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Preproenkephalin A gene expression in rat pineal
1Department of Pharmacology, Medical College of Pennsylvania, Philadelphia.
Abstract:
Preproenkephalin A (ppEnk) mRNA has been identified in extracts of rat pineal gland using oligonucleotides complementary to nonoverlapping regions of this mRNA. The mRNA has an apparent molecular size of 1.4 kb, equivalent to that found in rat brain. Slot-blot analysis, used to determine the relative amount of ppEnk mRNA in several tissues, demonstrated that the pineal contains 70% of the concentration of ppEnk mRNA found in the hypothalamus. Using a highly specific radioimmunoassay, rat pineals were demonstrated to contain approximately 3.5 pg methionine-enkephalin (Met-Enk) per gland. Following enzymatic digestion to release cryptic Met-Enk from larger molecular forms, pineals contained approximately 160 pg Met-Enk per gland. Gel filtration analysis of pineal extracts demonstrated that the peak of the cryptic Met-Enk has a molecular weight of 32 kDa (presumably proenkephalin). These results suggest that in rat pineal ppEnk gene products may contribute to pineal functioning.
Insights
Rat pineal glands contain preproenkephalin A (ppEnk) mRNA, similar to brain tissue. This suggests that ppEnk gene products may play a role in the functioning of the rat pineal gland.
Area of Science:
- Neuroscience
- Molecular Biology
- Endocrinology
Background:
- The pineal gland is a key endocrine regulator.
- Opioid peptides, like methionine-enkephalin (Met-Enk), are involved in various physiological processes.
- The presence and function of opioid peptide precursors in the pineal gland are not well understood.
Purpose of the Study:
- To investigate the presence and quantity of preproenkephalin A (ppEnk) mRNA and its protein products in the rat pineal gland.
- To determine the potential contribution of ppEnk gene products to pineal gland function.
Main Methods:
- Oligonucleotide hybridization to detect ppEnk mRNA in pineal gland extracts.
- Slot-blot analysis to quantify ppEnk mRNA levels in different tissues.
- Radioimmunoassay (RIA) to measure Met-Enk concentrations.
- Gel filtration chromatography to analyze the molecular weight of Met-Enk precursors.
Main Results:
- ppEnk mRNA, 1.4 kb in size, was detected in rat pineal gland extracts, comparable to brain tissue.
- Pineal glands contain 70% of the ppEnk mRNA concentration found in the hypothalamus.
- Rat pineals contain approximately 3.5 pg Met-Enk per gland, increasing to 160 pg after enzymatic digestion of larger forms.
- Gel filtration identified a 32 kDa peak for cryptic Met-Enk, suggesting proenkephalin presence.
Conclusions:
- The rat pineal gland expresses ppEnk mRNA and produces Met-Enk, including cryptic forms likely representing proenkephalin.
- These findings indicate that ppEnk gene products may contribute to the physiological functions of the rat pineal gland.