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.
Highlights
Somatostatin is a cyclic polypeptide hormone with two biologically active forms, somatostatin-14 and the Nterminal extended version, somatostatin-28
SSTR1 protein expression was identified in the neural tube, yolk sac, and aorta on day and 11, and in aorta from day (Figure 1A), while expression in other tissues was detected from day 14–15 and onwards
In whole rat embryos the SSTR mRNA expression was very weak at day 10 but showed a peak already at day 14, followed by a decrease at day 15 in the fetus
Summary
Somatostatin is a cyclic polypeptide hormone with two biologically active forms, somatostatin-14 and the Nterminal extended version, somatostatin-28. The inhibitory effects of somatostatin are mediated by specific G-protein coupled membrane receptors (SSTRs). These SSTRs are able to activate a variety of intracellular signalling mechanisms, leading to different cellular responses. To date five mammalian SSTRs have been cloned, studied, and named according to the order of identification [4,5,6,7] They are distinguished by their pharmacological specificity for different somatostatin analogues, tissue distribution, regulation, and intracellular signalling pathways [2,3,8]. From day 11 to birth SSTRs protein presence increased with time in major structures such as skin and cartilage. Subsequent functional studies may elucidate regulatory roles of specific SSTRs for the growth and differentiation of the pancreas as well as other organs
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