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GAP-43 expression in the developing rat lumbar spinal cord
M Fitzgerald1, M L Reynolds, L I Benowitz
1Department of Anatomy and Developmental Biology, University College London, U.K.
Insights
Growth-associated protein GAP-43 (Glyceraldehyde-3-phosphate dehydrogenase-43) expression in the developing rat spinal cord highlights axonal growth pathways. Its expression changes dynamically, peaking during active axonal development and declining postnatally, except in the corticospinal tract.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- Growth-associated protein GAP-43 (Glyceraldehyde-3-phosphate dehydrogenase-43) is crucial for axonal growth and regeneration.
- Understanding its spatiotemporal expression patterns provides insights into neural development and pathway formation.
Purpose of the Study:
- To investigate the expression patterns of GAP-43 in the developing rat lumbar spinal cord from embryonic day 11 (E11) to postnatal day 29 (P29).
- To correlate GAP-43 expression with specific developmental events, including axonal growth, pathway selection, and target innervation.
Main Methods:
- Immunocytochemistry was used to detect and visualize GAP-43 expression in fixed tissue sections.
- The study spanned a critical developmental window, encompassing both embryonic and early postnatal periods.
Main Results:
- Early GAP-43 expression (E11-14) was localized to specific neuronal populations and their axons, including dorsal root ganglia and motoneurons.
- Expression intensity correlated with axonal growth, clearly delineating developmental pathways.
- Later fetal stages (E14-19) showed a shift in expression, with decreased staining in peripheral projections and increased expression within the gray and white matter, indicating target finding and pathway refinement.
- Postnatal decline was observed, with sustained expression in the corticospinal tract until P29.
Conclusions:
- GAP-43 expression serves as a reliable marker for active axonal growth and guidance in the developing spinal cord.
- The dynamic changes in GAP-43 localization reflect distinct phases of neuronal development, from initial axon outgrowth to target engagement and circuit formation.
- Sustained GAP-43 expression in the corticospinal tract suggests its continued role in postnatal maturation or plasticity.
Abstract:
The expression of the growth-associated protein GAP-43, detected by immunocytochemistry, has been studied in the developing rat lumbar spinal cord over the period E11 (embryonic day 11), when GAP-43 first appears in the spinal cord, to P29 (postnatal day 29) by which time very little remains. Early GAP-43 expression in the fetal cord (E11-14) is restricted to dorsal root ganglia, motoneurons, dorsal and ventral roots and laterally positioned and contralateral projection neurons and axons. Most of the gray matter is free of stain. The intensity of GAP-43 staining increases markedly as axonal growth increases, allowing clear visualization of the developmental pathways taken by different groups of axons. Later in fetal life (E14-19), as these axons find their targets and new pathways begin to grow, the pattern of GAP-43 expression changes. During the period, GAP-43 staining in dorsal root ganglia, motoneurons, and dorsal and ventral roots decreases, whereas axons within the gray matter begin to express the protein and staining in white matter tracts increases. At E17-P2 there is intense GAP-43 labelling of dorsal horn neurons with axons projecting into the dorsolateral funiculus and GAP-43 is also expressed in axon collaterals growing into the gray matter from lateral and ventral white matter tracts. At E19-P2, GAP-43 is concentrated in axons of substantia gelatinosa. Overall levels decline in the postnatal period, except for late GAP-43 expression in the corticospinal tract, and by P29 only this tract remains stained.