Biology Reference
In-Depth Information
MNP
a
-p-TrkB
Merge
A
B
GC
0s
6s
24s
36s
68s
DIC
fMNP
fMNP
C
0
¢
20
¢
Figure 2.5 Functionalized magnetic nanoparticles are endocytosed and actively trans-
ported in active signaling endosomes. (A) Anti-TrkB antibody functionalized MNPs
(fMNPs) are endocytosed rapidly by BDNF-starved (BDNF()) retinal ganglion cells.
FMNPs are detectable in RGC neurites and growth cones, particularly in the central do-
main, as puncta of varying sizes that colocalize with phospho-TrkB (a-p-TrkB). (B) FMNP
signaling endosomes are trafficked bidirectionally in nascent RGC neurites. Discrete
fMNP puncta are detected in RGC neurites and growth cones (GC). Within neurites,
fMNP signaling endosomes are transported both anterogradely (solid arrowhead)
and retrogradely (open arrowhead) between the soma (right) and growth cone. Time
in seconds (s) is indicated. Scale bars in (A) and (B) are 10 mm. (C) FMNP signaling endo-
somes were detected in some (long arrows) but not other (short arrows) neurites (0
0
). A
constant magnetic field (15 pN) induced fMNPs to evacuate peripheral processes and
coalescence in the cell body and proximal neurites (20
0
). Electromagnet tip was at the
bottom right (shadow). Time in minutes (
0
) is indicated. Scale bar is 10 mm. Reprinted
with permission from the Proceedings of the National Academy of Sciences (
Steketee
et al., 2011
).
contained a single QD-NGF. However, clearly signaling endosomes could
contain more than one QD-NGF, despite their relatively large size
(10-15 nm), highlighting the potential for distinct signaling endosome
identities based solely on the number of neurotrophins per endosome
(e.g.,
Fig. 2.3A
).
Adding to nascent endosome complexity, the number and combination of
neurotrophin receptors per endosome can vary as well (
Formaggio, Cantu,
Chiamulera, & Fumagalli, 2008; Jullien et al., 2003; Watson et al., 1999
)
possibly due to differences in receptor organization in the plasma membrane
(
Mischel et al., 2002; Watson, Porcionatto, Bhattacharyya, Stiles, & Segal,
1999
) and/or the location and method of endocytosis (
Jullien et al., 2003;
