Renping Zhou

During development of the nervous system, molecular signals mediating cell–cell interactions play critical roles in the guidance of axonal growth and establishment of synaptic functions. The Eph family of tyrosine kinase receptors and their ephrin ligands has been shown to mediate neuronal interactions in the development of topographic axon projection maps in several brain regions, and the loss of Eph activities result in defects in select axonal pathways. However, effects of deficiencies of the Eph signals on animal behavior have not been well documented. In this study, we showed that inactivation of a ligand of the Eph receptors, ephrin‐A5, resulted in defects in maternal behavior and alterations in anxiety. Female ephrin‐A5 ^−/− mice show significant defects in nest building and pup retrieval. In addition, lower levels of anxiety were observed in both male and female null mice. These changes were not due to deficiencies in estradiol, progesterone or corticosterone levels. Our observations suggest that ephrin‐A5 plays a key role in the development and/or function of neural pathways mediating mouse maternal care and anxiety.

The Eph family of receptor tyrosine kinases plays important roles in neural development. Previous studies have implicated Eph receptors and their ligands, the ephrins, in neuronal migration, axon bundling and guidance to specific targets, dendritic spine formation and neural plasticity. However, specific contributions of EphA5 and EphA6 receptors to the regulation of neuronal cell morphology have not been well studied. Here we show that deletion of EphA5 and EphA6 results in abnormal Golgi staining patterns of cells in the brain, and abnormal spine morphology. These observations suggest novel functions of these Eph receptors in the regulation of neuronal and spine structure in brain development and function.

Purpose.: Primary vitreous regression is a critical event in mammalian eye development required for proper ocular maturity and unhindered vision. Failure of this event results in the eye disease persistent hyperplastic primary vitreous (PHPV), also identified as persistent fetal vasculature (PFV), a condition characterized by the presence of a fibrovascular mass adjacent to the lens and retina, and associated with visual disability and blindness. Here, we identify ephrin-A5 to be a critical regulator for primary vitreous regression. Methods.: Wild-type and ephrin-A5^−/− eyes were examined at various developmental stages to determine the progression of PHPV. Eye tissue was sectioned and examined by H&E staining. Protein expression and localization was determined through immunohistochemistry. Relative levels of Eph receptors were determined by RT-PCR. Results.: Ephrin-A5^−/− animals develop ocular phenotypes representative of PHPV, most notably the presence of a large hyperplastic mass posterior to the lens that remains throughout the lifetime of the animal. The aberrant tissue in these mutant mice consists of residual hyaloid vessels surrounded by pigmented cells of neural crest origin. Labeling with bromodeoxyuridine (BrdU) and detection of proliferating cell nuclear antigen (PCNA) expression shows that the mass in ephrin-A5^−/− animals is mitotically active in embryonic and postnatal stages. Conclusions.: Ephrin-A5 is a critical factor that regulates primary vitreous regression.

The Eph family of receptor tyrosine kinases (RTKs) has been implicated in the regulation of many aspects of mammalian development. Recent analyses have revealed that the EphA2 receptor is a key modulator for a wide variety of cellular functions. This review focuses on the roles of EphA2 in both development and disease.

The cells of the mammalian lens must be carefully organized and regulated to maintain clarity. Recent studies have identified the Eph receptor ligand ephrin-A5 as a major contributor to lens development, as mice lacking ephrin-A5 develop abnormal lenses, resulting in cataracts. As a follow-up to our previous study on the cataracts observed in ephrin-A5−/− animals, we have further examined the morphological and molecular changes in the ephrin-A5−/− lens. Wild-type and ephrin-A5−/− eyes at various ages were fixed, sectioned, and examined using histological techniques. Protein expression and localization were determined using immunohistochemistry and western blot analysis. Lens abnormalities in the ephrin-A5−/− animals are observed at postnatal stages, with lens opacity occurring by postnatal day 21. Structural defects in the lens are first observed in the outer lens fiber cell region where cells in the ephrin-A5−/− lens are severely disorganized. Ephrin-A5 and the Eph receptor EphA2 are expressed during early ocular development and continue to be expressed into postnatal stages. The cataracts in the ephrin-A5−/− mutants occur regardless of the presence of the CP49 mutation. In this follow-up study, we have uncovered additional details explicating the mechanisms underlying ephrin-A5 function in the lens. Furthermore, elucidation of the expression of ephrin-A5 and the Eph receptor EphA2 in the lens supports a fundamental role for this receptor-ligand complex in lens development. These observations, in concert with our previous study, strongly suggest that ephrin-A5 has a critical role in postnatal lens fiber organization to maintain lens transparency.

The cellular and molecular mechanisms underlying the pathogenesis of cataracts leading to visual impairment remain poorly understood. In recent studies, several mutations in the cytoplasmic sterile-α-motif (SAM) domain of human EPHA2 on chromosome 1p36 have been associated with hereditary cataracts in several families. Here, we have investigated how these SAM domain mutations affect EPHA2 activity. We showed that the SAM domain mutations dramatically destabilized the EPHA2 protein in a proteasome-dependent pathway, as evidenced by the increase of EPHA2 receptor levels in the presence of the proteasome inhibitor MG132. In addition, the expression of wild-type EPHA2 promoted the migration of the mouse lens epithelial αTN4-1 cells in the absence of ligand stimulation, whereas the mutants exhibited significantly reduced activity. In contrast, stimulation of EPHA2 with its ligand ephrin-A5 eradicates the enhancement of cell migration accompanied by Akt activation. Taken together, our studies suggest that the SAM domain of the EPHA2 protein plays critical roles in enhancing the stability of EPHA2 by modulating the proteasome-dependent process. Furthermore, activation of Akt switches EPHA2 from promoting to inhibiting cell migration upon ephrin-A5 binding. Our results provide the first report of multiple EPHA2 cataract mutations contributing to the destabilization of the receptor and causing the loss of cell migration activity.