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Expression of bcl-2, bax, and caspase-3 in the brain of the developing rat
1Department of Psychiatry, University of Iowa College of Medicine, Iowa City, IA 52242-1000, USA.
Abstract:
Naturally occurring neuronal death (NOND) is generally considered to be apoptotic. Apoptosis is an active form of cell death in which the regulation of specific proteins produces anti- or pro-apoptotic signals. Two of the protein families involved in this regulation are the bcl proteins and caspases. A quantitative immunoblotting technique was used to examine the temporal expression of bcl-2, bax, and two isoforms of caspase 3 (an active 20 kDa isoform and the inactive 32 kDa precursor) throughout the developing neuraxis. Long-Evans rat fetuses were collected on gestational day (G) 16 and G19, and pups were harvested on postnatal day (P) 0, P3, P6, P12, P21, and P30. Brains were divided into five segments: cortex, thalamus, midbrain, medulla/pons, and cerebellum. In general, the expression of bax increased and the ratio of bcl-2 expression to bax expression decreased concurrent with published data on the onset of NOND in a given area. The timing of these events was paralleled by an increase in the expression of active caspase 3. Unlike the bcl proteins, caspase 3 expression returned toward fetal levels as the brain matured. The timing of the changes in bcl protein and caspase expression show that both protein families are involved in promoting neuronal death. Reductions in caspase expression (and not bcl-2 and bax expression) are key to ending the period of NOND.
Insights
Naturally occurring neuronal death (NOND) involves bcl proteins and caspases. Caspase expression reduction, not bcl proteins, ends NOND as the brain matures.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Naturally occurring neuronal death (NOND) is a crucial developmental process, typically characterized as apoptosis.
- Apoptosis is regulated by specific protein families, including bcl proteins and caspases, which control cell survival and death signals.
Purpose of the Study:
- To investigate the temporal expression of key regulatory proteins, bcl-2, bax, and caspase 3, during rat brain development.
- To correlate the expression patterns of these proteins with the known timeline of NOND in different brain regions.
Main Methods:
- Quantitative immunoblotting was employed to measure protein levels.
- Expression of bcl-2, bax, and active/inactive caspase 3 isoforms was analyzed in dissected rat brain segments (cortex, thalamus, midbrain, medulla/pons, cerebellum) across various developmental time points (gestational days 16-19, postnatal days 0-30).
Main Results:
- Bax expression generally increased, while the bcl-2/bax ratio decreased, coinciding with the onset of NOND in specific brain areas.
- Increased expression of active caspase 3 paralleled these changes in bcl protein expression.
- Caspase 3 expression levels returned to fetal levels as the brain matured, unlike bcl protein expression.
Conclusions:
- Both bcl protein and caspase families play significant roles in promoting neuronal death during development.
- The reduction in caspase expression, rather than bcl-2 and bax, is critical for terminating the period of NOND as the brain matures.