BC 465 Lecture 1

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.

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.

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).

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 ⇒ $G<em>1$ • Small bud ⇒ S phase • Large bud (≈ mother size) ⇒ $G</em>2$
• 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.

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.

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).

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

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.

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.

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.

“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.

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

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).
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.
Non-physiological substrate
• Plastic lacks native extracellular matrix architecture.
Verification tools
• Karyotype/chromosome spreads to check aneuploidy & stability.

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.