Related Experiment Videos
Cell-free synthesized precursor to somatostatin-28 from the rat hypothalamus
Abstract:
Cell-free translation of rat hypothalamic mRNA and specific immunoprecipitation were used to identify a polypeptide of 16,000 apparent molecular weight as prepro-somatostatin. Quantifying these results suggested that the somatostatin-specific mRNA represented less than 0.01% of the total hypothalamic mRNA. Co-translational addition of microsomal membranes led to the in vitro synthesis of a pro-form of 14,500 molecular weight. By using antisera specifically recognizing 3 different but overlapping segments of somatostatin-28 (SRIF-28), the rat prepro-somatostatin was shown to contain antigenic determinants of this N-terminally extended somatostatin as well as of the tetradecapeptide (SRIF-14). Sequential immunoprecipitation experiments implied the existence of only a single somatostatin precursor among the rat hypothalamic translation products, which would have to be differentially processed to allow release of both SRIF-28 and SRIF-14.
Insights
Researchers identified prepro-somatostatin in rat hypothalamus using cell-free translation. This precursor protein contains elements of both somatostatin-28 and somatostatin-14, suggesting differential processing.
Area of Science:
- Neuroendocrinology
- Molecular Biology
- Protein Chemistry
Background:
- Somatostatin (SRIF) is a peptide hormone with diverse physiological roles.
- The precursor forms and processing of somatostatin in the rat hypothalamus are not fully elucidated.
Purpose of the Study:
- To identify and characterize the somatostatin precursor in rat hypothalamic mRNA.
- To investigate the relationship between different somatostatin forms (SRIF-28 and SRIF-14) and their precursor.
Main Methods:
- Cell-free translation of rat hypothalamic mRNA.
- Immunoprecipitation using specific antisera against somatostatin segments.
- Quantification of somatostatin-specific mRNA abundance.
- Co-translational addition of microsomal membranes.
Main Results:
- A 16,000 molecular weight polypeptide was identified as prepro-somatostatin.
- Somatostatin mRNA constitutes less than 0.01% of total hypothalamic mRNA.
- In vitro synthesis yielded a 14,500 molecular weight pro-form upon addition of membranes.
- Prepro-somatostatin contains antigenic determinants for both somatostatin-28 (SRIF-28) and somatostatin-14 (SRIF-14).
- Sequential immunoprecipitation suggests a single somatostatin precursor is differentially processed.
Conclusions:
- Rat prepro-somatostatin is the direct translation product of hypothalamic somatostatin mRNA.
- The precursor contains sequences for both SRIF-28 and SRIF-14, indicating a common origin.
- Differential processing of a single precursor likely generates the various somatostatin forms observed in the hypothalamus.