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Sequence and expression of glutamic acid decarboxylase isoforms in the developing zebrafish
S C Martin1, G Heinrich, J H Sandell
1Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston University Medical Center Hospital, Massachusetts 02118, USA.
The Journal of Comparative Neurology
|June 20, 1998
Summary
Zebrafish possess two glutamic acid decarboxylase (GAD) genes, GAD65 and GAD67, crucial for producing gamma-aminobutyric acid (GABA) in the developing embryo. These genes are expressed across the zebrafish nervous system, indicating early roles for GABA signaling.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- Glutamic acid decarboxylase (GAD) is the enzyme responsible for synthesizing gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the vertebrate nervous system.
- Mammals possess two main GAD isoforms, GAD65 and GAD67, with distinct roles in GABA production and localization.
- The presence and function of multiple GAD isoforms in non-mammalian vertebrates, such as zebrafish, are not fully elucidated.
Purpose of the Study:
- To isolate and characterize zebrafish GAD cDNAs homologous to mammalian GAD65 and GAD67.
- To investigate the expression patterns of zebrafish GAD65 and GAD67 during embryonic development.
- To determine the role of GAD and GABA in early neuronal development and circuitry, particularly in the hindbrain and spinal cord.
Main Methods:
- Isolation and sequencing of two distinct zebrafish GAD cDNAs.
- In situ hybridization to determine the spatial and temporal expression of GAD65 and GAD67 mRNA.
- Immunohistochemistry using antibodies against gamma-aminobutyric acid (GABA) to confirm neurotransmitter localization.
Main Results:
- Two zebrafish GAD cDNAs, sharing over 84% identity with human GAD65 and GAD67, were successfully isolated.
- Both GAD65 and GAD67 were expressed in the early zebrafish embryo during axonogenesis, suggesting a role for GABA before synapse formation.
- GAD65 and GAD67 exhibited distinct but overlapping expression patterns in the forebrain, midbrain, hindbrain, and spinal cord, with GABA production confirmed at all sites.
Conclusions:
- Zebrafish possess two functional GAD genes, GAD65 and GAD67, analogous to mammals.
- These GAD genes are expressed in diverse neuronal populations throughout the developing central nervous system, including novel cells in the caudal hindbrain.
- The findings support a conserved role for GAD and GABA in early neurodevelopment and suggest their involvement in the hindbrain circuitry underlying the escape response.