Somatostatin receptor 1-5; expression profiles during rat development

Abstract

Background: Somatostatin acts through five receptor subtypes (SSTRs 1-5). We aimed to investigate SSTRs mRNA expression and protein distribution in whole rat embryos, with special emphasis on the pancreas.

Material and methods: Rat embryos were collected on embryonal days 10, 11, 12, 14, 15, 17, 19, 21, and at birth. Presence of SSTRs was investigated with RT-PCR techniques and immunohistochemistry.

Results: There was no SSTR5 mRNA expression in the whole rat embryos. All SSTR1-5 proteins were observed at embryonal day 10, but the localization varied between the different subtypes. From day 11 to birth SSTRs protein presence increased with time in major structures such as skin and cartilage. It remained similar over time in the heart and liver. In the fetal pancreas mRNA expression of SSTR2 and 4 was detected at day 14, and there was an increase up to birth. Only SSTR1 protein co-localized to a higher extent with the islet hormones studied. SSTR2 was present in all islet endocrine cells except for β-cells. In contrast, the immunostaining for SSTR3-4 was co-localized with insulin and PP, and, finally, SSTR5 with glucagon and pancreatic polypeptide. In mRNA isolated from whole rat embryos SSTR1-2 and SSTR4 expression showed a peak at day 14, while SSTR3 mRNA was not present until day 15.

Conclusion: The present data suggest a role for SSTRs during the development of the rat embryo. Subsequent functional studies may elucidate regulatory roles of specific SSTRs for the growth and differentiation of the pancreas as well as other organs.

Keywords: Development; mRNA expression; pancreas; rat embryo; somatostatin receptors.

Figure 1.

The immunohistochemical staining for SSTR subtypes. A: At embryonal day 11 (SSTR1, magnification 100×); B: day 15 (SSTR2, magnification 16×); and C: day 17 (SSTR5, magnification 16×) in rat embryos. Positive staining by SSTR antibodies is highlighted by red colour. D–G: Structures in rat embryos from day 15 to birth (magnification 200×). D: positive staining of SSTR3 in the lens at day 15. E: The outer part of the skin expresses SSTR4 at day 15; F: part of the eye is positive for SSTR1 at day 19; and G: the outer part of the skin is immunostained for SSTR5 in the newborn.

Figure 2.

Expression of SSTR mRNAs in the embryonic rat pancreas amplified using real-time PCR. A: SSTR1; B: SSTR2; C: SSTR3; D: SSTR4; E: SSTR5. Data are given as mean relative expression (2-Δ(cpssts-cpTBP)) of embryonal pancreases from the same day.

Figure 3.

Expression of SSTR mRNAs of entire rat embryos amplified using real-time PCR. A: SSTR1; B: SSTR2; C: SSTR3; D: SSTR4; E): SSTR5. Embryos pooled from one pregnant rat (n = 11) were considered as one observation.