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Expression of the genes for alpha-type and beta-type calcitonin gene-related peptide during postnatal rat brain
J Terrado1, I Gerrikagoitia, L Martinez-Millán
1Department of Anatomy, Embryology and Genetics, Faculty of Veterinary Sciences, University of Zaragoza, Spain.
Insights
This study tracked alpha- and beta-calcitonin gene-related peptide (CGRP) gene expression in developing rat brains. Results show distinct gene expression patterns and suggest CGRP acts as a neuron-derived neurotrophic factor during development.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- Calcitonin gene-related peptide (CGRP) plays roles in neuronal function.
- Understanding CGRP's developmental expression is crucial for insights into brain maturation.
Purpose of the Study:
- To analyze the expression patterns of alpha- and beta-CGRP genes during rat brain postnatal development.
- To compare gene expression with CGRP-like immunoreactivity.
- To investigate the potential role of CGRP as a neurotrophic factor.
Main Methods:
- In situ hybridization histochemistry to detect CGRP messenger RNA (mRNA).
- Immunohistochemistry to detect CGRP-like immunoreactivity.
- Analysis of gene and protein expression across different postnatal developmental stages in rats.
Main Results:
- Both alpha- and beta-CGRP mRNA were detected at birth in specific brain nuclei, with expression patterns changing during development.
- New nuclei expressed alpha-CGRP or both alpha- and beta-CGRP as development progressed.
- CGRP-like immunoreactivity was observed in nuclei with CGRP mRNA, but also in some areas lacking detectable mRNA, suggesting complex CGRP regulation or transport.
Conclusions:
- Rat brain development involves dynamic and differential expression of alpha- and beta-CGRP genes.
- The observed expression patterns, particularly transient expression in the inferior olive, support a role for CGRP as a neuron-derived neurotrophic factor.
- Discrepancies between mRNA and immunoreactivity suggest potential post-transcriptional regulation or CGRP transport between neurons.
Abstract:
In this study we have analysed the expression of the genes for both alpha-type and beta-type calcitonin gene-related peptide (CGRP) during postnatal development of the rat brain and compared it with the expression of CGRP-like immunoreactivity. At birth both alpha-type and beta-type CGRP messenger RNA were present in the parabrachial nucleus, inferior olive and motor nuclei (except for abducens nucleus), and only alpha-type CGRP messenger RNA in some posterior thalamic nuclei. As development advanced, new nuclei started to express either only alpha-CGRP gene (superior olive, parabigeminal, sagulum, and some hypothalamic and cranial thalamic nuclei) or both genes (abducens nucleus). In the inferior olive both genes were transiently expressed. Beta-CGRP messenger RNA disappeared by postnatal day 10 and alpha-CGRP messenger RNA by postnatal day 20. During the whole postnatal development beta-CGRP gene expression predominated over that of alpha-CGRP in the trigeminal and eye motor nuclei, while in the remainder nuclei alpha-CGRP messenger RNA was either the predominant isoform or the sole one. CGRP-like immunoreactivity, which does not distinguish between alpha-type and beta-type CGRP, was detected in those nuclei containing either alpha-CGRP messenger RNA or beta-CGRP messenger RNA. However, no CGRP messenger RNA was detected in areas such as superior colliculus, lateral pontine nucleus, pars reticulata of the substantia nigra, perifornical area, or zona incerta in which CGRP-like immunoreactivity was prominent. CGRP-like immunoreactivity, but not CGRP messenger RNA, was also transiently detected by postnatal day 5 in some cells of the globus pallidus. In the adult brain, the levels of alpha- and beta-CGRP messenger RNA as well as those of CGRP-like immunoreactivity were considerably reduced. This fact, similar to that of other growth- and development-associated factors, suggests a role for CGRP as a neuron-derived neurotrophic factor. The transient expression in neurons of the inferior olive, matching the period when climbing fibres and cerebellar cortex are developing, seems to support such an idea. The results of this study show that those nuclei expressing beta-CGRP gene also express alpha-CGRP gene. However, there are a number of nuclei that only express alpha-CGRP gene. On the other hand, CGRP-like immunoreactivity is detected in some nuclei which express no CGRP messenger RNA. It suggests that such nuclei express any CGRP-related protein (identified by the antibodies against CGRP) or, if they really contain CGRP protein, this is produced from undetectable amounts (using our in situ hybridization histochemistry procedure) of CGRP messenger RNA or it comes from other nuclei that connect with them in which CGRP protein is synthesized and then transferred.