Secretoneurin is a potential paracrine factor from lactotrophs stimulating gonadotropin release in the goldfish pituitary.
Secretoneurin (SN) is a functional neuropeptide derived from the evolutionarily conserved part of precursor protein secretogranin II (SgII). In the time course study, SN (10 nM) stimulates luteinizing hormone (LH) production and secretion after 6 h of static incubation of goldfish pituitary cells. Due to the existence of SN-immunoreactivity (SN-IR) in goldfish lactotrophs, endogenous SN might exert a paracrine effect on LH in the pituitary. In an in vitro immunoneutralization experiment, coincubation with anti-SN antiserum reduces the stimulatory effect of salmon gonadotropin-releasing hormone (sGnRH) on LH release by 64%. Using Western blot analysis, we demonstrate that sGnRH significantly increases the expression of the major SgII-derived peptide (∼57 kDa, with SN-IR) and prolactin (PRL) after 12 h in the static culture of goldfish pituitary cells. Furthermore, there exists a significant correlation between the levels of these two proteins (R = 0.76, P = 0.004). Another ∼30 kDa SgII-derived peptide containing SN is only observed in sGnRH-treated pituitary cells. Consistent with the Western blot analysis results, real-time RT-PCR analysis shows that a 12-h treatment with sGnRH induced 1.6- and 1.7-fold increments in SgII and PRL mRNA levels, respectively. SgII gene expression was also associated with PRL gene expression (R = 0.66; P = 0.02). PRL cells loaded with the calcium-sensitive dye, fura 2/AM, respond to sGnRH treatment with increases in intracellular Ca(2+) concentration level, suggesting a potential mechanism of GnRH on PRL cells and thus SgII processing and SN secretion. Taken together, endogenous lactotroph-generated SN, under the control of hypothalamic GnRH, exerts a paracrine action on neighboring gonadotrophs to stimulate LH release.
Zhao
E
E
Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
Grey
Caleb L
CL
Zhang
Dapeng
D
Mennigen
Jan A
JA
Basak
Ajoy
A
Chang
John P
JP
Trudeau
Vance L
VL
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D037201:Follicle Stimulating Hormone, beta Subunit / Q000378:metabolism; D006054:Goldfish / Q000235:genetics / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D006062:Gonadotropins / Q000235:genetics / Q000378:metabolism*; D052682:Lactotrophs / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D019899:Paracrine Communication; D010902:Pituitary Gland / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053381:Secretogranin II / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
D037201:Follicle Stimulating Hormone, beta Subunit; D006062:Gonadotropins; D009479:Neuropeptides; D012333:RNA, Messenger; D053381:Secretogranin II; C081159:secretoneurin; D007987:Gonadotropin-Releasing Hormone; D011388:Prolactin; D007986:Luteinizing Hormone; D002118:Calcium