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Evidence for a role of truncated trkC receptor isoforms in mouse development
M E Palko1, V Coppola, L Tessarollo
1Neural Development Group, Advanced Bioscience Laboratories-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21701, USA.
Abstract:
The trkC locus encodes several receptors for neurotrophin-3, including the well studied full-length tyrosine kinase isoform, in addition to receptor isoforms lacking the kinase active domain. TrkC receptors are widely expressed throughout mouse development in many different organs. To investigate the function of truncated receptors in vivo and to identify cell types that are biologically responsive to this gene product, we have overexpressed a physiological truncated trkC isoform in the mouse. Mice overexpressing this receptor develop to term but die in the first postnatal days. High levels of transgene expression result in severe developmental defects in the peripheral nervous system and in the heart. The severity of neuronal losses observed in these animals suggests that truncated receptors may act by sequestering neurotrophin, thus, closely relating this mouse model to the neurotrophin-3-deficient one. Lower levels of exogenous truncated receptor in transgenic mice result in a more modest phenotype and, in some neuronal populations, do not cause neural deficits. Taken together, these data suggest that truncated trkC receptor isoforms may have modulatory functions in development.
Insights
Overexpressing truncated TrkC receptors in mice caused severe developmental defects and early death, suggesting a modulatory role for these receptors in neurotrophin-3 signaling during development.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- The trkC gene encodes multiple receptor isoforms for neurotrophin-3 (NT-3).
- These receptors, including full-length tyrosine kinase and truncated forms, are broadly expressed during mouse development.
- The specific in vivo function of truncated TrkC receptors remains largely uncharacterized.
Purpose of the Study:
- To investigate the in vivo function of truncated TrkC receptor isoforms.
- To identify specific cell types responsive to truncated TrkC receptor signaling.
- To elucidate the developmental consequences of overexpressing a truncated TrkC isoform.
Main Methods:
- Overexpression of a physiological truncated trkC isoform in transgenic mice.
- Analysis of developmental phenotypes, including survival, peripheral nervous system development, and cardiac function.
- Assessment of transgene expression levels and correlation with observed defects.
Main Results:
- Mice overexpressing high levels of truncated TrkC receptors survived to term but died postnatally.
- Severe developmental defects were observed in the peripheral nervous system and heart.
- Neuronal loss suggests truncated receptors may sequester neurotrophin-3, mimicking NT-3 deficiency.
- Lower expression levels resulted in milder phenotypes, with some neuronal populations unaffected.
Conclusions:
- Truncated TrkC receptor isoforms may play a modulatory role in mammalian development.
- The function of truncated receptors appears dependent on expression levels and potentially neurotrophin-3 availability.
- This study provides a valuable mouse model for understanding the complex roles of TrkC receptor isoforms.