BC 465 Lecture 1

Overview: Scope of the Lecture

  • Goal: brief, practical tour of how modern cell biology is done in real labs.
  • Two focal points covered in the excerpt:
    • WHAT we study – model organisms/systems now common in cell-biology labs (with CSU examples).
    • HOW we study – only introduced here; imaging/techniques will follow in another class.

What Is a “Model Organism/System”?

  • Working definition: any non-human biological system (whole organism, virus, or isolated cells) intentionally used as a proxy to understand human biology.
  • Central motivation: understand human cell biology/biomedical disease while taking advantage of systems that are
    • cheaper, faster, ethically easier,
    • genetically manipulable,
    • positioned at key evolutionary nodes,
    • suitable for both cell-biological & biochemical assays.

General Selection Criteria

  • Ease of maintenance & breeding in the lab.
  • Short generation time (many models cycle in 2\text{–}3\,\text{h} to a few days).
  • Large brood size ⇒ powerful genetics & biochem.
  • Genetic toolkits: genome completely sequenced, libraries of deletions/insertions/GFP tags, efficient transfection or CRISPR.
  • Ability to combine cell biology + biochemistry (e.g.
    extracts, lineage mapping).

Saccharomyces cerevisiae – Budding Yeast

  • Ubiquitous in baking & brewing; also one of the most productive cell-biology tools.
  • Practical advantages
    • Grow from a \approx\$0.50 grocery-store brick.
    • Generation time 2\text{–}3\,\text{h}.
    • Community resources: deletion strains, GFP/RFP libraries for every gene.
  • Unique feature: bud size = cell-cycle stage
    • No bud ⇒ G1 • Small bud ⇒ S phase • Large bud (≈ mother size) ⇒ G2
    • Enabled classical mutant screens in the 1950–60 s that discovered core cell-cycle genes.
  • CSU labs using budding yeast
    • Steven Marcus – motor proteins & spindle positioning.
    • Eric Ross – prion-forming proteins.
    • Lori Starkel (dept. chair) – longevity mutant that blocks ageing.
    • Santiago DiPietro – protein trafficking/endocytosis.

Caenorhabditis elegans – Roundworm

  • 1 mm, hermaphroditic, cheap; breeds itself.
  • Complete cell-lineage map: single P0 zygote → exactly 959 somatic cells; every division recorded.
  • Used for development, organogenesis, body-plan genetics, and apoptosis.
    • 131 cells undergo programmed death; mutants with “extra cells” revealed core apoptosis genes.
  • CSU users
    • Aaron Nishimura – lineage tracing.
    • Ty Montgomery – small regulatory RNAs.
    • Fred Hornley – neuronal development.

Drosophila melanogaster – Fruit Fly

  • Four chromosomes ⇒ simple classical genetics & linkage mapping.
  • Visible phenotypic markers (red vs.
    white eyes, hairy legs) help follow alleles.
  • Short life cycle, inexpensive, but escapees become everyone’s labmates.
  • CSU examples: Susan Sonoda (ion channels/receptors), Noreen Reest (neurobiology).

Danio rerio – Zebrafish

  • Fast, cheap, embryos are optically transparent: live imaging of organ formation.
  • Increasingly popular for vertebrate development & disease.
  • CSU: Debbie Garrity – heart development.

Xenopus (Frog) Oocytes & Eggs

  • Very large; easy to micro-inject & “clamp.”
  • Hormonal priming synchronises eggs at chosen cell-cycle stages.
  • Key biochemical trick: egg extract
    • Centrifuge unfertilized eggs without added buffer ⇒ concentrated cytoplasmic lysate retaining native metabolite/protein concentrations.
    • Lets researchers add/deplete factors while staying in a quasi-cellular environment.
    • Classics of cell-cycle regulation (e.g.
    cyclins, MPF) solved here.
  • Also used in electrophysiology because of size.

Mus musculus – Mouse

  • Mammalian genetics, disease modeling, organ biology.
  • Example from CSU (Santiago DiPietro): pigment-granule (melanosome) biogenesis.
    • Block-1 mutation → “coffee” coat colour.
  • Many cancer labs use engineered or patient-derived mouse models.
  • Phenotypic parallels: KIT gene mutations produce matching pigment patches in mice & humans.

Viruses as Model Systems (Not Organisms)

  • Harness viral simplicity to probe host cell biology.
  • CSU virology focus
    • Chao Ping – HIV-1 replication & trafficking.
    • Olga Pearson – RNA-dependent RNA polymerases.
    • Jenny Nyborg – HTLV and transcriptional control.

Cell-Culture Models

  • “Model” = isolated cells from any species/tissue grown in vitro on plastic or glass.
  • Widely used lines
    • HeLa (human cervical carcinoma) – highly proliferative, almost every lab.
    • ATCC repository holds >4000 authenticated lines.

Key Advantages

  • Reduces animal use.
  • Precisely defined environment (media, serum, temp, even music).
  • Compatible with high-resolution microscopy & innumerable biochemical/functional assays.
  • Cryopreservation ⇒ theoretically infinite storage.

Major Caveats

  1. Cross-contamination & mis-identification
    • A single fast-growing cell (often HeLa) can overtake slower cultures; was epidemic in the late 1990 s.
    • NIH now mandates regular authentication (e.g.
    STR profiling).
  2. Primary-culture senescence – the Hayflick limit
    • Normal somatic cells divide only \approx 20\text{–}30 times (telomere shortening).
    • Common workaround: express telomerase or other oncogenic factors → immortalisation, but introduces unknown side-effects.
    • Rapidly proliferating lines accumulate spontaneous mutations → genetic drift.
  3. Non-physiological substrate
    • Plastic lacks native extracellular matrix architecture.
  4. Verification tools
    • Karyotype/chromosome spreads to check aneuploidy & stability.

Ethical & Practical Themes

  • Model choice balances cost, generation time, genetic tractability, ethical constraints, and physiological relevance.
  • No single system answers every question; cell biologists switch among yeast, worms, flies, fish, frogs, mice, viruses, and cultured cells as complementary lenses onto human biology.