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Localization of c-fos, c-jun, and hsp70 mRNA expression in brain after neonatal hypoxia-ischemia
F Munell1, R E Burke, A Bandele
1Department of Neurology, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Insights
Early response genes c-fos and c-jun, involved in brain plasticity, were co-expressed in injured immature rat brains. Heat shock protein 70 (hsp70) also showed induction but in distinct patterns, suggesting varied cellular responses to injury.
Area of Science:
- Neuroscience
- Molecular Biology
- Developmental Biology
Background:
- Early response genes play critical roles in cellular responses to stimuli.
- Hypoxia and ischemia can induce significant changes in gene expression within the developing brain.
- Understanding these molecular changes is key to comprehending brain injury and recovery mechanisms.
Purpose of the Study:
- To investigate the spatiotemporal expression patterns of immediate early gene (IEG) mRNAs (c-fos, c-jun) and heat-inducible heat shock protein 70 (hsp70) mRNA in the immature brain following hypoxic-ischemic injury.
- To determine the co-localization and temporal relationship of these early response gene expressions.
- To explore the potential role of these genes in brain plasticity and recovery after injury in neonatal rats.
Main Methods:
- Induction of hypoxic-ischemic injury via unilateral carotid artery ligation and hypoxia in 7-day-old rat pups.
- Analysis of gene expression using in situ hybridization on coronal brain sections at various recovery time points (10 min to 24 h).
- Probes used targeted c-fos, c-jun, and hsp70 mRNAs.
Main Results:
- Marked induction and subsequent disappearance of c-fos, c-jun, and hsp70 mRNAs were observed within the 24-hour period.
- Significant co-localization of c-fos and c-jun mRNAs was found in brain regions vulnerable to injury (cortex, hippocampus, striatum) and also in spared regions.
- Hsp70 mRNA expression was induced in most animals positive for IEGs but showed restricted expression patterns, differing from c-fos and c-jun in specific structures and hemispheres.
Conclusions:
- The temporal and regional co-expression of c-fos and c-jun suggests their involvement in regulating gene expression related to brain plasticity, potentially influencing outcomes of injury or recovery in the immature brain.
- While both IEGs and hsp70 are activated, their distinct expression patterns imply specialized functions within different cellular microenvironments following hypoxic-ischemic insult.
- These findings highlight the complex molecular responses in the developing brain to injury and provide insights into the differential roles of early response genes and stress proteins.
Abstract:
The sites of expression of early response mRNAs were determined in the brains of 7-day-old rat pups exposed to unilateral carotid artery ligation followed by 3 h of hypoxia. Pups were sacrificed after recovery periods ranging from 10 min to 24 h. In agreement with our previous northern blot analysis, in situ hybridization of coronal brain sections to probes for c-fos, c-jun, and heat-inducible hsp70 revealed a marked induction and subsequent disappearance of all three mRNAs during this time period. We observed co-localization of the 2 immediate early gene (IEG) mRNAs, c-fos and c-jun, which encode proteins that act in combination to regulate subsequent gene expression. These mRNAs were expressed in all regions known to be vulnerable to permanent injury in this model, such as the cortex, hippocampus, and striatum, as well as in other regions that are spared from permanent damage, such as contralateral cortex and lateral ventricular neuroepithelium. The temporal and regional co-localization of c-fos and c-jun suggests that the transcriptional regulatory activity of their protein products could play a role in plasticity associated with death or recovery from injury in the immature brain. Hsp70 mRNA expression was induced in nearly all of the animals that were positive for IEG mRNAs. Although the most frequent site of expression for all three mRNAs was the ipsilateral cerebral cortex, hsp70 expression was restricted to the ipsilateral hemisphere and absent from a number of structures that were positive for c-fos and c-jun. In addition, the patterns of expression of hsp70 within specific structures frequently differed from those of the IEGs, implying that although both cellular early response systems are activated in this model, their specific functions are carried out within different microenvironments.