🧬 Part 1: Introduction to C. elegans

Why C. elegans?

• Tiny soil nematode 🪱, only 1.2 mm long.
• Short lifecycle (~3 days) and short lifespan (~21 days) — great for aging studies!
• Many genes conserved with humans — makes it possible to model human diseases.
• Offers powerful genetic tools 🧪:
  • RNA interference (RNAi) by feeding
  • Mutants readily available
  • CRISPR/Cas9 genome editing
  • Fast genetic crosses and epistasis analysis
  • Transgenics with GFP to follow protein behavior
  • Large-scale RNAi/mutagenesis/compound screens

🧠 The Worm’s Nervous System

• The adult hermaphrodite has 959 total cells, including:
  • 302 neurons
  • 56 neuronal support cells
• Enables studies of touch, memory, learning, and smell.
• Transparent body → ideal for observing neurons and aging in live animals.

🧬 Genome & Reproduction

• Diploid, with 6 chromosomes:
  • Hermaphrodite: 5 pairs of autosomes + 2 X chromosomes
  • Male: 5 pairs of autosomes + 1 X chromosome
• ~100 Mb genome, first multicellular organism fully sequenced!
• ~18,000–19,000 genes identified.
• Germline is the only tissue that remains mitotically active in adults.

🧫 Explore at:

• www.wormbase.org
• www.wormbook.org
• www.wormatlas.org

🧓 Part 2: C. elegans and Aging Studies

Other Model Organisms for Aging

🧫 Yeast | 🪰 Drosophila | 🐁 Mice | 🐷 Pigs | 🐟 Zebrafish | 🐜 Ants | 🦇 Bats | 🧍 Humans

Researchers use different models based on:

• Ethics
• Practicality
• Experimental tools

⚙️ Age-Related Changes in C. elegans

Just like humans, old worms experience:

• Decreased movement 🚶‍♀️
• Muscle loss (sarcopenia) 💪
• Accumulation of oxidized lipids (lipofuscin)
• Protein aggregates 🧩
• Loss of memory 🧠

🔬 Pathways that Determine Aging

Key conserved molecular pathways include:

• Insulin/IGF signaling 🧬 → regulates longevity
• mTOR and dietary restriction pathways
• Mitochondrial function
• Proteostasis mechanisms

🧩 Why are insulin mutants long-lived? Because reduced insulin signaling activates DAF-16/FOXO, which promotes stress resistance and longevity.

💡 GFP Reporters

Two main types help visualize gene expression:

• Transcriptional reporter: promoter + GFP
• Translational reporter: promoter + ORF + GFP Used to study which tissues express certain genes during aging.

🔬 Aging in Muscle: Phalloidin Staining

• Phalloidin binds to F-actin to visualize muscle fibers.
• Aging worms show disorganized or broken muscle structure — evidence of sarcopenia.

🧬 Discovery of Long-Lived Worms

Researchers identify lifespan-extending mutations using:

• Epistasis analysis: defines genetic relationships between pathways.
• CRISPR/Cas9 editing or mutagenesis screens.

💡 Healthspan vs Lifespan: Extending life is not enough — we want worms (and humans) to stay healthy longer, not just live longer.

🧩 Discussion Prompts

• What’s better: random mutagenesis or targeted CRISPR editing? (Mutagenesis = unbiased, but messy; CRISPR = precise, hypothesis-driven.)
• Can we increase healthspan without extending lifespan?
• Should humans even try to extend lifespan indefinitely? 🤔

🧠 Case 1: P25α and Neurodegeneration

• P25α binds to microtubules and is found in brains of Parkinson’s patients 🧠.
• Overexpression in C. elegans causes protein aggregation and neurodegeneration.
• Researchers perform suppressor screens to identify genes that can rescue the degeneration phenotype.
• Cross-species conservation helps map disease mechanisms.

🧬 Case 2: Human Calmodulin Mutations

• Calmodulin is a highly conserved calcium-binding protein.
• C. elegans models used to study human calmodulin mutations introduced via CRISPR/Cas9.
• Different human variants cause distinct effects on worm physiology.
• Next research steps explore their roles in:
  • Aging
  • Endoplasmic reticulum (ER) stress
  • Mitochondrial function
  • Neurodegeneration

🧩 Concept Check

• Do findings translate to humans? Often yes, because many signaling pathways are conserved.
• What is a homolog? A gene in different species that evolved from a common ancestor and performs similar functions.
• Testing homology: replace a worm gene with a human one and check if it restores the phenotype.

🦠 Part 3: Probiotics and Aging

Why Study Probiotics in C. elegans?

The PROHEALTH project aimed to:

1. Find novel probiotic strains 🦠
2. Understand how they affect host longevity — with C. elegans as a test organism!

Advantages:

• Has intestine and innate immune system 🧫
• Eats bacteria → natural setup for host–microbe interaction
• Can be made germ-free
• Powerful genetic toolbox
• Freezer-stable at −80 °C ❄️

🧫 Bacteria as Friend and Foe

• Worms can be colonized with GFP-expressing bacteria (like E. coli) to track infection.
• Colony-forming unit (CFU) counts correlate with GFP intensity — shows infection levels.

🧪 Lactobacillus brevis Extends Lifespan

• 125 bacterial strains screened → 15 increased lifespan!
• Effective strain: L. brevis PH21
• Ineffective control: L. brevis PH23

🦠 Pathogen Protection (MRSA Assay)

• Pre-treat worms with probiotic, then expose to MRSA 🧫.
• Certain strains improve survival significantly (p < 0.0001).

Key immune genes in C. elegans:

• daf-16 (FOXO transcription factor)
• tol-1 (Toll-like receptor)
• pmk-1 (p38 MAPK)
• dbl-1 (TGF-β homolog) → MRSA protection requires dbl-1 pathway activation.

🔍 Molecular Mechanism

Using proteomics (MS), metabolomics (NMR), and STRING network analysis, scientists found:

• Upregulation of pathways in:
  • Organic acid metabolism
  • Serine hydrolase activity
  • Extracellular region
• Enrichment in pathogen susceptibility phenotypes.

🧫 Cross-Species Conservation

Similar beneficial effects of probiotics seen in pig intestinal cell line (IPEC-J2) 🐷 — suggesting relevance beyond worms.

🌍 Shared Mechanisms Across Species

Longevity pathways conserved from yeast to mammals:

🧠 Final Thought

C. elegans might be tiny, but it teaches us massive lessons about:

• Genetics of aging
• Neurodegeneration
• Microbiota-host interactions
• Healthspan vs lifespan balance

🪱💡 “From worm to wisdom — studying the small to understand the big.”