Ephrin-A5 inhibits growth of embryonic sensory neurons

Abstract

EphA-ephrin signaling has recently been implicated in the establishment of motor innervation patterns, in particular in determining whether motor axons project into dorsal versus ventral nerve trunks in the limb. We investigated whether sensory axons, which grow out together with and can be guided by motor axons, are also influenced by Eph-ephrin signaling. We show that multiple EphA receptors are expressed in DRGs when limb innervation is being established, and EphA receptors are present on growth cones of both NGF-dependent (predominantly cutaneous) and NT3-dependent (predominantly proprioceptive) afferents. Both soluble and membrane-attached ephrin-A5 inhibited growth of approximately half of each population of sensory axons in vitro. On average, growth cones that collapsed in response to soluble ephrin-A5 extended more slowly than those that did not, and ephrin-A5 significantly slowed the extension of NGF-dependent growth cones that did not collapse. Finally, we show that ectopic expression of ephrin-A5 in ovo reduced arborization of cutaneous axons in skin on the limb. Together these results suggest that sensory neurons respond directly to A-class ephrins in the limb. Thus, ephrins appear to pattern sensory axon growth in two ways-both directly, and indirectly via their inhibitory effects on neighboring motor axons.

Release of MICAL Autoinhibition by Semaphorin-Plexin Signaling Promotes Interaction with Collapsin Response Mediator Protein

“…The maximal percentage of E7 DRG growth cones collapsed by Sema3A is greater than for ephrin-A5 (Fig. 7D), as expected Takahashi et al, 1998;Munoz et al, 2005). In tMICAL expression studies, a 5 nM concentration of ephrinA5 or Sema3A was used (Fig.…”

RanBPM Contributes to Semaphorin3A Signaling through Plexin-A Receptors

“…Therefore, overexpression of HSV-RanBPM-N3 led to decreased sensitivity to Sema3A compared with GFP controls. EphrinA5 has also been shown to have an inhibitory effect on neurite outgrowth in NGF-dependent DRG neurons (Munoz et al, 2005). Expression of the N3 fragment did not alter the ability of ephrinA5 to attenuate axon growth, thus demonstrating that this effect was specific to Sema3A/Plexin signaling.…”

Isolation and Culture of Dissociated Sensory Neurons From Chick Embryos

“…Another point to consider is the ability of cultured embryonic DRG neurons to change over time in culture. For example, these sensory neurons express different levels of receptors within 48 hr depending upon the presence of select neurotrophins 2,30 . Two subclasses of DRG neurons can be enriched by use of selective neurotrophins in the media 2,12,30 .…”

“…For example, these sensory neurons express different levels of receptors within 48 hr depending upon the presence of select neurotrophins 2,30 . Two subclasses of DRG neurons can be enriched by use of selective neurotrophins in the media 2,12,30 . For example, nerve growth factor (NGF) and neurotrophin-3 (NT3) primarily support the survival of cutaneous and proprioceptive neurons, respectively 33 .…”

“…Thus, data acquisition from live cells can be performed on a microscope with a warmed stage but does not require maintenance of adequate CO 2 levels. Growth cone velocity, collapse 8,16,30 , and calcium levels 17 have been studied in live primary chick sensory neurons isolated by the technique described here. In addition, RNAi can successfully decrease protein levels in cultured chick DRG neurons 34 .…”