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Widespread neurotrophin receptor expression in the immune system and other nonneuronal rat tissues
1Department of Neurobiology, Stanford University School of Medicine, California 94305-0388.
Abstract:
RNase protection analysis using p75, trk A, and trk B RNA probes was used to examine mRNA expression in rat tissues, with particular emphasis on the immune system. Every tissue examined, with the exception of postnatal day 0 spleen, expressed p75 mRNA. Trk A mRNA was observed in tissues previously reported to be negative for the trk A receptor, such as kidney, thymus, lymph node, muscle, and lung. Neuronal tissues expressed only the long form of trk A, whereas nonneuronal tissues expressed both trk A forms. Trk B mRNA was expressed by the same tissues as trk A, plus heart and spleen. Neuronal tissues expressed full-length and truncated trk B, whereas nonneuronal tissues only expressed truncated trk B. During development of the thymus p75 mRNA levels increased and trk A mRNA levels decreased. Similarly, for the spleen, p75 mRNA levels increased and those of trk B decreased during development. The expression of p75, trk A and trk B was localized primarily to the stroma of the thymus and spleen, but there was some expression by the splenocytes and thymocytes. The widespread expression of neurotrophin receptors in areas not known to be targets for neurotrophins suggests broader functions for neurotrophins outside of the nervous system.
Insights
Neurotrophin receptors (p75, trkA, trkB) are widely expressed in rat immune tissues, suggesting novel roles beyond the nervous system. Their expression patterns change during thymus and spleen development.
Area of Science:
- Neuroscience
- Immunology
- Molecular Biology
Background:
- Neurotrophin receptors, including p75, trkA, and trkB, are crucial for neuronal development and function.
- Their expression and roles outside the central nervous system are less understood.
- Investigating these receptors in the immune system may reveal new neurotrophin functions.
Purpose of the Study:
- To investigate the mRNA expression of p75, trkA, and trkB in various rat tissues, with a focus on the immune system.
- To analyze the developmental changes in neurotrophin receptor expression in the thymus and spleen.
- To determine the cellular localization of these receptors within immune organs.
Main Methods:
- RNase protection analysis was employed to quantify mRNA levels.
- Specific RNA probes for p75, trkA, and trkB were used.
- Tissue samples from different developmental stages of rats were analyzed.
Main Results:
- p75 mRNA was detected in almost all examined tissues, including the spleen (except at postnatal day 0).
- TrkA mRNA was found in unexpected non-neuronal tissues like kidney, thymus, lymph node, muscle, and lung, with distinct expression of long and short forms.
- TrkB mRNA showed a similar distribution to TrkA, also being present in heart and spleen, with neuronal and non-neuronal tissues expressing different isoforms.
Conclusions:
- The widespread expression of p75, trkA, and trkB in immune tissues suggests neurotrophins have broader functions than previously recognized.
- Developmental studies revealed inverse correlations between p75 and trkA/trkB mRNA levels in the thymus and spleen, respectively.
- These receptors are primarily located in the stroma of the thymus and spleen, with some expression on lymphocytes, indicating potential roles in immune cell function and regulation.