Identification of cell-type specific alternative transcripts in the multicellular alga Volvox carteri

Area of Science:

• Evolutionary Biology
• Molecular Biology
• Genetics

Background:

• Cell type specialization is fundamental in complex organisms, driven by gene expression.
• The alga Volvox carteri exhibits two distinct cell types: germ and soma.
• Previous studies revealed significant transcriptome differences between Volvox cell types.

Purpose of the Study:

• Investigate cell type specific alternative transcript isoforms (CTSAI) as a mechanism for differentiation in Volvox carteri.
• Determine the prevalence and functional significance of CTSAI in Volvox.
• Explore the evolutionary implications of CTSAI in early multicellular organisms.

Main Methods:

• Utilized transcriptomic data and de novo assembly (HISAT2, Ballgown) to identify loci with multiple isoforms.
• Manually curated candidate CTSAI genes to eliminate false positives.
• Experimentally verified CTSAI using semi-quantitative RT-PCR.

Main Results:

• Identified 15 strong candidates for CTSAI, with 3 experimentally verified.
• Found 40 RNA binding protein (RBP) genes with cell type-specific expression, suggesting a role in mediating CTSAI.
• Observed limited overlap in alternative splicing between Volvox carteri and Chlamydomonas reinhardtii.

Conclusions:

• CTSAI is a minor but significant contributor to Volvox cellular differentiation.
• Validated CTSAI examples support existing hypotheses and propose new ones regarding gene product specialization.
• Volvox CTSAI serves as a model for understanding the evolution of alternative isoforms and cell type specialization.