کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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2800082 | 1568896 | 2014 | 12 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Identification, tissue distribution and functional characterization of the ghrelin receptor in West African lungfish, Protopterus annectens Identification, tissue distribution and functional characterization of the ghrelin receptor in West African lungfish, Protopterus annectens](/preview/png/2800082.png)
• The ghrelin receptor (GHS-R1a) and its isoform (GHS-R1b) were found in a lungfish.
• GHS-R1a mRNA was mainly detected in the brain, liver, intestine, and gonads.
• GHS-R1b mRNA expression was ubiquitous with 1/20 expression level of GHS-R1a.
• Responsibility of GHSs to lungfish GHS-R1a is higher than that of ghrelin.
• Fasting and increased osmolality by estivation might affect GHS-R1a and 1b mRNA expression.
We identified two ghrelin receptor isoforms, the ghrelin receptor type-1a (GHS-R1a) and its alternative splice form (GHS-R1b) for West African lungfish, Protopterus annectens. Lungfish GHS-R1a and 1b comprised 361 and 281 amino acids, respectively. Lungfish GHS-R1a showed the highest identity to coelacanth GHS-R1a (80.4%). The highest expression of GHS-R1a mRNAs was seen in the brain, liver, ovary, heart, intestine, and gills. GHS-R1b mRNAs were also detected in the same tissues with GHS-R1a, but their expression level was 1/20 that of GHS-R1a. In human embryonic kidney 293 cells transiently expressing lungfish GHS-R1a, rat and bullfrog ghrelin, and two GHS-R1a agonists, GHRP-6 and hexarelin, increased intracellular Ca2+ concentrations. The intensity of the Ca2+ increases induced by GHS-R1a agonists was twice when compared to that induced by ghrelin, although the median effective doses (ED50) were similar, suggesting a long-lasting effect of GHS-R1a agonists with similar affinity. We also examined changes in the GHS-R gene expression during an eight-week estivation. Body weight was slightly lowered, but plasma sodium and glucose concentrations decreased; plasma urea concentration increased significantly 4 weeks after the start of estivation. Overall, expression of GHS-R1a mRNA decreased, but changes in GHS-R1b mRNA expression were inconsistent with those of GHS-R1a during estivation, suggesting an involvement of GHS-R in energy homeostasis, as seen in mammals. Our results suggest that the ghrelin–GHS-R1a system is present in this lungfish although ghrelin has not yet been found. The structure of GHS-R1a is closer to that of tetrapods than Actinopterygian fish, indicating a process of evolution that follows the Crossopterygii such as coelacanth.
Journal: General and Comparative Endocrinology - Volume 209, 1 December 2014, Pages 106–117