Interactive roles of fibroblast growth factor 2 and neurotrophin 3 in the sequence of migration, process outgrowth, and axonal differentiation of mouse cochlear ganglion cells

Abstract

A growth factor may have different actions depending on developmental stage. We investigated this phenomenon in the interactions of fibroblast growth factor 2 (FGF2) and neurotrophins on cochlear ganglion (CG) development. The portions of the otocyst fated to form the CG and cochlear epithelium were cocultured at embryonic day 11 (E11). Cultures were divided into groups fed with defined medium, with or without FGF2 and neurotrophin supplements, alone or in combination, for 7 days. We measured the number of migrating neuroblasts and distances migrated, neurite outgrowth, and axonlike processes. We used immunohistochemistry to locate neurotrophin 3 (NT3) and its high-affinity receptor (TrkC) in the auditory system, along with FGF2 and its R1 receptor, at comparable developmental stages in vitro and in situ from E11 until birth (P1) in the precursors of hair cells, support cells, and CG cells. Potential sites for interaction were localized to the nucleus, perikaryal cytoplasm, and cell surfaces, including processes and growth cones. Time-lapse imaging and quantitative measures support the hypothesis that FGF2 alone or combined with neurotrophins promotes migration and neurite outgrowth. Synergism or antagonism between NT3 and other factors suggest interactions at the receptor level. Formation of axons, endings, and synaptic vesicle protein 2 were increased by interactions of NT3 and FGF2. Similar experiments with a mutant overexpressor for FGF2 suggest that endogenous FGF2 supports migration and neurite outgrowth of CG neuroblasts as well as proliferation, leading to accelerated development. The findings suggest interactive and sequential roles for FGF2 and NT3.

Regulation of neuronal excitability by release of proteins from glial cells

“…In this case, however, the effect was inhibited by NGF and enhanced by NT-3 [51]. Further interactions of FGF-2 and NT-3 have been described during development of the cochlear ganglion [52]. Our present observations suggest that the composition of the cocktail of growth factors released by glia after stimulation with thyroid hormone [9] could fine-tune Na þ current density in neurons.…”

Disorganized Innervation and Neuronal Loss in the Inner Ear of Slitrk6-Deficient Mice

“…However, the decrease in the expression of neurotrophins in Slitrk6 -knockout mice was relatively small compared to their dramatic phenotype. Culture experiments identified several candidate molecules (TGF-β, LIF, MCP-1, erythropoietin and Fgf2) that affect the survival and outgrowth of inner ear sensory neurons [30]–[33]. Slitrk6 may regulate the expression of some of those or other unidentified trophic and/or tropic factors that promote neuronal survival and neurite extension in addition to neurotrophins.…”

Role of fibroblast growth factor 8 in neurite outgrowth from spiral ganglion neurons in vitro

“…1 and 3), we observed bipolar and multipolar SGN, which are typical of dissociated SGN (Whitlon et al, 2006) grown in culture and immature SGN (Hossain et al, 2008). …”

“…Previous studies in vitro have implicated other FGFs and neurotrophins in migration, differentiation, neurite outgrowth (Hossain et al 2008; Hossain and Morest 2000; Zhou et al 1996), survival (Pirvola et al 1995) and regeneration of primary auditory neurons (Wang and Green 2011; Wei et al 2007). The role of FGF8 in the nervous system, and particularly in the auditory system, has received less attention.…”