Early detection of secretogranin-II (SgII) in the human fetal pituitary: immunocytochemical study using an antiserum raised against a human recombinant SgII.
Secretogranin-II (SgII) is a protein contained within secretory granules of mainly gonadotrophs. The purpose of this study was to determine whether SgII immunoreactivity (SgII-IR) in the human fetal pituitary was temporally related to gonadotropin immunoreactivity. A specific antihuman SgII antiserum was thus required. A complementary DNA clone with an open reading frame for human (h) SgII was synthesized by reverse transcription-polymerase chain reaction from pituitary total RNA. This clone was used to obtain the SgII polypeptide (-9 to 152) as a fusion protein, in a heterologous expression prokaryotic system. Antisera against the fusion protein were raised in rabbits and checked for specificity and sensitivity through Western blotting. Human fetal pituitaries from week 6 of gestation onward were used for immunocytochemical studies. Consecutive semithin sections were treated with the specific antisera against hSgII, beta-endorphin, and hPRL and with monoclonal antibodies to hCG alpha, hLH, and hFSH. SgII immunoreactivity appeared at week 8 and was restricted to pituitary cells expressing beta-endorphin (100% colocalization). At week 9, FSH-positive cells did not contain SgII. From week 10, gonadotrophs progressively exhibited SgII-IR, up to 50% of that in FSH-containing cells at week 26. The granin was never found in PRL cells whatever the stage of development. The present data demonstrate that SgII-IR is detected very early in fetal life; however, the positive cells are not gonadotrophs, but corticotrophs. Within gonadotrophs, SgII appears subsequent to hormones. At birth, more than 90% of SgII-IR cells are represented by corticotrophs and gonadotrophs.