Transmembrane/juxtamembrane domain-dependent Dscam distribution and function during mushroom body neuronal...

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Drosophila Dscam exhibits extensive isoform diversity due to alternative splicing.
• Dscam function is vital for neuronal wiring and development in Drosophila.
• The role of specific Dscam transmembrane segments in neuronal morphogenesis remains unclear.

Purpose of the Study:

• To investigate the specific roles of Drosophila Dscam isoforms, particularly those containing alternative exon 17 segments, in mushroom body (MB) axonal development.
• To determine how different Dscam isoforms contribute to axonal branching, segregation, and neuronal viability.

Main Methods:

• Generating and expressing Dscam transgenes with specific exon 17 variants (exon 17.1 and exon 17.2) in Dscam mutant Drosophila.
• Analyzing MB neuronal morphogenesis and axonal branching patterns.
• Assessing the rescue of mutant phenotypes, including viability and axonal targeting, by different Dscam transgenes.
• Using Dscam-GFP fusion proteins to track subcellular localization (axons vs. dendrites).

Main Results:

• Exon 4 variations did not significantly impact MB neuronal morphogenesis.
• Dscam transgenes partially rescued Dscam mutant phenotypes.
• The exon 17.2-containing Dscam transgene showed better rescue of axon bifurcation and segregation defects.
• Coexpression of both exon 17.1 and 17.2 transgenes was necessary for rescuing mutant viability.
• Exon 17.1 directed Dscam-GFP to dendrites, while exon 17.2 directed it to axons, with only Dscam[exon 17.2] affecting MB axons.

Conclusions:

• Dscam exon 17.1 has minimal involvement in axonal morphogenesis.
• Dscam exon 17.2 is critical for the development and wiring of Drosophila MB axons.
• Axonal morphogenesis in MBs likely involves multiple distinct Dscam isoforms containing exon 17.2.