Epsin 3 is a novel extracellular matrix-induced transcript specific to wounded epithelia.

Using an in vitro model of keratinocyte activation by the extracellular matrix following injury, we have identified epsin 3, a novel protein closely related to, but distinct from previously described epsins. Epsin 3 contains a domain structure common to this gene family, yet demonstrates novel differences in its regulation and pattern of expression. Epsin 3 mRNA and protein were undetectable in keratinocytes isolated from unwounded skin, but induced in cells following contact with fibrillar type I collagen. The native triple helical structure of collagen was required to mediate this response as cells failed to express epsin 3 when plated on gelatin. Consistent with the reported function of other epsins, epsin 3 was evident in keratinocytes as punctate vesicles throughout the cytoplasm that partially co-localized with clathrin. In addition, epsin 3 exhibited nuclear accumulation when nuclear export was inhibited. In contrast to other known epsins, epsin 3 was restricted to keratinocytes migrating across collagen and down-regulated following cell differentiation, suggesting that expression was spatially and temporally regulated. Indeed, epsin 3 was localized specifically to migrating keratinocytes in cutaneous wounds, but not found in intact skin. Intriguingly, Northern hybridization and reverse transcriptase-polymerase chain reaction experiments indicated that epsin 3 expression was restricted to epithelial wounds or pathologies exhibiting altered cell-extracellular matrix interactions. Thus, we have identified a novel type I collagen-induced epsin that demonstrates structural and behavioral similarity to this gene family, yet exhibits restricted and regulated expression, suggesting that epsin 3 may serve an important function in activated epithelial cells during tissue morphogenesis.

Development of dynorphin-like immunoreactive auditory nerve terminals in the chick.

The novel discovery that auditory nerve terminals in the chick cochlear nucleus magnocellularis (NM) are immunoreactive for the opioid peptide dynorphin (DYN) was recently reported [3]. The present study examines the development of DYN-immunoreactivity (DYN-I) in auditory nerve terminals in NM from embryos through young post-hatch chicks. No DYN-I was observed in NM at embryonic day 13 (E13). DYN-I first appeared at E16 as short flat structures partially surrounding NM cell bodies. Around post-hatch day 1 (P1), these structures had a more rounded, chalice-type of morphology reminiscent of the specialized auditory nerve terminals found in birds, the end-bulbs of Held. At P6, most NM neurons were circumscribed by a prominent DYN-I calyceal-type of ending. By P13, fewer NM cells were ringed by this DYN-I and by the third post-hatch week, there was very little DYN-I in NM. There were no obvious differences in the density of DYN-I terminals across either the rostrocaudal length or the mediolateral width of NM at any age examined. These results suggest that during a restricted time of development, end-bulbs of Held in the chick NM contain DYN.