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U. Drescher
either attractive or repellent, depending on the actual receptor composition found on the interacting neurons.
9.5 Segmental Restriction of Motor Axons, Neural Crest,
and Hindbrain Segments
Similar complementary expression patterns of Eph receptors and ligands are seen during pathfinding of motor neuron axons, migration of
neural crest cells, and formation of hindbrain segments.
Motor neuron axons leave the neural tube ventrolaterally and extend
over the anterior half of each somite, thus avoiding posterior somites
expressing EphrinBs. This behavior can be mimicked in vitro in a
modified stripe assay resulting in an avoidance by motor neuron axons
of stripes containing EphrinB ligands (Wang and Anderson 1997). In
hindlimb muscles, EphA4-expressing motor neuron axons avoid regions
of EphrinA2 and EphrinAS expression; in vitro, both ligands have a
growth-inhibitory effect on these motor neuron axons (Ohta et al. 1996;
Ohta et al. 1997). Thus it appears that during motor neuron pathfinding,
both proximally and distally, the Eph family is involved in funneling
these axons to their correct target positions.
A similar situation appears to hold true for trunk neural crest cells,
which likewise express EphB receptors and migrate through the anterior
somites (Krull et al. 1997; Wang and Anderson 1997). In vivo application of function-blocking soluble EphrinB molecules disturbed the segmental pattern of neural crest migration (Krull et al. 1997).
There is complementary expression of EphA4/EphB receptors and
EphrinB ligands in hindbrain segments and in the Xenopus embryo in
streams of branchial neural crest cells migrating to the branchial arches.
These receptors and Ephrins appear to mediate repulsion that prevents
intermingling of odd- and even-numbered hindbrain segments of branchial neural crest streams (Smith et al. 1997).
U. Drescher
either attractive or repellent, depending on the actual receptor composition found on the interacting neurons.
9.5 Segmental Restriction of Motor Axons, Neural Crest,
and Hindbrain Segments
Similar complementary expression patterns of Eph receptors and ligands are seen during pathfinding of motor neuron axons, migration of
neural crest cells, and formation of hindbrain segments.
Motor neuron axons leave the neural tube ventrolaterally and extend
over the anterior half of each somite, thus avoiding posterior somites
expressing EphrinBs. This behavior can be mimicked in vitro in a
modified stripe assay resulting in an avoidance by motor neuron axons
of stripes containing EphrinB ligands (Wang and Anderson 1997). In
hindlimb muscles, EphA4-expressing motor neuron axons avoid regions
of EphrinA2 and EphrinAS expression; in vitro, both ligands have a
growth-inhibitory effect on these motor neuron axons (Ohta et al. 1996;
Ohta et al. 1997). Thus it appears that during motor neuron pathfinding,
both proximally and distally, the Eph family is involved in funneling
these axons to their correct target positions.
A similar situation appears to hold true for trunk neural crest cells,
which likewise express EphB receptors and migrate through the anterior
somites (Krull et al. 1997; Wang and Anderson 1997). In vivo application of function-blocking soluble EphrinB molecules disturbed the segmental pattern of neural crest migration (Krull et al. 1997).
There is complementary expression of EphA4/EphB receptors and
EphrinB ligands in hindbrain segments and in the Xenopus embryo in
streams of branchial neural crest cells migrating to the branchial arches.
These receptors and Ephrins appear to mediate repulsion that prevents
intermingling of odd- and even-numbered hindbrain segments of branchial neural crest streams (Smith et al. 1997).