Expression and regulation of prolactin-like protein messenger RNA in undifferentiated chicken granulosa cells

Prolactin-like protein (PRL-L; LOC417800) is a homolog of PRL in non-mammalian vertebrates and can act as a functional ligand of PRL receptor (PRLR). Despite its widespread expression in extrapituitary tissues, mechanisms of regulation of PRL-L in the chicken ovary remain unknown. In this study, we first examined PRL-L expression in chicken ovarian developing follicles. PRL-L transcript levels were highest (P < 0.05) in follicular walls of <2 mm follicles and progressively declined during follicle maturation. Undifferentiated granulosa cells of 6-8 mm follicles had higher (P < 0.05) PRL-L mRNA levels than differentiated granulosa cells of F3, F2 or F1 follicles. In cultured undifferentiated granulosa cells, levels of PRL-L transcript were increased (P < 0.05) by follicle stimulating hormone (FSH) treatment while were not altered by the addition of luteinizing hormone (LH). In addition, 10 ng/ml non-glycosylated (NG-) and 1 ng/ml glycosylated (G-) PRL increased (P < 0.05) but at higher levels (100 or 1000 ng/ml) both showed no effects on PRL-L expression. Furthermore, 100 ng/ml NG-PRL enhanced (P < 0.05) FSH-induced PRL-L expression, whereas the effects of G-PRL were not significant. These results suggest that PRL-L mRNA is differentially expressed in the follicular hierarchy and its high abundance in undifferentiated granulosa cells is under the regulation of FSH or PRL variants independently or in combination. Moreover, in undifferentiated granulosa cells we also provide evidence for a positive role for PKA, PKC and PI3K signaling while a negative role for ERK2 in mediating FSH stimulation of PRL-L transcription.