Insulin-like growth factor-I regulates cell proliferation in the developing inner ear, activating glycosyl-phosphatidylinositol hydrolysis and Fos expression.

Abstract

The role of insulin-like growth factors (IGF) was investigated during the early development of the inner ear. IGF-I stimulated growth of otic vesicles that were isolated and cultured in vitro. IGF-I induced DNA synthesis, increased cell number, and mitotic rate in a dose-dependent manner at concentrations between 0.1-10 nM. IGF-II also induced growth but with a lower potency, whereas insulin had no effect. In the presence of IGF-I, otic vesicles developed from stage 18 to stage 21 in 24-h cultures, mimicking the normal mitotic pattern and morphogenesis in vivo. IGF-I also stimulated growth in the cochleovestibular ganglion. Binding of 125I-IGF-I to specific receptors occurred with high affinity. An autoradiographic study of sections from otic vesicles showed radiolabeled IGF-I in the epithelium. Immunoreactivity to IGF-I was detected in the otic vesicle and in the cochleovestibular ganglion. Intracellular signaling mechanisms of IGF were explored by studying the turnover of glycosylated phosphatidylinositols and the expression of Fos oncoprotein. IGF-I rapidly increased Fos levels in cultured otic vesicles. Furthermore, antisense oligonucleotides complementary to c-fos were able to inhibit IGF-I-induced growth. Both IGF-I-induced cell proliferation and Fos expression were blocked by an antiinositol phosphoglycan (alpha-IPG) antibody. This work suggests that IGF-I may be a candidate to regulate proliferative growth of the otic primordium during normal development and that this action requires the sequential modulation of glycosyl-phosphatidylinositol turnover and Fos expression.

A network of growth and transcription factors controls neuronal differentation and survival in the developing ear

“…This lack of regeneration in the adult mammalian inner ear has made cell replacement therapy by transplanting extrinsic stem cells into the inner ear, or by activating intrinsic stem cells residing in the inner ear, an interesting proposition to counteract the degeneration and loss of sensory and neuronal cells (Hu and Ulfendahl, 2006). Several growth factors, including epidermal growth factor (EGF), IGF-I and basic fibroblast growth factor (bFGF) promote the proliferation of embryonic stem cells to produce inner ear precursors (Li et al, 2003a and2003b;Hu et al, 2005), in accordance with observations implicating these factors in the proliferation, differentiation and survival of developing inner ear cells (Leon et al, 1995;Zheng et al, 1997;Hossain and Morest, 2000;Ladher et al, 2000;Varela-Nieto et al, 2004). In particular, IGF-I has been shown to promote neural stem cell proliferation and survival in different contexts and to induce differentiation in combination with neurotrophins (Arsenijevic and Weiss, 1998;Arsenijevic et al, 2001) ( Figure 1A).…”

“…IGF-I and IGF1R are expressed in the developing chicken otic epithelium and CVG (Camarero et al, 2003) and in the postnatal cochlear and vestibular ganglia (Camarero et al, 2001 and reviewed in Varela-Nieto et al, 2003 and. In organotypic cultures of chicken otic vesicles, the addition of exogenous IGF-I causes an increase in cell number in the otic vesicle and its associated CVG, mimicking the normal pattern of in vivo morphogenesis (Leon et al, 1995). Addition of exogenous IGF-I to the isolated chicken CVG increases cell proliferation, causes neurite outgrowth and elevates the expression of the neuronal differentiation marker G4 (Camarero et al, 2003) (Fig.…”

“…Both IGF-I and IGF-II appear to be able to increase the number of neural brain cells and prevent neuronal apoptosis (reviewed in Varela-Nieto et al, 2003;Russo et al, 2005;Ye and D'Ercole, 2006). IGF induces growth and DNA synthesis in a variety of neuronal cell types in vitro, including the neurons of the CVG (Leon et al, 1995). IGF-I shortens the length of the cell cycle in neuronal progenitors during embryonic life and influences the growth of all neural cell types (reviewed in VarelaNieto et al, 2003;Ye and D'Ercole, 2006).…”

IdGene Regulation and Function in the Prosensory Domains of the Chicken Inner Ear: A Link between Bmp Signaling andAtoh1

“…Focal electroporations of HH24-25 otic vesicles were performed ex ovo, with the embryos immobilized over an agarose plate, following a procedure similar to the one described for HH20-21 stages. After electroporation, otic vesicles were dissected out from ectoderm and neural tube and cultured in DMEM supplemented with 10% Fetal Bovine Serum (BioWhittaker Europe), at 37°C in a watersaturated atmosphere containing 5% CO 2 as described previously (Leó n et al, 1995;Pujades et al, 2006) for additional 12-20 h. Vectors used for electroporation were as follows: (1) pCIG-mId3-IRES-GFP (Elisa Martí, Institut de Biologia Molecular de Barcelona-Consejo Superior de Investigaciones Científicas, Barcelona, Spain), a vector carrying the full length of mouse Id3 gene (mId3), used to over-express Id3, (2) pCIG-actALK3-IRES-GFP (T. Schultheiss, Harvard University, Cambridge, MA), a vector carrying a transgene that codes for the constitutively active form of the Bmp receptor ALK3, was used to activate the Bmp pathway, (3) pCIG-GFP vector, expressing a nuclear localized GFP protein was used in control experiments, and(4) BRE-tk-EGFP construct (Elisa Martí), was used to monitor Bmp signaling pathway activation at the transcriptional level. This vector contains a Bmp-responsive element (BRE) consisting of a multimerization of two distinct highly conserved sequences encompassing the genomic regions Ϫ1105/1080 and Ϫ1052/Ϫ1032 of the mouse Id1 promoter.…”

Bone marrow mesenchymal stem cells are progenitors in vitro for inner ear hair cells

“…Alternatively, supporting cells could be induced by the developing hair cells: ectopic hair cells in the greater epithelial ridge induced supporting cell markers in surrounding cells (Woods et al, 2004). The MSCs could be induced to become hair cell progenitors by bFGF, EGF and IGF-1, factors that potentially stimulate the in vivo formation of these progenitors (Leon et al, 1995;Pauley et al, 2003;Zheng et al, 1997), and these progenitors were able to give rise to hair cells after overexpression of Math1. An increase in expression of neural progenitor markers could be caused by expansion of the cells that express these markers or by differentiation of MSCs to the neural progenitor phenotype.…”