Neurotrophin‐3 receptors in the developing chicken retina

Open Access
Publisher Website
Google Scholar
Abstract
Neurotrophin 3 (NT‐3) had specific high‐affinity receptors (HNT‐3R) in the developing chick retina at all ages between embryonic day (E) 4 and E14. The affinity of HNT‐3R for 125I‐NT‐3 did not change with the developmental state. A dissociation constant (kd) of 13 pM was obtained. However, the amount of HNT‐3R appeared to be developmentally regulated; the number of receptors/cell increased from E4 up to E6–7 (coinciding with the main onset of neuronal differentiation), then decreased until E9 and increased again by E12, when all retinal cells were differentiated. Kinetic and cross‐linking experiments showed that HNT‐3R from two prototypical developmental ages, E7 and E14, were different. E7 and E14 HNT‐3R could be distinguished from each other on the basis of different inhibition patterns of 125I‐NT‐3 binding in the presence of nerve growth factor or brain‐derived neurotrophic factor. Chemical cross‐linking of increasing concentrations of 125I‐NT‐3 to its receptors showed (a) one 100‐kDa band corresponding to neurotrophin low‐affinity receptors in both E7 and E14 cells; (b) one 130‐kDa band also present in both E7 and E14 cells. Densitometric measurements showed that this 130‐kDa band behaved as HNT‐3R in E14 cells (kd∼10 pM) but not in E7 cells (kd≥0.2 nM). Furthermore, the 130‐kDa band in both E7 and E14 retinal cells displayed a trk‐like immunoreactivity. Our data show that, in neurons, one particular neurotrophin may induce different actions mediated through distinct and specific receptors.