Development Model Organisms Model Organisms Used to study - - PowerPoint PPT Presentation

Development

Model Organisms

Model Organisms

• Used to study embryonic development
• Usually reproduce quickly and are easy to

raise in a laboratory setting

• Classic model organisms include:

– Drosophila (fruit fly) – C. elegans (nematode worm) – Saccharomyces (yeast) – Zebrafish

Why do scientists use specific model

• rganisms?
• Genetic similarity to humans
• Easy to house and care for
• Impact of genetic manipulation or drug

treatment is easy to see (transparent embryos)

• Lots of offspring
• Easier to induce genetic changes

Embryonic Development

• Three processes: cell division, cell

determination, cell differentiation, and morphogenesis

Early Embryonic Development

Early Embryonic Development

• Cell division only produces a ball of identical

cells called a blastocyst (or blastula)

• Three germ layers:
• Ectoderm: epidermis, nervous tissue
• Mesoderm: muscle, cartilage, bone, blood

vessels, other connective tissue

• Endoderm: digestive lining, respiratory
• rgans

Stem Cells

• Stem cells are pluripotent: cells capable of

differentiating into any type of cells

• Embryonic stem cells can generate all cell

types

• Adult stem cells generate a limited number of

cell types

Embryonic Stem Cells

How do stem cells differentiate into all the different types of cells?

Early Gene Expression in the Embryo

• What “tells” a cell which genes to express in the

embryo?

• 1. Cytoplasmic Determinants (maternal):

components of the egg cytoplasm (mRNA, proteins, chemicals, etc.) are unevenly distributed to cells during division of the zygote

• 2. Inductive Signals: molecules released by

embryonic cells signal nearby cells to change their gene expression

Cytoplasmic Determinants

• Acts as activators that turn on specific genes
• Internal cue

Inductive Signals

• Signals that change gene expression in a

target cell (external cue) – cells influence

• ther cells, environmental influence
• Influence pattern formation: body plan or

spatial organization of tissues and organs

Determination Differentiation Morphogenesis

Determination

• Cell is “committed” to its cell type (cell fate)

very early in embryonic development, but differentiation is not observable…….yet

• Determination of a cell is under the influence
• f master regulatory genes

Master Regulatory Genes

• Genes that control development by controlling

the expression of other genes

• Examples include:
• myoD
• SRY gene
• homeotic genes (example HOX genes)

myoD

• MyoD is a master regulatory gene involved in

muscle cell determination and differentiation

SRY gene

• Master regulatory gene
• SRY protein acts as a transcription factor to

regulate the expression of genes involved in determining maleness

Homeotic Genes

• Examples of master regulatory genes that

control pattern formation (body plan) in the late embryo, larva, and adult

• Examples include HOX genes

Homeotic Genes

Evolution – Your Favorite Subject!

Determination

• Determined cells then express genes for tissue

specific proteins: found only in a specific cell type, gives the cell its characteristic structure and function (differentiation)

• Determined cells then further differentiate

and become specialists for a specific type of protein

Differentiated Cells Produce Tissue Specific Proteins

Differentiation and Morphogenesis

• Differentiation: cells become specialized in

structure and function

• Morphogenesis: specialized cells are
• rganized into tissues and organs to develop

the form of the organism

• Depends on gene expression and protein

production

Cell Differentiation

• Differences between cell types is due to

differential gene expression

• Regulation of transcription of genes comes

from hormones or other signaling molecules

Morphogenesis

• Process that causes an organism to develop its

shape

• Involves the spatial distribution of cells

Mutations Cause Abnormal Development

• HOX genes play a role in limb pattern

formation

• Mutation in HOXD13 gene results in human

polysyndactyly – Extra fingers or toes and webbed

What are some other factors involved in normal embryonic development?

Other Factors Involved in Development

• Apoptosis
• Changes in gene expression:
• 1. Histone acetylation
• 2. DNA methylation
• 3. microRNAs (miRNAs)

Role of Apoptosis

• Embryonic apoptosis events are highly

programmed and predictable in location, time and amount

• Plays a key role in the morphogenesis of

fingers and toes

• Splits layers of tissues (i.e. lumen of intestine)
• Nervous and immune system – overproduce

cells and then destroy those that don’t function

Apoptosis

microRNAs

• Small sequences of non-protein coding RNA

(~20 nucleotides) that bind to complementary mRNA molecules

• miRNAs are able to block protein translation
• r degrade mRNA and effectively regulate

gene expression