Modulation of Disabled-1 Activity by Alternative Splicing

• Author / Creator

  Gao, Zhihua

• The Reelin-Disabled-1 (Dab1) signaling pathway plays a key role in regulating neuronal positioning and synaptic plasticity. Binding of Reelin to its receptors induces tyrosine phosphorylation of the intracellular adaptor protein Dab1. Tyrosine-phosphorylated Dab1 not only rapidly transmits the Reelin signal to downstream effectors but also terminates Reelin-mediated signaling by targeting itself for degradation. Multiple alternatively-spliced Dab1 isoforms have been reported; however, the functions of Dab1 isoforms, other than the commonly studied Dab1 form, remain unknown.
  Here, we show that an alternatively-spliced chicken Dab1 isoform, chDab1-E, is missing two critical tyrosine sites implicated in Reelin signaling, and is not tyrosine phosphorylated upon Reelin stimulation. Knockdown of Dab1-E in chick retina results in a significant reduction in the number of proliferating cells and promotes ganglion cell differentiation, suggesting that chDab1-E is involved in the maintenance of the retinal progenitor pool and retinogenesis. Furthermore, we show that chDab1-E is serine/threonine phosphorylated by cyclin-dependent kinase 2 (Cdk2) independent of Reelin. ChDab1-E phosphorylation destabilizes the protein through proteasome degradation, indicating that Dab1 turnover can be regulated by both Reelin-independent serine/threonine phosphorylation and Reelin-dependent tyrosine phosphorylation. Finally, we demonstrate that Dab1 alternative splicing is highly complex in mouse, with the potential of generating 16 isoforms that differ primarily in the tyrosine-rich region of Dab1. We have identified 11 murine Dab1 isoforms that are differentially phosphorylated on tyrosine residues, suggesting that different Dab1 isoforms may differentially respond to Reelin stimulation.
  We propose that Dab1 alternative splicing provides an exquisitely-regulated mechanism to fine-tune the activity of Reelin signaling in a temporal and spatial manner, allowing cells that express different Dab1 isoforms to differentially respond to the Reelin signal during development. Our studies support diverse roles for alternatively-spliced Dab1 isoforms during central nervous system development. We propose a model whereby Dab1 alternative splicing tightly regulates neurogenesis, neuronal migration and synaptic plasticity through both Reelin-independent and Reelin-dependent signaling events. Our findings provide new insight into the roles of developmentally-regulated alternative splicing in controlling gene function and coordinating complex processes at different developmental stages.

• Subjects / Keywords

  • Retinal development
  • Alternative splicing
  • Reelin
  • Disabled-1
  • Phosphorylation

• Graduation date

  Spring 2011

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3DH14

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.