Regulated cationic channel function in Xenopus oocytes expressing Drosophila big brain

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• The neurogenic gene Big brain (bib) is crucial for cell fate determination in Drosophila neurogenesis.
• Mutations in bib lead to neurodevelopmental defects via an unknown mechanism.
• The Big Brain (BIB) protein shares sequence identity with aquaporin channels, suggesting a potential ion transport function.

Purpose of the Study:

• To investigate the functional role of the Big Brain (BIB) protein.
• To elucidate the mechanism by which BIB influences neurogenesis.
• To determine if BIB functions as an ion channel and its regulation.

Main Methods:

• Heterologous expression of BIB in Xenopus oocytes.
• Electrophysiological recordings to assess channel function and ion permeability.
• Treatment with insulin and lavendustin A (tyrosine kinase inhibitor) to study signaling pathways.
• Western blot analysis and confocal microscopy to confirm protein expression and phosphorylation.
• Site-directed mutagenesis to investigate the role of the C-terminus and specific mutations.

Main Results:

• BIB expressed in Xenopus oocytes exhibits voltage-insensitive, nonselective cation channel activity with high permeability to K+.
• Channel conductance is modulated by endogenous signaling pathways, inhibited by insulin, and enhanced by lavendustin A.
• BIB undergoes tyrosine phosphorylation, which is dependent on its C-terminus.
• A nonfunctional BIB mutant (BIB E71N) is expressed on the plasma membrane but does not conduct current.
• Deletion of the C-terminus (amino acids 317-700) abolishes tyrosine phosphorylation and lavendustin A potentiation.

Conclusions:

• The Big Brain (BIB) protein functions as a cation channel.
• BIB activity is regulated by tyrosine kinase-dependent signaling pathways.
• BIB may play a role in transmembrane signaling and membrane depolarization during neurogenesis.