Identification and sequence analysis of prolactin receptor and its differential expression profile at various developmental stages in striped hamsters

Abstract

Prolactin (PRL) plays critical roles in regulation of biological functions with the binding of specific prolactin receptor (PRLR). Revealing the expression patterns of PRLR at different developmental stages is beneficial to better understand the role of PRL and its mechanism of action in striped hamsters. In this study, the cDNA sequence of PRLR (2866-base-pairs) was harvested from the pituitary of mature female striped hamsters (Cricetulus barabensis) that contains an 834-base-pair 5'-untranslated region (1-834 bp), a 1848-base-pair open reading frame (835-2682 bp), and a 184-base-pair 3'-untranslated region (2683-2866). The 1848-base-pair open reading frame encodes a mature prolactin-binding protein of 592 amino acids. In the mature PRLR, two prolactin-binding motifs, 12 cysteines, and five potential Asn-linked glycosylation sites were detected. Our results showed that the PRLR mRNA quantity in the hypothalamus, pituitary, ovaries, or testis was developmental-stage-dependent, with the highest level at sub-adult stage and the lowest level at old stage. We also found that PRLR mRNAs were highest in pituitary, medium level in hypothalamus, and lowest in ovaries or testis. PRLR mRNAs were significantly higher in males than in females, except in the hypothalamus and pituitary from 7-week-old striped hamsters. Moreover, the PRLR mRNAs in the hypothalamus, pituitary, and ovaries or testis were positively correlated with the expression levels of GnRH in the hypothalamus. These results indicated that the PRLR has conserved domain in striped hamster, but also possesses specific character. PRLR has multiple biological functions including positively regulating reproduction in the striped hamster.

Figure 1. Prolactin receptor (PRLR) cDNA sequence and inferred amino acid sequence of Cricetulus barabensis (n=6). Top sequence is the nucleotide sequence and bottom sequence indicates the deduced amino acid residues. The nucleotide sequence deduced to amino acid residues was open reading frame, including 1848-base-pairs (835-2682 bp). The nucleotide sequence 1-834 bp is in the 5′-untranslated region, and the nucleotide sequence 2683-2866 bp is in the 3′-untranslated region. The signal peptide (1-23 amino acid residues) is marked by an arrow, and the transmembrane domain (234-257 amino acid residues) is underlined by short dashed line. Two conserved amino acid residue sequences at the intracellular domain are underlined by long dashed lines. Two prolactin-binding motifs (WIKWS and WSRWG) at the extracellular domain are marked by solid line. The cysteines are boxed and the Asn-linked glycosylation sites are circled.

Figure 2. Relative expression levels of prolactin receptor (PRLR) mRNA in the hypothalamus, pituitary, and ovaries or testis, and GnRH mRNA in the hypothalamus of the striped hamster at different developmental stages (7 weeks, n=6; 13 weeks, n=6, 1.5 years, n=6) for (A, C, E, G) females and (B, D, F, H) males. The data are reported as means±SE. Different upper-case letters indicate significant differences (P<0.01). (ANOVA).

Figure 3. Relative expression levels of PRLR mRNA among the hypothalamus, pituitary, and ovaries or testis in the striped hamster at different developmental stages (7 weeks, n=6; 13 weeks, n=6, 1.5 years, n=6). Relative PRLR mRNA of the hypothalamus, pituitary, and ovaries from (A) 7-week, (B) 13-week estrous, and (C) 1.5-year female striped hamsters. Relative PRLR mRNA of the hypothalamus, pituitary, and testis from (D) 7-week, (E) 13-week estrous, and (F) 1.5-year male striped hamsters. The data are reported as means±SE. Different lower-case letters (P<0.05) and different upper-case letters (P<0.01) indicate significant differences. (ANOVA).

Figure 4. Relative expression levels of prolactin receptor (PRLR) mRNA between female and male striped hamsters (7 weeks, n=6; 13 weeks, n=6, 1.5 years, n=6) in (A) hypothalamus, (B) pituitary, (C) female ovaries and male testis, and (D) GnRH mRNA in the hypothalamus. The data are reported as means±SE. Different lower-case letters (P<0.05) and different upper-case letters (P<0.01) indicate significant differences (t-test).

Figure 5. Correlations of the relative expression of prolactin receptor (PRLR) in the hypothalamus, pituitary, and ovaries (A-C) with that of GnRH in the hypothalamus of female striped hamsters. Correlations of PRLR mRNA in the hypothalamus, pituitary, and testis (D-F) with that of GnRH mRNA in the hypothalamus of male striped hamsters.