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bcl-XL is the major bcl-x mRNA form expressed during murine development and its product localizes to mitochondria
M González-García1, R Pérez-Ballestero, L Ding
1Department of Pathology, University of Michigan Medical School, Ann Arbor 48109, USA.
Abstract:
Most examples of cell death in animals are controlled by a genetic program that is activated within the dying cell. The apoptotic process is further regulated by a set of genes that act as repressors of cell death. Of these, bcl-2 is expressed in a variety of embryonic and postnatal tissues which suggests a critical role for bcl-2 in organogenesis and tissue homeostasis. Surprisingly, mutant mice with targeted disruption of bcl-2 appear normal at birth and complete maturation of lymphoid tissues before succumbing to fulminant lymphopenia and polycystic renal disease by 2-5 weeks of age. This suggests that there may be genes other than bcl-2 that can regulate apoptosis during development. To begin to investigate this possibility, we have cloned and characterized the murine bcl-x gene, whose human counterpart displays striking homology to bcl-2. The predicted murine bcl-xL gene product exhibits a high level of amino acid identity (97%) to its human counterpart. Just like Bcl-2, the murine bcl-xL gene product can act as a dominant inhibitor of cell death upon growth factor withdrawal. In addition, the bulk of the bcl-xL product localizes to the periphery of mitochondria as assessed by a bcl-xL-tag expression system, suggesting that both Bcl-2 and Bcl-xL proteins prevent cell death by a similar mechanism. bcl-xL is the most abundant bcl-x mRNA species expressed in embryonic and adult tissues. The levels of bcl-xL mRNA appear higher than those of bcl-2 during embryonal development and in several adult organs including bone marrow, brain, kidney and thymus. In addition to bcl-xL, we have identified another form of bcl-x mRNA, bcl-x beta, that results from an unspliced bcl-x transcript. bcl-x beta mRNA is expressed in various embryonic and postnatal tissues. Surprisingly, the expression of bcl-xS (a negative regulator of programmed cell death) was undetectable by a sensitive S1-nuclease assay and polymerase chain reaction analysis of mouse tissues. Based on its tissue and developmental patterns of expression, it appears that bcl-x may play an important role in the regulation of cell death during development and tissue homeostasis.
Insights
Researchers identified the murine bcl-x gene, a homolog of bcl-2, which plays a role in regulating programmed cell death (apoptosis) during development and tissue homeostasis. Its expression patterns suggest a critical function in organogenesis.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- Programmed cell death, or apoptosis, is genetically controlled and regulated by genes like bcl-2.
- Mutant mice lacking bcl-2 show developmental issues, suggesting other regulatory genes exist.
Purpose of the Study:
- To investigate potential regulators of apoptosis beyond bcl-2.
- To clone and characterize the murine bcl-x gene and its role in cell death.
Main Methods:
- Cloning and characterization of the murine bcl-x gene.
- Amino acid identity comparison with human bcl-x.
- Assessing bcl-xL protein localization using a bcl-xL-tag expression system.
- Analyzing bcl-x mRNA expression patterns (bcl-xL, bcl-x beta, bcl-xS) via S1-nuclease assay and PCR.
Main Results:
- Murine bcl-xL shows 97% amino acid identity to human bcl-xL and inhibits cell death upon growth factor withdrawal.
- bcl-xL protein localizes to mitochondria, similar to Bcl-2.
- bcl-xL is the predominant bcl-x mRNA species, with higher expression than bcl-2 in development and certain adult tissues.
- A shorter splice variant, bcl-x beta, was detected, but bcl-xS was undetectable.
Conclusions:
- The bcl-x gene, particularly the bcl-xL isoform, is a crucial regulator of apoptosis.
- bcl-xL likely prevents cell death via a mechanism involving mitochondria.
- The expression patterns of bcl-x suggest a significant role in embryonic development and tissue homeostasis.