Cloning of m-ehk2 from the Murine Inner Ear, an eph Family Receptor Tyrosine Kinase Expressed in the Developing and Adult Cochlea

Abstract

To identify receptor tyrosine kinases (RTKs) present in the murine inner ear, a degenerate polymerase chain reaction (PCR) methodology was employed to clone partial cDNAs encoding RTKs from embryonic day-17.5 mouse whole inner ear RNA. At least 20 distinct TKs were identified within the first 50 subcloned PCR products obtained by this analysis (Davis/Lee et al., 1996). One of the receptor RTKs identified encoded an eph-related kinase not previously described in the mouse. Analysis of full-length cDNAs revealed that this RTK is the mouse homolog of the rat ehk-2 gene product (Maisonpierre et al., 1993). Differences in the carboxyl terminal of the mouse and rat ehk2 RTKs suggest that differential splicing of this gene may occur resulting in transcripts encoding truncated and nontruncated forms of the ehk2 RTK. Multiple transcripts corresponding to this RTK were detected by Northern blot analysis only in the mouse brain. RT-PCR analysis revealed the presence of transcripts encoding this kinase in adult mouse brain, inner ear, testes, ovary, thymus, and spleen. Transcripts encoding this kinase were localized using in situ hybridization to the postembryonic day 1 cochlear ganglion neurons in the inner ear and to neurons in discrete regions of the nervous system. This is the first report of eph-related RTK in inner ear tissue that is present in both the developing and adult inner ear tissue. Because this is a member of a family of RTKs that is implicated in establishing the specificity of neuron-target cell interactions (Garrity and Zipursky, 1995), additional studies to determine if the ehk-2 gene product is involved in such processes in the murine cochlea are warranted.

Comparison of Ephrin-A ligand and EphA receptor distribution in the developing inner ear

“…The mammalian inner ear is a structure that develops from a simple, epithelial sac to a highly complex labyrinth comprising five vestibular organs (the utricular and saccular maculae and the three cristae ampullares) that regulate balance, and the coiled, snail-shaped cochlea that regulates hearing. Several studies have reported the expression of various Eph molecules in the early embryonic inner ear (Ciossek et al, 1995;Lee et al, 1996;Henkemeyer et al, 1994;Pickles and van Heuman, 1997; Bianchi and Gale, 1998). However, the role of the Eph family in inner ear development is still unknown.…”

“…Recent studies have reported the presence of several Eph family members in the developing inner ear (Ciossek et al, 1995;Lee et al, 1996;Henkemeyer et al, 1994;Pickles and van Heuman, 1997;Bianchi and Gale, 1998) and mature cochlea (Lee et al, 1996;Bianchi and Gale, 1998). In the present study, the immunohistochemical localization of two ephrin-A ligands and three EphA receptors was examined in developing and mature vestibular and cochlear regions of the inner ear using available antisera.…”

Neuronal Circuitries During Inner Ear Development

“…Another family of proteins, ephrins and Eph receptors, acting through forward or reverse signaling pathways, have also been proposed to play a critical role in patterning auditory innervation (Bianchi and Gale, 1998;Lee et al, 1996;Pickles, 2003). EphB receptors in particular have been shown to influence the outgrowth of SAG fibers in vitro through interaction with ephrin-B1 (Bianchi and Gray, 2002), and disruption of EphB/ ephrin-B interactions results in aberrant cochlear innervation patterns (Zhou et al, 2011).…”

Structure and development of cochlear afferent innervation in mammals

“…Another family of proteins, ephrins and Eph receptors, acting through forward or reverse signaling pathways, have also been proposed to play a critical role in patterning auditory innervation (14,16,90,126,127). Especially, EphB receptors have been shown to influence outgrowth of SAG fibers in vitro through interaction with ephrin-B1 (15), and disruption of ephrin-B/EphB interactions results in aberrant cochlear innervation patterns (197).…”