estrogens, it was demonstrated that also steroids traditionally considered more involved in male physiology, play an important role in female eel maturation, as 11-KT which promotes the previtellogenic ovarian growth (Rohr et al, 2001;Matsubara et al, 2003aMatsubara et al, ,b, 2005Lokman et al, 2007;Kazeto et al, 2011;Setiawan et al, 2012).…”

“…In teleosts, two paralogous genes of P450arom have been found, cyp19a1b, mainly expressed in the brain and cyp19a1a, mainly expressed in the gonad (Chang et al, 1997a;Gelinas et al, 1998; 5 Kishida and Callard, 2001;Blázquez and Piferrer, 2004;Choi et al, 2005). In European and Japanese eels, however, only one aromatase cDNA has been identified (termed cyp19a1), and is expressed in ovary, brain and pituitary Tzchori et al, 2004).Apart from estrogens, it was demonstrated that also steroids traditionally considered more involved in male physiology, play an important role in female eel maturation, as 11-KT which promotes the previtellogenic ovarian growth (Rohr et al, 2001;Matsubara et al, 2003a Matsubara et al., ,b, 2005Lokman et al, 2007; Kazeto et al, 2011;Setiawan et al, 2012).The effect of the androgens can be also mediated by binding to ARs. The gonadal steroids are essential for the teleost reproduction and they are able to affect practically all tissues.…”

“…The fish pituitary injections used to mature female eels provide exogenous gonadotropins directly to the ovaries, and subsequently stimulate ovarian steroid synthesis (Matsubara et al, 2003a;, which not only directly stimulates the oocyte growth but also activates the entire reproductive endocrine axis through feedback mechanisms (review of Zohar et al, 2010). In most female fish the ovarian steroids involved in oocyte growth are testosterone (T) and 17β-estradiol (E2) although 11-ketotestosterone (11-KT) is also important, as it is related to oocyte growth and lipid uptake (Matsubara et al, 2003b;Lokman et al, 2007;Endo et al, 2008) in eel species.…”