INGEBI   02650
INSTITUTO DE INVESTIGACIONES EN INGENIERIA GENETICA Y BIOLOGIA MOLECULAR "DR. HECTOR N TORRES"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Electrical activity regulates Plexin A3-mediated axon pathfinding in developing zebrafish spinal motor neurons.
Autor/es:
PAOLA V. PLAZAS; N. C. SPITZER
Reunión:
Congreso; XXVIII Congreso Anual de la Sociedad Argentina de Investigacion en Neurociencias; 2013
Resumen:
One of the puzzles in neurosciences is how neuronal
circuits are formed during the development of the nervous system. While the
role of genetic programs in this process is well understood, evidence for a
role of electrical activity is quite limited.
In zebrafish embryos, each
spinal hemisegment contains 3 primary motorneurons (PMN), named CaP, MiP and
RoP, and ~30 secondary motorneurons (SMN). We simultaneously characterized PMN axon
outgrowth and Ca2+ activity during pathfinding behavior in transgenic
Hb9:Gal4/UAS:GCaMP3 embryos. Between 17 hr (PMN axonogenesis) and 24 hr post
fertilization, PMN display two types of spontaneous Ca2+ transients.
Ca2+ waves are generated in both PMN and SMN, with similar durations
and frequencies. In contrast, only PMN exhibit specific patterns of Ca2+
spiking activity at different developmental stages. Suppression of Ca2+
spiking activity by stochastic expression of inward rectifier K+
channels (hKir) in single PMN led to errors in MiP and RoP axon pathfinding.
Errors comprise aberrant branching in 30% of MiPs and intraspinal pathfinding
mistakes in 26% of RoPs. Misguided RoP axons either extend towards the
endogenous exit point but bypass it or orient away from it. Axon trajectories
of hKir-expressing PMN were restored to normal when the activity of nearby
cells was also suppressed; suggesting that an activity-based competition rule
is a key regulator of PMN axon pathfinding.
The guidance receptor PlexinA3 plays a major role in PMN
axon pathfinding. Coinjections of PlexinA3 morpholino (MO) with hKir cDNA
induced a synergistic effect in the
incidence of pathfinding errors compared with embryos injected either with
PlexinA3 MO alone or hKir cDNA alone. Moreover, whole mount in situ hybridizations showed that PlexinA3 expression is not regulated by activity.
Our results provide an in vivo demonstration of the role of spontaneous electrical
activity in axon pathfinding, modulating PlexinA3 signal transduction pathway.