Cellular Mechanisms of Development

Chapter 19

Developement

• Growth (cell division)

• Differentiation

• Pattern Formation

• Morphogenesis

Cell Division

• CDK’s control Cell cycle

• Cleavage– Blastomeres– No G Phase in early cell division

C.elegans

Stem Cells

• Tissue specific Stem cells

• Totipotent

• Plouripotent

Blastocyst

• Embryonic Stem Cells

Do plants have Stem Cells?

Cell Differentiation

• First Cell Determination Occurs– Humans have 210 types of cells

• Proteins, morphologies, and functions help us tell them apart

How can we tell if something is Determined?

• Do an experiment– Transplant cells and see what they become– Figure 19.5

Molecular Basis of Determination

• Use transcription factors to change patterns of gene expression.

• Cells become committed to a particular developmental pathway in two ways-– Cytoplasmic determinants from the parents– Cell-cell interactions

Induction

• Animal and Vegetal pole interactions

• Fibroblast growth Factor (FGF)

Reversal of Determination

• Experiments showed that single cells from fully differentiated plants could develop into mature plants

• What about animals?– Frog Experiments– Mammals

Dolly

Steps to cloning Dolly

• 1. Cell containing source DNA was grown on a medium to stop the cell cycle

• 2. Eggs obtained from the ewe were enucleated

• 3.Somatic Cell Nuclear transfer (SCNT)• 29 of 277 fused couplettes formed into

embryos and were implanted into surrogate mother

• 1 lamb was born 5 months later

Problems with Reproductive Cloning

• Low Success Rates

• Large offspring Syndrome

• Develop age related disorders very early– Why

• Lack of Imprinting

Therapeutic Cloning

Stem Cell Research Debate

• What do you think?

The future of Stem Cells

• Adult stem cells may offer an alternative to ES cells

Body Axis

Pattern Formation

• Determines that is going to develop where

• Maternally DeterminedPrefertilization

Postfertilization

Syncytialblastoderm

Cellular Blastoderm

Segmented Embryo

Anterior-Posterior Axis

• Bicoid and Nanos protein gradients

• Hunchback and Caudal maternal messengers– Found evenly throughout the egg

Dorsal- Ventral Axis

• Gurken and Dorsal Proteins– Not what you would expect

Segmentation Genes

• Gap Genes- map out the most basic subdivisions of the embryo

• Pair-rule genes- subdivide the segments made by the gap genes ( ex hairy)

• Segment Polarity Genes- subdidived segments made by P-r genes (ex engrailed)

Homeotic Genes

• Give each segment an identity– Awesome mutations- Untrabithorax and

Antennapedia

Homeotic Gene Complexes

• Bithroax Complex

• Antennapedia complex– HOX genes- refers to all homeobox containing

genes that determine the identity of a body part

– Order of homeobox gene corrosponds to body segment

Plants

• Do not have Hox genes have Mads-box gene

Morphogenesis

• Ordered form and structure

• Regulated in 5 ways– Number, timing, and orientation of cell

divisions– Cell growth and expansion– Changes in cell shape– Cell migration– Cell death

Cell division and Unequal cytokinesis

• This allows cells to be different sizes

Cell death

• Apoptosis vs Necrosis

• When does apoptosis happen?

Cell Migration

• Does not happen in Plants

• Achieved by Cadherins and Integrins

Plants

• Plane of cell division determines morphogenesis– Smaller cell becomes embryo while larger

becomes suspensor– Words to know for AP test Cotyledons and

Apical Meristem

Environmental Effects

• Some Obvious– Jack Pines– Dormant Seeds

• Some not so Obvious– Thalidomide

TSD

• Why is this important? Why now more than in the past?

Endocrine Disrupters

• DDT

• DES

Tissue Development