5.3 Regulation of the Cell Cycle

LEQ: Why do some eukaryotic cells have genes that encode information for cell death?

• Reading: 5.4, 28.1• Project day wed, fri

• Activator – remember mitosis?– One important observation from your group about the

cell cycle from mitosis lab.– Write on left board

• Key terms: apoptosis, cancer, metastasis

5.3 Regulation of the Cell Cycle

• Apoptosis is programmed cell death:– Initiation of “death” proteins (caspases)

- self-destructive enzymes

– Results in progressive cell destruction- animation

5.3 Regulation of the Cell Cycle

• Volvox parental colony commits suicide – why?

5.3 Regulation of the Cell Cycle

• Competition in a tissue for growth factors “sculpts” a tissue– Loss of “tails”– Finger webbing

webbed fingers

5.3 Regulation of the Cell Cycle

• Leaf senescence (fall) is programmed cell death!

• Leaf development is programmed, seasonal cell growth!

5.3 Regulation of the Cell Cycle

A network of genes controls development, aging and the cell cycle

• Tissues are “sculpted” using molecular signals: – growth promoting– death promoting

• Changes in gene expression/signaling– Abnormal development– aging– disease

5.3 Regulation of the Cell Cycle

• A subdermal fat layer, middle, in a mouse purged of senescent cells. These mice can run much longer and have larger fat deposits

5.3 Regulation of the Cell Cycle

• Fat ebbs during aging when senescent cells remain. Research raises the possibility that attacks on the cells could postpone diseases of aging.

5.3 Regulation of the Cell CycleFig. 47-25a

Apicalectodermalridge (AER)

Limb buds Posterior

AnteriorLimb bud

AER

ZPA

50 µm

5.3 Regulation of the Cell CycleFig. 47-25b

Digits

Anterior

2

34

Posterior

VentralDistal

Dorsal

Proximal

5.3 Regulation of the Cell CycleFig. 47-26a

Host limb bud

Posterior

AnteriorNewZPA

EXPERIMENT

ZPA

Donor limb bud

5.3 Regulation of the Cell CycleFig. 47-26b

2

34

RESULTS

2

34

5.3 Regulation of the Cell Cycle

• How did wing-building change when the cells of the ZPA were transplanted?

• Speculate: how do the cells of the ZPA make wing patterns form?

5.3 Regulation of the Cell Cycle

• Cyclopia is caused by mistake in signals that coordinate cell division across tissues– Sonic hedgehog (signal, ligand)

5.3 Regulation of the Cell Cycle

• Cyclopia can be caused by intake of cyclopamine during pregnancy– Teratogen – disrupts the Sonic hedgehog signal

• Sonic Hedgehog regulates:– brain/face development– Wing-building– Cell division of nervous, connective tissues

5.3 Regulation of the Cell Cycle

Summary:• How does cell cycle regulation assist in the homeostasis

of tissues?• Speculate: why were so few cells observed actively

undergoing mitosis in onion root tips/fish blastulas?