Agenda 11/28 Start Development –watch video and do slides Note - during slides take notes when indicated (material.

Agenda 11/28

Start Development –watch video and do slides http://www.youtube.com/watch?v=_22CFCxDUy0

Note - during slides take notes when indicated (material that you didn’t read but you should know/study for quiz)

Homework - • Finish 47.3 notes, concept checks and online

assignment due tomorrow• Quiz Friday - 11,12, 13, 47.3 all fair game (the more you

study, the better off you will be on unit test in 2 weeks)

http://www.youtube.com/watch?v=_22CFCxDUy0



• Development occurs at many points in the life cycle of an animal

• This includes metamorphosis and gamete production, as well as embryonic development

© 2011 Pearson Education, Inc.

Figure 47.2

EMBRYONIC DEVELOPMENTSperm

Adultfrog

Egg

Metamorphosis

Larvalstages

Zygote

Blastula

Gastrula

Tail-budembryo

FE

RT

ILIZ

AT

ION

CLEAVAGE

GASTRULATION

OR

GA

NO

-

GE

NE

SIS

• Although animals display different body plans, they share many basic mechanisms of development and use a common set of regulatory genes

• Biologists use model organisms to study development, chosen for the ease with which they can be studied in the laboratory


Concept 47.1: Fertilization and cleavage initiate embryonic development

• Fertilization is the formation of a diploid zygote from a haploid egg and sperm


Fertilization• Molecules and events at the egg surface play a

crucial role in each step of fertilization– Sperm penetrate the protective layer around the

egg

– Receptors on the egg surface bind to molecules on the sperm surface

– Changes at the egg surface prevent polyspermy, the entry of multiple sperm nuclei into the egg


Cleavage• Fertilization is followed by cleavage, a period of

rapid cell division without growth• Cleavage partitions the cytoplasm of one large cell

into many smaller cells called blastomeres• The solid ball of cells is called a morula• The blastula is a ball of cells with a fluid-filled

cavity called a blastocoel


• Continued cleavage produces the morula.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 47.8b

– Except for mammals, most animals have both eggs and zygotes with a definite polarity.• Thus, the planes of division follow a specific pattern

relative to the poles of the zygote.• Polarity is defined by the heterogeneous distribution

of substances such as mRNA, proteins, and yolk.– Yolk is most concentrated at the vegetal pole and least

concentrated at the animal pole.

• In some animals, the animal pole defines the anterior end of the animal.


• A blastocoel forms within the morula blastula


Fig. 47.8d

Figure 47.6

(a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula

50 m

• Animal embryos complete cleavage when the ratio of material in the nucleus relative to the cytoplasm is sufficiently large


Regulation of Cleavage

• After cleavage, the rate of cell division slows and the normal cell cycle is restored

• Morphogenesis, the process by which cells occupy their appropriate locations, involves

– Gastrulation, the movement of cells from the blastula surface to the interior of the embryo

– Organogenesis, the formation of organs


Concept 47.2: Morphogenesis in animals involves specific changes in

cell shape, position, and survival

Gastrulation• Gastrulation rearranges the cells of a blastula

into a three-layered embryo, called a gastrula


• The three layers produced by gastrulation are called embryonic germ layers

– The ectoderm forms the outer layer

– The endoderm lines the digestive tract

– The mesoderm partly fills the space between the endoderm and ectoderm

• Each germ layer contributes to specific structures in the adult animal


Go to study area online – Ch. 47

• Watch video of sea urchin development

ECTODERM (outer layer of embryo)

MESODERM (middle layer of embryo)

ENDODERM (inner layer of embryo)

• Epidermis of skin and its derivatives (including sweat glands, hair follicles)

• Epithelial lining of digestive tract and associated organs (liver, pancreas)• Epithelial lining of respiratory, excretory, and reproductive tracts and ducts

• Germ cells• Jaws and teeth• Pituitary gland, adrenal medulla• Nervous and sensory systems

• Skeletal and muscular systems• Circulatory and lymphatic systems• Excretory and reproductive systems (except germ cells)• Dermis of skin• Adrenal cortex

• Thymus, thyroid, and parathyroid glands

Figure 47.8

• Gastrulation begins at the vegetal pole of the blastula

• Mesenchyme cells migrate into the blastocoel• The vegetal plate forms from the remaining cells of

the vegetal pole and buckles inward through invagination


Gastrulation in Sea Urchins

• The newly formed cavity is called the archenteron

• This opens through the blastopore, which will become the anus


Animalpole

Blastocoel

Mesenchymecells

Vegetal plateVegetalpole

Blastocoel

Filopodia

Mesenchymecells

Blastopore

Archenteron

50 m

Ectoderm

Mouth

Mesenchyme(mesoderm formsfuture skeleton)

Blastopore

Blastocoel

Archenteron

Digestive tube (endoderm)

Anus (from blastopore)

Key

Future ectodermFuture mesodermFuture endoderm

Figure 47.9

• Frog gastrulation begins when a group of cells on the dorsal side of the blastula begins to invaginate

• This forms a crease along the region where the gray crescent formed

• The part above the crease is called the dorsal lip of the blastopore


Gastrulation in Frogs

• Cells continue to move from the embryo surface into the embryo by involution

• These cells become the endoderm and mesoderm

• Cells on the embryo surface will form the ectoderm


Key

Future ectodermFuture mesodermFuture endoderm

SURFACE VIEW CROSS SECTIONAnimal pole

Vegetal poleEarlygastrula

Blastocoel

Dorsal lip ofblasto-pore

BlastoporeDorsal lip ofblastopore

Blastocoelshrinking

Archenteron

Archenteron

Blastocoelremnant

EctodermMesodermEndoderm

Blastopore

Yolk plugBlastopore

Lategastrula

3

2

1

Figure 47.10

Organogenesis

• During organogenesis, various regions of the germ layers develop into rudimentary organs

• Early in vertebrate organogenesis, the notochord forms from mesoderm, and the neural plate forms from ectoderm


Figure 47.13

Neural folds

1 mm

Neural fold

Neural plate

Notochord

Ectoderm

Mesoderm

Endoderm

Archenteron

(a) Neural plate formation

(b) Neural tube formation

(c) Somites

Neural fold

Neural plate

Neural crest cells

Outer layerof ectoderm

Neural crest cells

Neural tube

Eye Somites Tail bud

SEM

Neural tube

Notochord

Coelom

Neuralcrestcells

Somite

Archenteron(digestivecavity)

1 mm

• The neural plate soon curves inward, forming the neural tube

• The neural tube will become the central nervous system (brain and spinal cord)

NOW – WATCH FROG DEVELOPMENT VIDEO FROM WEBSITE – ALSO FETAL ULTRASOUNDS


• Programmed cell death is also called apoptosis• At various times during development, individual

cells, sets of cells, or whole tissues stop developing and are engulfed by neighboring cells

• For example, many more neurons are produced in developing embryos than will be needed-Extra neurons are removed by apoptosis

• Another example is the morphogenesis of fingers and toes (cells between undergo apoptosis)


Programmed Cell Death

Agenda 11/29• Continue development (slides from 18.4 – this material used to be in 47.3 in

old edition) through bicoid• Take a study break – review/quiz each other on material below

What to study for the quiz:– Cell signaling notes and diagrams in book– Mitosis/Meiosis lab and diagrams– Development notes (Powerpoint posted online) – won’t be anything on quiz

that don’t get through today• Start 47.3 slides – aim to get through fate mapping

• Homework – • Study for quiz tomorrow- 11,12, 13, 47.3 all fair game (the more you study,

the better off you will be on unit test in 2 weeks)

Concept 18.4: A program of differential gene expression leads to the different cell

types in a multicellular organism

• During embryonic development, a fertilized egg gives rise to many different cell types

• Cell types are organized successively into tissues, organs, organ systems, and the whole organism

• Gene expression orchestrates the developmental programs of animals


A Genetic Program for Embryonic Development

• The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis


Figure 18.16

(a) Fertilized eggs of a frog (b) Newly hatched tadpole

1 mm 2 mm

• Cell differentiation is the process by which cells become specialized in structure and function

• The physical processes that give an organism its shape constitute morphogenesis

• Differential gene expression results from genes being regulated differently in each cell type

• Materials in the egg can set up gene regulation that is carried out as cells divide


Cytoplasmic Determinants and Inductive Signals

• An egg’s cytoplasm contains RNA, proteins, and other substances that are distributed unevenly in the unfertilized egg

• Cytoplasmic determinants are maternal substances in the egg that influence early development

• As the zygote divides by mitosis, cells contain different cytoplasmic determinants, which lead to different gene expression


TAKE NOTES

Figure 18.17a(a) Cytoplasmic determinants in the egg

Unfertilized egg

Sperm

Fertilization

Zygote(fertilized egg)

Mitoticcell division

Two-celledembryo

Nucleus

Molecules of twodifferent cytoplasmicdeterminants

SKETCH IN NOTES

• The other important source of developmental information is the environment around the cell, especially signals from nearby embryonic cells

• In the process called induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells

• Thus, interactions between cells induce differentiation of specialized cell types


TAKE NOTES

Figure 18.17b (b) Induction by nearby cells

Early embryo(32 cells)

NUCLEUS

Signaltransductionpathway

Signalreceptor

Signalingmolecule(inducer)

SKETCH IN NOTES


Animation: Cell Signaling

Right-click slide / select “Play”

NICE REVIEW OF CH. 11 CELL SIGNALING

Sequential Regulation of Gene Expression During Cellular

Differentiation• Determination commits a cell to its final fate• Determination precedes differentiation• Cell differentiation is marked by the production of

tissue-specific proteins


TAKE NOTES

Pattern Formation: Setting Up the Body Plan

• Pattern formation is the development of a spatial organization of tissues and organs

• In animals, pattern formation begins with the establishment of the major axes

• Positional information, the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells


KNOW THESE VOCAB WORDS –THEY SHOULD BE IN YOUR CORNELL NOTES

Axis Establishment• Maternal effect genes encode for cytoplasmic

determinants that initially establish the axes of the body of Drosophila

• These maternal effect genes are also called egg-polarity genes because they control orientation of the egg and consequently the fly



Animation: Development of Head-Tail Axis in Fruit Flies

Right-click slide / select “Play”

• One maternal effect gene, the bicoid gene, affects the front half of the body

• An embryo whose mother has no functional bicoid gene lacks the front half of its body and has duplicate posterior structures at both ends

Bicoid: A Morphogen Determining Head Structures


Figure 18.21

Head Tail

Tail Tail

Wild-type larva

Mutant larva (bicoid)

250 m

T1 T2 T3A1 A2 A3 A4 A5 A6

A7A8

A8A7A6A7

A8

• This phenotype suggests that the product of the mother’s bicoid gene is concentrated at the future anterior end

• This hypothesis is an example of the morphogen gradient hypothesis, in which gradients of substances called morphogens establish an embryo’s axes and other features


TAKE NOTES – KNOW BICOID EXAMPLE

Figure 18.22

Bicoid mRNA in matureunfertilized egg

Bicoid mRNA in matureunfertilized egg

Fertilization,translation ofbicoid mRNA

Anterior end100 m

Bicoid protein inearly embryo

Bicoid protein inearly embryo

RESULTS

• The bicoid research is important for three reasons– It identified a specific protein required for some

early steps in pattern formation

– It increased understanding of the mother’s role in embryo development

– It demonstrated a key developmental principle that a gradient of molecules can determine polarity and position in the embryo


PAUSE HERE FOR STUDY BREAK

Concept 47.3: Cytoplasmic determinants and inductive signals contribute to cell fate specification

• Determination is the term used to describe the process by which a cell or group of cells becomes committed to a particular fate

• Differentiation refers to the resulting specialization in structure and function


Fate Mapping• Fate maps are diagrams showing organs and

other structures that arise from each region of an embryo

• Classic studies using frogs indicated that cell lineage in germ layers is traceable to blastula cells


Epidermis EpidermisCentralnervoussystemNotochord

Mesoderm

Endoderm

Blastula Neural tube stage(transverse section)

(a) Fate map of a frog embryo

64-cell embryos

Blastomeresinjected with dye

Larvae

(b) Cell lineage analysis in a tunicate

Figure 47.17

• Later studies of C. elegans used the ablation (destruction) of single cells to determine the structures that normally arise from each cell

• The researchers were able to determine the lineage of each of the 959 somatic cells in the worm


First cell divisionZygote

HatchingTim

e a

fter

fer

tiliz

ati

on

(h

ou

rs)

Intestine

Intestine

MouthEggs Vulva

Anus

1.2 mmANTERIOR POSTERIOR

Nervoussystem,outer skin,muscula-ture

Muscula-ture, gonads

Outer skin,nervous system

Germ line(futuregametes)

Musculature

10

0Figure 47.18

• Germ cells are the specialized cells that give rise to sperm or eggs

• Complexes of RNA and protein are involved in the specification of germ cell fate

• In C. elegans, such complexes are called P granules, persist throughout development, and can be detected in germ cells of the adult worm

• P granules act as cytoplasmic determinants, fixing germ cell fate at the earliest stage of development


Figure 47.20

Newly fertilized egg

Zygote prior to first division

Two-cell embryo

Four-cell embryo

20 m

2

1

3

4

Figure 47.19

100 m

Axis Formation• A body plan with bilateral symmetry is found

across a range of animals• This body plan exhibits asymmetry across the

dorsal-ventral and anterior-posterior axes• The right-left axis is largely symmetrical


• The anterior-posterior axis of the frog embryo is determined during oogenesis

• The animal-vegetal asymmetry indicates where the anterior-posterior axis forms (animal is embryo, vegetal is yolk)

• The dorsal-ventral axis is not determined until fertilization


• Upon fusion of the egg and sperm, the egg surface rotates with respect to the inner cytoplasm

• This cortical rotation brings molecules from one area of the inner cytoplasm of the animal hemisphere to interact with molecules in the vegetal cortex

• This leads to expression of dorsal- and ventral-specific gene expression


Dorsal

Right

Anterior Posterior

VentralLeft

(a) The three axes of the fully developed embryo

(b) Establishing the axes

Animalhemisphere

Vegetalhemisphere

Animal pole

Vegetal pole

Point ofspermnucleusentry

Gray crescent

Pigmentedcortex

Futuredorsalside

First cleavage

Figure 47.21

• In chicks, gravity is involved in establishing the anterior-posterior axis

• Later, pH differences between the two sides of the blastoderm establish the dorsal-ventral axis

• In mammals, experiments suggest that orientation of the egg and sperm nuclei before fusion may help establish embryonic axes


Restricting Developmental Potential

• Hans Spemann performed experiments to determine a cell’s developmental potential (range of structures to which it can give rise)

• Embryonic fates are affected by distribution of determinants and the pattern of cleavage

• The first two blastomeres of the frog embryo are totipotent (can develop into all the possible cell types)


Control egg(dorsal view)

1a 1b

Graycrescent

Controlgroup

Experimentalgroup

Experimental egg(side view)

Graycrescent

EXPERIMENT

Thread

Figure 47.22-1

Control egg(dorsal view)

2

1a 1b

Graycrescent

Controlgroup

Experimentalgroup

Experimental egg(side view)

Graycrescent

Thread

Normal NormalBelly piece

EXPERIMENT

RESULTS

Figure 47.22-2

• In mammals, embryonic cells remain totipotent until the 8-cell stage, much longer than other organisms

• Progressive restriction of developmental potential is a general feature of development in all animals

• In general tissue-specific fates of cells are fixed by the late gastrula stage


Cell Fate Determination and Pattern Formation by Inductive Signals

• As embryonic cells acquire distinct fates, they influence each other’s fates by induction


The “Organizer” of Spemann and Mangold

• Spemann and Mangold transplanted tissues between early gastrulas and found that the transplanted dorsal lip triggered a second gastrulation in the host

• The dorsal lip functions as an organizer of the embryo body plan, inducing changes in surrounding tissues to form notochord, neural tube, and so on


Figure 47.23

Dorsal lip ofblastopore

Pigmentedgastrula

(donor embryo)Nonpigmented

gastrula(recipient embryo)

Primary embryo

Secondary (induced) embryo

Primary structures:Neural tubeNotochord

Secondary structures:Notochord (pigmented cells)Neural tube(mostly nonpigmented cells)

EXPERIMENT RESULTS

Formation of the Vertebrate Limb • Inductive signals play a major role in pattern

formation, development of spatial organization• The molecular cues that control pattern formation

are called positional information• This information tells a cell where it is with respect

to the body axes• It determines how the cell and its descendents

respond to future molecular signals


• The wings and legs of chicks, like all vertebrate limbs, begin as bumps of tissue called limb buds


Figure 47.24

Limb buds

50 m

AnteriorLimb bud

AER

ZPA

Posterior

Apicalectodermalridge (AER)

(a) Organizer regions (b) Wing of chick embryo

Digits

Anterior

Proximal

Dorsal

Posterior

Ventral

Distal

2

34

• The embryonic cells in a limb bud respond to positional information indicating location along three axes

– Proximal-distal axis

– Anterior-posterior axis

– Dorsal-ventral axis


• One limb bud–regulating region is the apical ectodermal ridge (AER)

• The AER is thickened ectoderm at the bud’s tip• The second region is the zone of polarizing

activity (ZPA)• The ZPA is mesodermal tissue under the

ectoderm where the posterior side of the bud is attached to the body


• Tissue transplantation experiments support the hypothesis that the ZPA produces an inductive signal that conveys positional information indicating “posterior”


Figure 47.25

Donorlimbbud

Hostlimbbud

ZPA

Anterior

Posterior

New ZPA

4

4

3

3

2 2

EXPERIMENT

RESULTS

• Sonic hedgehog is an inductive signal for anterior/posterior limb development – gradient from ZPA

• Hox genes also play roles during limb pattern formation

© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Cilia and Cell Fate• Ciliary function is essential for proper specification of cell

fate in the human embryo• Motile cilia play roles in left-right specification (always

sweep fluid to the left, creating slight asymmetry of morphogens on left-right axis)

• Monocilia (nonmotile cilia) are on every cell and act as antenna to receive signal proteins (such as Sonic hedgehog) – play roles in normal kidney development


Figure 47.26

Lungs

Heart

Liver

Spleen

Stomach

Large intestine

Normal locationof internal organs

Location insitus inversus

Caused by defect in motile cilia in a particular part of the embryo

Agenda 11/28 Start Development –watch video and do slides Note - during slides take notes when indicated (material.

Documents

pearson education

regulation of cleavage

cleavage fertilization

d slide

b slide

benjamin cummings slide

growth cleavage

continued cleavage