AP Bio- Regulation 2: Development

Details may vary, but Gastrulation is crucial.

The three primary germ layers will be established.

All tissues and organs will come from these germ layers.

The primitive gut tube ("archenteron") will form.

Plant Tissues

Big Questions

How does a multicellular organism develop from a zygote?

How is the development of an animal different from the development of a plant? How are they similar?

How is the position ("polarity") of the parts of an organism determined?

How does differentiation of cell type occur in animals and plants?

How are genetics and development connected? What about the environment?

Fertilization

Cleavage

"n + n = 2n"

"splitting"

Fertilization events in sea urchins

Fertilization events in mammals

The zygote divides...

And divides...

Gastrulation

"organization"

Animals

Early gastrulation

And divides again, and again

External Development of frog eggs

Overview

Notice any differences?

Sperm releases enzymes from acrosome at tip to penetrate jelly coat of ovum

Fusion of sperm and ovum triggers the formation of an mostly impenetrable "fertilization envelope" by an immediate cortical reaction.

This is the "Fast Block"

At this point, each cell can still become a whole organism ("totipotency")

Animal Development occurs in stages

Development continues after birth, until maturity

Yolk

The fertilized cell is a "zygote"

Gastrulation in Frogs

Gastrulation in Sea Urchins

Mid gastrulation

Internal Development of a Dog Embryo

Cleavage in a frog embryo

The fusion of gametes triggers a massive wave of Calcium ion release across the ovum membrane.

This prevents any other sperm from entering the ovum ("polyspermy").

The process takes 30 seconds

This is the "Slow Block"

The evolution of the amniotic egg was a major adaptation that allowed reptiles (and subsequently birds & mammals) to spend their entire life cycle on land. Four membranes:

• Amnion: Protect fetus
• Chorion: Gas Exchange
• Allantois: Waste Storage
• Yolk: Food Source

Frog embryo shown

(All "Blue" light micrographs depict sea urchin embryos)

Eventually, it's a "morula"

Then, it's a "blastula"

"Inner cell mass"

Complete Gastrula

Umbilicus/Placenta

Protostomes vs. Deuterostomes

Fates of the three primary germ layers (learn this!)

Human

Development

Urchin Larvae

Neurulation &

Organogenesis

"getting fancy"

"how you came to be"

Early events in human development

Neurulation in a frog embryo

Just Think Layers

A major division line among animals.

Deuterostomes: Chordates, Echinoderms

Protostomes: Everyone else

Differences:

• Direction of cleavage
• Fate of blastopore during gastrulation

Gastrulation in a sea urchin

Neurulation: The development of the primitive notochord (in chordates, obviously)

Organogenesis: The development of "somites", patches of cells which will give rise to organs

Organogenesis in a chicken embryo

Neurulation begins with the infolding of the neural plate.

After the neural tube is formed, somite formation is initiated

Gastrulation & Neurulation in a frog

Morphogenesis:

Other

experiments

Implantation is crucial

"things get freaky, easy"

Changes in cell shape during development are referred to as "morphogenesis".

This is a very important aspect of developmental biology (structure and function relationships).

Cells can do all sorts of neat things due to changing shape.

Development progresses

Convergent Extension:

Funky Frog Fetuses:

By manipulating frog embryos at early stages of development, polarity is disturbed (with disturbing ease)

Transplantation of a specific region (the "dorsal lip") onto another embryo leads to a duplication of the embryo in opposite polarity.

Polarity &

Cell Fate

"what goes where and how it's done"

plum size

soda can size

Sesame seed size

The fetus remains small for most of the pregnancy,

only really increasing in mass during the last trimester.

One of the major developmental questions:

• How do cells know where they are in the embryo, and what they should become?

Roughly: Cues from two main sources-

• uneven distribution of protein molecules
• signals from nearby cells ("induction")

Removal of a specific region (the "gray crescent"), leads to an embryo lacking any dorsal structures

The Placenta

Parturition

Fate mapping: done by staining cells in early stage embryos

Limb Development:

Chicken limb development is dependent upon specific "organizer regions"

unequal distribution of proteins in an early stage C. elegans embryo

transplantation of the organizer region (ZPA) leads to limb duplication.

Polarity of frog embryo's is determined by cues present prior to fertilization, and by direction of fertilization

A temporary organ.

fluid is exchanged between mother and fetus.

blood cells are not exchanged

Fate map of the C. elegans embryo (intestine map shown)

Hormonal control of labor

What's true for one chordate...

Any Questions?

Positive or Negative feedback?

Development

And Away We Go

Primary vs. Secondary Growth

Plants

Tissue Structure of young roots

Overview

Since plants are continually growing, distinction is made between "primary" and "secondary" growth

Primary Growth: Growth in a "Vertical" direction, accomplished by the apical meristem of roots and shoots.

Secondary growth: Growth in a "horizontal" direction, accomplished by the lateral mersitem that comprises the vascular and cork cambium.

Parenchymal cells: undifferentiated plant cells

A major difference between monocots and dicots is seen in the organization of root tissue.

Monocots (pictured right) have a layer of parenchymal cells surrounding the vascular cylinder in the middle of the root.

Dicots (pictured left) generally lack this feature.

Plant development continues throughout the plant life cycle

Meristem: Permanently undifferentiated, embryonic tissue.

There is meristematic tissue throughout the plant

Formation of a lateral root

Primary growth of the shoot meristem

leaf primordia-

young leaf organ

axillary bud meristem-

will give rise to lateral stems, if

far enough away from apical bud

Time

Lateral Roots originate from the pericycle, the outermost layer of the vascular cylinder

Tissue Structure of young stems

Primary growth of the root meristem

Apical meristem is in the Zone of Cell Division.

Genetics of Plant Development

We have a better understanding of plant development now than we ever did.

Here are some of the broad strokes

Symmetry & Cell Division

Pretty flowers?

Secondary growth of the vascular cambium leads to development of additional layers of xylem & phloem

initially, xylem is produced more rapidly than phloem

Another major difference between monocots and dicots is seen in the organization of the stem.

Dicot stems (pictured left) have a ring of vascular bundles.

Monocot stems (pictured right) have a scattered bundle pattern

Old thought:

Plane of division affected organ form.

New thought:

Plane isn't so important

Once primary growth of stems is complete, only secondary growth occurs.

Vascular cambium-

produces secondary xylem and phloem

Tissue Structure of leaves

even though these mutants are wacky, the leaves they make look fine

Cork Cambium-

Produces productive bark (periderm)

Flowering is under genetic control.

Mutations in flower pattern formation genes lead to abnormalities

Wood Production

Pattern Formation

"Wood" is built up secondary growth

As a woody plant ("tree") grows, vascular tissue closer to the interior of the tree becomes non functional. This becomes "heartwood".

Vascular tissue nearer to the outside of the tree remains functional ("sapwood").

lignin- a polymer present in the secondary cell walls of woody plants

However...

This is not anything new for us. But here it is (C3 leaf shown).

Why does a tree put on more secondary growth every year?

Any Questions?

Wood is easily the most commercially important non-food plant product

The sequence of the Arabidopsis genome

Dendrochronology

Symmetry is very important in determining cell fate

Symmetry is also important in determining polarity of a developing plant

Normal early divisions are asymmetrical. What happens when they are symmetrical?

Overexpression of the KNOTTED-1 gene in tomato mutants leads to "super compound" leaves compared to the wild type

Arabidopsis is the major model organism for plant development.

• 6 week generation time
• 5000 seeds per plant

first plant genome sequenced.

look at the numbers

Alive

or

Dead?

Animal cells differentiate due to lineage based mechanisms (who they are).

Plant cells differentiate due to position based mechanisms (where they are).

The study of tree rings.

Learn all sorts of things.

Pine tree data: wider rings = hotter years

Conclusions?

Make sure you can

Explain the major phases of animal development.

Demonstrate how differentiation, induction, and morphogenesis all function in development.

Compare development in plants and animals.

Explain the causes and effects of developmental disruptions.

Provide some evidence of genetic control of development in animals and plants.