1. House spider genome uncovers evolutionary shifts in the diversity and expression of black widow venom proteins associated with extreme toxicity
Gendreau et al. 2017

2. Latrodectus (genus) Black widows and the Australian red-back
Every continent except Antarctica
Potent venoms
20+ unique latrotoxins and latrodectins
Extreme pain via neurotoxins
Muscle spasms, paralysis, difficulty breathing
Do not mess with black widows, let them do their thing
Arnedo et al 2004, Michalik and Hormiga 2010

3. Rationale Why is their venom extremely potent? Medically important
Understanding the evolution with help with understanding toxicity
Help figure out how venom genes are recruited
How gene families expand
Genetic basis of self-resistance

4. Venom Components Latrotoxins Latrodectins Neurotoxins
α-latrotoxin, α-latroinsectotoxin, δ-latroinsectotoxin, and α-lactrocrustotoxin
Latrodectins
Highly expressed
Contribute to latrotoxin toxicity, but not toxic by themselves

5. Reference Genome Common house spider (Parasteatoda tepidariorum)
Common across the New World
Latrodectus and Parasteatoda split ~90 Mya
Genome Specs: 1.4 Gb
Compared to L. Hesperus (western black widow) and Stegodyphus mimosarum (social velvet spider)

6. Methods
Annotation of house spider genome with 454 and Illumina RNA-Seq data
All tissues/whole bodies at various stages of development
2 RNA-Seq libraries of silk and venom glands (RNA transcripts)
Illumina Hi-Seq 2000 with 100bp paired end reads (150+ million reads each)
RSEM to quantify gene expression
Mapped L. hesperus venom + silk gland, cephalothorax, and S. mimosarum venom RNA transcript reads to respective transcriptomes to ID those with high venom gland expression
tBLASTn search Lhes latrotoxin proteins>translated>BLASTp against NCBI protein database

7. More Methods
BLASTp search of Augustus predicted proteins of Ptep genomes to
Translated Ptep latrotoxins (first 320 bp)
Translated Latrodectus and Steatoda species latrotoxins (first 320 bp)
C-terminal domains of Ptep latrotoxins
Ptep latrodectin homologs
Velvet spider genome for latrodectin and latrotoxin homologs
Protein sequence alignments with CLUSTAL Omega
Use to generate protein phylogenies

8. Results
Identified 47 full-length latrotoxin coding genes in Ptep genome
Latrotoxins vary greatly in structural domains and expression
Significant functional diversification

9. Results
Identified 47 full-length latrotoxin coding genes in Ptep genome
Latrotoxins vary greatly in structural domains and expression
Significant functional diversification
Ptep latrotoxins share significant identity with D. massiliensis, a bacterial endosymbiont of ticks (lateral transfer)

10. Results
Identified 47 full-length latrotoxin coding genes in Ptep genome
Latrotoxins vary greatly in structural domains and expression
Significant functional diversification
Ptep latrotoxins share significant identity with D. massiliensis, a bacterial endosymbiont of ticks (lateral transfer)
α-latrotoxin ortholog not found in Ptep genome
Very different venom compositions

11. Conclusions The house spider has latrotoxin and latrodectin genes
Latrotoxins restricted to one spider family (Theridiidae)
And possibly endosymbiotic bacteria (the assumed source)
Lineage-specific gene family expansion, via gene duplication
Latrodectins are derived from a neuropeptide hormone family
CHH/ITP (Crustacean Hyperglycemic Hormone/Ion Transport Peptide)
Major differences in composition of house spider and black widow venoms
Widows have higher latrotoxin and latrodectin expression
Widows have vertebrate specific α-latrotoxin (venom potency?)

12. Questions
Are there standard cutoffs for what is determined to be tissue-specific or tissue-biased gene expression?
Why is it so difficult to characterize proteins?
They left 30-50% uncharacterized
Are latrodectins inherently toxic or do they just act as enhancers?
Is it possible to resolve how long ago the gene transfer event occurred if DNA reads AND RNA reads are used, and/or more spider species are analyzed? Or is the event too far in the past (assuming ~90 Mya) to expect clear results?