Identification and characterization of a novel Delphilin variant with an alternative N-terminus

Delphilin is identified as a Glutamate receptor delta 2 (GluR delta 2) Subunit interacting protein, consisting of a PDZ domain and formin homology (FH) domains 1 and 2, in addition to a C-terminal coiled-coil structure. Delphilin has been shown to be selectively expressed in cerebellar Purkinje cells where it co-localizes with the GlUR delta 2 Subunit at the Purkinje cell-parallel fiber synapses. Although Delphilin specifically interacts with the GluR delta 2 C-terminus via its PDZ domain, the physiological role of the interaction is not yet understood. Here, we report that the Delphilin protein exhibits diversity at its N-terminus by variable usage of the first several exons. Interestingly, the two Delphilin mRNAs which correspond to the first one initially identified (now designated as Delphilin alpha) and the second that contains a newly identified first exon (designated as Delphilin beta), show different chronological expression profiles. Delphilin beta mRNA was not decreased throughout the cerebellar development in vivo and in vitro, while in vivo Delphilin a mRNA gradually decreases following the first postnatal week. Delphilins alpha and beta also revealed different subcellular distribution with sonic overlap. Specifically, the cerebellar synaptosomal membrane fraction contained the Delphilin beta protein. Both Delphilin alpha and beta localized at the dendritic spines with GluR delta 2; however, dendritic shafts in cultured Purkinje cells also included Delphilin beta. In MDCK cells upon becoming confluent, Delphilin a moved to the cell-cell junction area, whereas Delphilin maintained a diffuse distribution pattern throughout the cytoplasm. Taken as a whole, these two different Delphilins seemed to play functionally different roles in developing and matured cerebellar Purkinje cells. (c) 2005 Elsevier B.V. All rights reserved.