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Physiology 10: Development


Andrew Huff

on 26 February 2013

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Transcript of Physiology 10: Development

Development Animals Plants Overview Animal Development occurs in stages
Development continues after birth, until maturity Fertilization Cleavage Gastrulation External Development of frog eggs Internal Development of a Dog Embryo Yolk Umbillicus/Placenta The evolution of the amniotic egg was a major adaptation that allowed reptiles (and subsequently birds & mammals) to spend their entire lifecycle on land. Four membranes:
Amnion: Protect fetus
Chorion: Gas Exchange
Allantois: Waste Storage
Yolk: Food Source
Fertilization events in sea urchins 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" 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" Fertilization events in mammals Notice any differences? The fertilized cell is a "zygote" The zygote divides... And divides... And divides again, and again Eventually, it's a "morula" Then, it's a "blastula" "Inner cell mass" "n + n = 2n" "splitting" "organization" Early gastrulation Mid gastrulation Complete Gastrula 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. Gastrulation in Sea Urchins Gastrulation in Frogs Fates of the three primary germ layers (learn this!) Just Think Layers Protostomes vs. Deuterostomes A major division line among animals.
Deuterostomes: Chordates, Echinoderms
Protostomes: Everyone else
Direction of cleavage
Fate of blastopore during gastrulation "getting fancy" Neurulation &
Organogenesis Neurulation: The development of the primitive notochord (in chordates, obviously)

Organogenesis: The development of "somites", patches of cells which will give rise to organs Neurulation begins with the infolding of the neural plate.

After the neural tube is formed, somite formation is initiated Neurulation in a frog embryo Organogenesis in a chicken embryo Morphogenesis: 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. Convergent Extension: Human
Development "how you came to be" Early events in human development Implantation is crucial Development progresses The fetus remains small for most of the pregnancy,
only really increasing in mass during the last trimester. Sesame seed size plum size soda can size Parturition The Placenta A temporary organ.
fluid is exchanged between mother and fetus.
blood cells are not exchanged Hormonal control of labor Positive or Negative feedback? Polarity &
Cell Fate "what goes where and how it's done" 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") unequal distribution of proteins in an early stage C. elegans embryo Polarity of frog embryo's is determined by cues present prior to fertilization, and by direction of fertilization Fate mapping: done by staining cells in early stage embryos Fate map of the C. elegans embryo (intestine map shown) "things get freaky, easy" Other
experiments Funky Frog Fetuses:
By manipulating frog embryos at early stages of development, polarity is disturbed (with disturbing ease) Removal of a specific region (the "gray crescent"), leads to an embryo lacking any dorsal structures Transplantation of a specific region (the "dorsal lip") onto another embryo leads to a duplication of the embryo in opposite polarity. Limb Development:
Chicken limb development is dependent upon specific "organizer regions" transplantation of the organizer region (ZPA) leads to limb duplication. What's true for one chordate... Urchin Larvae Overview Plant development continues throughout the plant life cycle

Meristem: Permanently undifferentiated, embryonic tissue.

There is meristematic tissue throughout the plant 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. Primary vs. Secondary Growth Primary growth of the shoot meristem

leaf primordia-
young leaf organ

axillary bud meristem-
will give rise to lateral stems, if
far enough awway from apical bud Primary growth of the root meristem

Apical meristem is in the Zone of Cell Division.
Formation of a lateral root Time Lateral Roots originate from the pericycle, the outermost layer of the vascular cylinder Tissue Structure of young roots 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. Tissue Structure of young stems 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
Plant Tissues Secondary growth of the vascular cambium leads to development of additional layers of xylem & phloem

initially, xylem is produced more rapidly than phloem Once primary growth of stems is complete, only secondary growth occurs.

Vascular cambium-
produces secondary xylem and phloem Wood Production "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

Why does a tree put on more secondary growth every year? Wood is easily the most commercially important plant product Alive
Dead? Dendrochronology The study of tree rings.

Learn all sorts of things.

Pine tree data: wider rings = hotter years

Conclusions? Tissue Structure of leaves This is not anything new for us. But here it is (C3 leaf shown). The sequence of the Arabidopsis genome 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 Parenchymal cells: undifferentiated plant cells We have a better understanding of plant development now than we ever did.

Here are some of the broad strokes Genetics of Plant Development Symmetry & Cell Division Old thought:
Plane of division affected organ form.

New thought:
Plane isn't so important even though these mutants are wacky, the leaves they make look fine 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? However... Pattern Formation Overexpression of the KNOTTED-1 gene in tomato mutants leads to "super compound" leaves compared to the wild type Animal cells differentiate due to lineage based mechanisms (who they are).

Plant cells differentiate due to position based mechanisms (where they are). Pretty flowers? Flowering is under genetic control.

Mutations in flower pattern formation genes lead to abnormalities Any Questions? Any 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? Big Questions Can You 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?
And Away We Go At this point, each cell can still become a whole organism ("totipotency") All "Blue" light micrographs depict sea urchin embryos Frog embryo shown Cork Cambium-
Produces productive bark (periderm) Cleavage in a frog embryo Gastrulation in a sea urchin Gastrulation & Neurulation in a frog
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