Zoology Exam 3 (Mine)

Hans Spemann and Hilde Mangold

Tissue induction- salamander embryos

-Take a dorsal lip from a salamander gastrula, implant it in a host salamander = grows new salamander

When did Spemann win the Nobel prize?

1935

Why couldn’t Mangold receive the Nobel prize?

Burns from a home gas heater accident

—Fun fact: Rosalind Franklin couldn’t get her Nobel prize because she died from cancer from irradiation

How did we close the gap of understanding in developmental biology?

Fusion of genetics, evolution, and functional molecular biology

Ernst Haeckel

Came up with the DUMB developmental biology idea that we went thru different animals before becoming a human baby in the womb

Historical ideas of how babies are made - Preformation

Entire organism was a miniaturized version w/in sperm or egg

Historical ideas of how babies are made - Epigenesis

(Origin upon or after) - Egg contains building material activated by sperm

Cellular number and diversity arises

sequentially

A cell’s fate is determined by one of 2 processes

-Specification (like picking a major for college)

-Induction (like you already took all the requirements…you are in to deep to change

• Usually IRREVERSIBLE

Morphogenetic determinants

-Transcription

-Induction factors

-Direct activation

-Repression of genes

• MUST HAPPEN at correct times

At times fertilization can occur when?

Before the oocyte has undergone meiosis

Male and female gametes unite to form

Zygote

• combination of male and female genes

• restores diploid chromosomal status

In regards to oocyte maturity, what is HIGHLY variable?

Timing of fertilization

Is sperm always required for egg activation?

NO

Species specific recognition proteins

PREVENT fertilization by another species (post-mating, prezygotic)

• USEFUL for gametes in water

Prevention of polyspermy

-Polyspermy: n+n+n+…=Xn (NOT GOOD)

• Normal: n+n = 2n

Fast block

Electrical potential charge change in the egg membrane

Slow block

Cortisol reaction, thousands of enzyme capsules release contents between the egg membrane and vitellene envelope

• Creates an osmotic gradient, water rushes in, sperm washed away

  • Causes the vitellene membrane to harden and physically block sperm

What do we use sea urchins?

-Easy to find, cheap

-Fertilization external - easy in the lab

-Embryo is transparent - easy to see development

-Very historic - Aristotle used them

Blastomeres

-Small, maneuverable cells

• NO growth, just a big mass dividing into normal sized cells

Polarity established

-Animal pole - dark side

-Vegetal pole - light side

Frogs (Xenopus) were used for

Pregnancy tests

-Hormones of a pregnant woman made the female frogs lay eggs

Yolk distribution

-Isolecithal

-Mesolecithal

-Telolecithal

-Centrolecithal

Isolecithal

-VERY LITTLE yolk, evenly distributed

• Ex: Urchin

Mesolecithal

-MODERATE amount of yolk at vegetal pole (Light side)

• Ex: Xenopus

Telolecithal

-LOTS of yolk at vegetal pole

• Ex: Zebrafish

Centrolecithal

-LARGE, centrally located yolk

• Ex: Insects

Meroblastic cleavage

-Lots of yolk sitting on top of undivided yolk

• Ex: Chicken egg

Holoblastic cleavage

-Cleavage furrows extends completely throughout egg

Direct developement

-Embryo to miniature adult

• Fish/sharks

Indirect development

-Multiple developmental stages

• Ex: human

Matrotrorphy

-Mother nourishes developing embryo

• Found in both direct and indirect development

Blastula

-A cluster of cells

• Usually hollow → space called blastocoel

• Process called blastulation

• ONE layer of germ cells (one tissue layer)

Gastrulation

Conversion of the spherical blastula into a 2 or 3 layered embryo

• Monoblastic to triploblastic

Archenteron

-Internal pouch formed in gastrulation

Blastopore

-Opening to the archenteron

Triploblastic

-3 primary germ cell layers

• Ectoderm

• Mesoderm

• Endoderm

Ectoderm

- Most exterior

• Becomes integument and nervous system

Endoderm

-Most of the GI tract, and internal organs

Mesoderm

-Most connective tissues, fluids, and muscles

Coelom

-Body cavity completely surrounded by the mesoderm

• Formed by one of two methods

  • Schizocoely

  • Enterocoely

• When formation is complete → body has 3 germ layers and 2 cavities (gut and coelom)

When body formation is complete, coelomates have

-3 germ layers and 2 body cavities (gut and coelom)

Body cavities

-Coelomates

-Pseudocoelomates

-Acoelomates

LOOK AT LAB MANUAL FOR MORE INFO

Diersch

Sea urchin grinding and shaking

Experiments in developmental biology by Diersch and Spemann

-Led to the idea that every somatic cell contains the full genetic instructions for making an organism

-Cloning cell lines and whole organisms

• Stem cell research

Dolly the sheep

-First cloned mammal

• Electricity simulates action potential of a cell

When and where was Dolly the sheep cloned?

1996 by scientists in Scotland

Induction

Capacity of some cells to evoke a developmental response in other cells

-Two types:

• Primary induction

• Secondary induction

Primary induction

From the dorsal lip (ectoderm) during gastrulation

-Last real chance to make a whole new organism

• Gastrulation is REALLY important

Secondary induction

Other cell types originate later from other induction events

Primitive streak

Center of early embryonic growth in many animals

Synctium

A single membrane surrounds multiple nuclei

What is synctial specification useful for?

-USEFUL for studying developmental biology

• Genetic changes among nuclei in same cell

Speciation of body axes

-Front/back (anteroposterior or top/bottom) -

-Left/right

-Back/front (dorsoventral)

Very conserved genes that forms pattern formation

-Hox

-Sonic Hedgehog

Sonic Hedgehog gene

Timing (when to make the body parts)

Hox genes

Development and differential of body parts

• MOST CONSERVED GENES EVER!

• SAME genes that controls making a fly's

  head, makes your head

Segmentation (metamerism)

Division of the body into distinct segments

-Gap genes: big segments

-Pair-rule genes: divide the big segments into repeated segments

Developmental patterns

-Protostome: blastopore forms mouth

-Deuterostome: blastopore forms anus

• Determinate (Mosaic)

  • HIGHLY influenced by development of cytoplasm

  • What makes twins and so on to be possible

• Indeterminate (Regulative)

Questions for Developmental patterns

-As embryo cleaves, do cells form a spiral or radial pattern

-Cytoplasmic or conditional specification?

-Blastopore mouth or anus?

-Schizocoely or enterocoely?

Coelom formation

-Schizocoely

-Enterocoely

Schizocoely

-Mesodermal band of tissue around gut forms before coelom

-Splits mesodermal tissue

-Coelom forms by ingression of mesoderm

• Protostomes (coelom forms from splitting of the mesoderm)

  • Ex: molluscs, annelids, arthropods

Enterocoely

-Mesoderm forms two pockets of tissue, on each side, that eventually meet

-Coelom and mesoderm form at the time

• Coelom forms by out-pocketing of primitive gut

  • Ex: echinopods, chordates

Variations in cleavage

-Spiral

-Radial

-Bilateral cleavage

-Rotational cleavage

-Discoidal

Spiral cleavage

Blastomeres cleave obliquely at 45 degree angles

• RESULTS: Cells somewhat offset from their parent cell

Radial cleavage

Blastomeres cleave evenly in relation to each other

• RESULTS: A symmetrical looking embryo

Bilateral cleavage

Cleavage on one side is a mirror image of the other

• Ex: Ascidians

Rotational cleavage

Blastomeres divide at different times and some early blastomeres divide perpendicularly to others

• Ex: mammals

Discoidal

Cleavage restricted to a small disk of cytoplasm on top of yolk

• Ex: reptiles, most fish

Are all bilaterally symmetrical animals fundamentally similar?

Probably

Can we infer the anatomy of extinct ancestral species from developmental genes?

NO

Is it possible that simple changes in developmental genes account for the wide diversity of organisms?

Yes/Probably

What does homology really mean in the context of developmental biology

Not known…really hard to figure out

Which animals embryos’ form in a membranous sac, the amnion?

Reptiles and mammals

Four Extraembryonic membranes

-Amnion: provides aqueous environment

• Fluid the baby resides in

-Chorion: final membrane for enclosure

• Produces the hormone (that only pregnant women produce) but it

  takes several days to do this

  after contraception

-Allantois: repository for wastes

-Yolk sac: provides nourishment, very ancient

WITHIN THE EMBRYO

THEY FORM THE AMNIOTIC EGG

3 groups of mammals

-Monotremes (platypus, echidna)

• Lays eggs and milk leaks thru skin

-Marsupials (possums, kangaroos)

-Placentals (everyone else, 94% of species)

Placenta

Modified version of an amniotic egg

• Involves substantial modification to the uterus.

Why isn’t the placenta rejected by the mother’s immune system?

It produces proteins and lymphocytes that suppress mother’s immune system

Allantois becomes incorporated into

The umbilical cord

Placental development

-Germinal period

-Embryonic period

-Fetal period

Germinal period

In humans, two weeks long, EMBRYO VERY RESISTENT to outside influence

Embryonic period

Next eight weeks, all major organs forming, EMBRYO EXTREMELY SENSITIVE to outside influence

• Morning sickness

• If you drink alcohol a lot during this time, baby WILL DEVELOP FETAL ALCOHOL SYNDROME

Fetal period

After two months, mostly growth and continued development

Ectoderm is responsible for

The nervous system

Ectoderm thickens to form

-Neural plate above notochord,

-Edges join

-Form neural tube.

Nerve cells grow and develop from

Cues exterior to the cell itself

• They follow “road signs.”

Endoderm forms

The digestive system

Alimentary canal emerges from

the primitive gut

Lungs, liver, pancreas emerge from

foregut

Gill arches and their derivatives (jaws, ears) emerge from

endoderm

Development of Mesoderm

-Forms muscles (Abs in adults)

• Arise from repeated segments called somites

-Forms muscular organs such as heart

Primary organizer

Region of dorsal lip of gastrula’s blastopore responsible for primary induction (last chance to develop a complete organism) event leading to complete embryo

Phylum Gnathostomulida

-Greek: gnathos (mouth) and stoma (opening)

-Small, delicate wormlike animals.

-Live in fine sediments near coastlines, but can tolerate deep water.

-Can glide and swim.

-Have monociliated epidermal cells.

-Acoelomate

-NO circulatory system

-Jaws that lead to a simple, blind gut

-Internal, cross fertilization

JAW WORMS

Phylum Micrognathozoa

-Monotypic, Limnognathia maerski

-Discovered in 1994, described in 2000!

-THREE pairs of jaws

-Only female reproductive organs, poorly understood

-MOVEMENT BY CILIA

-Unique ventral ciliary pad that produces glue

-Live in sediment

Phylum Rotifera

-Latin: rota (wheel) and fera (bearing)

-Unique organ: Corona (wheel organ)

-LOTS OF VARIATION in life history traits

-Anhydrobiosis: Some can desiccate and live for years