Containment of extended length polymorphisms in silk proteins

Area of Science:

• Evolutionary biology
• Biochemistry
• Genetics

Background:

• Spider silk genes evolve through duplication and homogenization, creating diverse silk types.
• Allelic and gene variants exist within species, such as in the major ampullate spidroin 1 gene of Nephila clavipes.
• The extent of sequence heterogeneities and their protein manifestation remains largely unknown due to limited prior screening.

Purpose of the Study:

• To investigate the extent of sequence variations in spider silk genes.
• To understand how these variations affect silk protein structure and function.
• To explore the implications of genetic diversity for silk properties and adaptation.

Main Methods:

• Analysis of expanded sample sizes to identify sequence variations.
• Characterization of tri-nucleotide deletions/insertions impacting repetitive units.
• Assessment of major ampullate spidroin 1 gene length variations and population spread.

Main Results:

• Sequence variations, including tri-nucleotide indels, result in altered repetitive unit size and structure in silk proteins.
• Major ampullate spidroins 1 display significant length variability, though extreme variants are rare in populations.
• Evidence suggests multiple, homogenized, and differentially expressed spidroin 1 loci per genome, contributing to silk adaptation.

Conclusions:

• Purifying selection likely stabilizes spidroin 1 gene length for protein integrity and function.
• Differential expression of multiple spidroin 1 loci allows for adaptation in silk composition and properties.
• These evolutionary and genetic mechanisms are also partially observed in the second major ampullate spidroin gene.