Agenda 11/28 Start Development –watch video and do slides

Agenda 11/28 Start Development –watch video and do slides
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)

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. 2

EMBRYONIC DEVELOPMENT Sperm
Figure 47.2 EMBRYONIC DEVELOPMENT Sperm Zygote Adult frog Egg FERTILIZATION CLEAVAGE Metamorphosis Blastula GASTRULATION Figure 47.2 Developmental events in the life cycle of a frog. ORGANO- GENESIS Larval stages Gastrula Tail-bud embryo 3

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 © 2011 Pearson Education, Inc. 4

Concept 47.1: Fertilization and cleavage initiate embryonic development
Fertilization is the formation of a diploid zygote from a haploid egg and sperm © 2011 Pearson Education, Inc. 5

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 © 2011 Pearson Education, Inc. 6

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 © 2011 Pearson Education, Inc. 7

Continued cleavage produces the morula.
Fig. 47.8b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

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

A blastocoel forms within the morula  blastula
Fig. 47.8d Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

(a) Fertilized egg (b) Four-cell stage (c) Early blastula
Figure 47.6 50 m (a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula Figure 47.6 Cleavage in an echinoderm embryo. 11

Regulation of Cleavage
Animal embryos complete cleavage when the ratio of material in the nucleus relative to the cytoplasm is sufficiently large © 2011 Pearson Education, Inc. 12

Concept 47.2: Morphogenesis in animals involves specific changes in cell shape, position, and survival 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 © 2011 Pearson Education, Inc. 13

Each germ layer contributes to specific structures in the adult animal
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 © 2011 Pearson Education, Inc. 15

Go to study area online – Ch. 47
Watch video of sea urchin development

ECTODERM (outer layer of embryo)
Figure 47.8 ECTODERM (outer layer of embryo) • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Nervous and sensory systems • Pituitary gland, adrenal medulla • Jaws and teeth • Germ cells MESODERM (middle layer of embryo) • Skeletal and muscular systems • Circulatory and lymphatic systems • Excretory and reproductive systems (except germ cells) • Dermis of skin • Adrenal cortex Figure 47.8 Major derivatives of the three embryonic germ layers in vertebrates. ENDODERM (inner layer of embryo) • Epithelial lining of digestive tract and associated organs (liver, pancreas) • Epithelial lining of respiratory, excretory, and reproductive tracts and ducts • Thymus, thyroid, and parathyroid glands 17

Gastrulation in Sea Urchins
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 © 2011 Pearson Education, Inc. 18

The newly formed cavity is called the archenteron
This opens through the blastopore, which will become the anus © 2011 Pearson Education, Inc. 19

Figure 47.9 Animal pole Blastocoel Mesenchyme cells Vegetal plate
Vegetal pole Blastocoel Filopodia Mesenchyme cells Archenteron Blastopore Figure 47.9 Gastrulation in a sea urchin embryo. 50 m Blastocoel Ectoderm Archenteron Key Blastopore Mouth Future ectoderm Mesenchyme (mesoderm forms future skeleton) Digestive tube (endoderm) Future mesoderm Anus (from blastopore) Future endoderm 20

Gastrulation in Frogs 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 © 2011 Pearson Education, Inc. 21

These cells become the endoderm and mesoderm
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 © 2011 Pearson Education, Inc. 22

Figure 47.10 SURFACE VIEW CROSS SECTION Animal pole 1 Blastocoel
Dorsal lip of blastopore Dorsal lip of blastopore Blastopore Early gastrula Vegetal pole 2 Blastocoel shrinking Archenteron Figure Gastrulation in a frog embryo. Ectoderm 3 Blastocoel remnant Mesoderm Endoderm Key Future ectoderm Blastopore Future mesoderm Late gastrula Yolk plug Archenteron Blastopore Future endoderm 23

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 © 2011 Pearson Education, Inc. 24

Figure 47.13 Neural folds Eye Somites Tail bud Neural fold
Neural plate SEM 1 mm 1 mm Neural tube Neural crest cells Neural fold Neural plate Notochord Neural crest cells Coelom Notochord Ectoderm Somite Figure Neurulation in a frog embryo. Mesoderm Outer layer of ectoderm Archenteron (digestive cavity) Endoderm Neural crest cells (c) Somites Archenteron (a) Neural plate formation Neural tube (b) Neural tube formation 25

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 © 2011 Pearson Education, Inc. 26

Programmed Cell Death 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) © 2011 Pearson Education, Inc. 27

Apoptosis (Cell suicide) and Normal Development
A built-in cell suicide mechanism is essential to development in all animals. Similarities between the apoptosis genes in mammals and nematodes indicate that the basic mechanism evolved early in animal evolution. The timely activation of apoptosis proteins in some cells functions during normal development and growth in both embryos and adults. It is part of the normal development of the nervous system, normal operation of the immune system, and for normal morphogenesis of human hands and feet. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Problems with the cell suicide mechanism may have health consequences, ranging from minor to serious. Failure of normal cell death during morphogenesis of the hands and feet can result in webbed fingers and toes. Researchers are also investigating the possibility that certain degenerative diseases of the nervous system result from inappropriate activation of the apoptosis genes. Others are investigating the possibility that some cancers result from a failure of cell suicide which normally occurs if the cell has suffered irreparable damage, especially DNA damage.

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)

© 2011 Pearson Education, Inc.
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 © 2011 Pearson Education, Inc. 31

A Genetic Program for Embryonic Development
The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis © 2011 Pearson Education, Inc. 32

Added from later powerpoint
Genes and Development Differential gene expression leads to different cell types in multicellular organisms Zygote undergoes transformation through 3 interrelated cell processes Cell division – mitosis increases # of cells Cell differentiation – cells become specialized in structure and function Morphogenesis – organization of cells into tissues and organs What are the terms that describe an embryo going through these stages? (Remember Ch. 47)

Added from later powerpoint
Fig. 21.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

(a) Fertilized eggs of a frog (b) Newly hatched tadpole
Figure 18.16 Figure From fertilized egg to animal: What a difference four days makes. 1 mm 2 mm (a) Fertilized eggs of a frog (b) Newly hatched tadpole 35

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 © 2011 Pearson Education, Inc. 36

Cytoplasmic Determinants and Inductive Signals
TAKE NOTES 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 © 2011 Pearson Education, Inc. 37

SKETCH IN NOTES (a) Cytoplasmic determinants in the egg
Figure 18.17a (a) Cytoplasmic determinants in the egg Unfertilized egg SKETCH IN NOTES Sperm Nucleus Fertilization Molecules of two different cytoplasmic determinants Zygote (fertilized egg) Figure Sources of developmental information for the early embryo. Mitotic cell division Two-celled embryo 38

TAKE 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 © 2011 Pearson Education, Inc. 39

SKETCH IN NOTES (b) Induction by nearby cells Early embryo (32 cells)
Figure 18.17b (b) Induction by nearby cells SKETCH IN NOTES Early embryo (32 cells) NUCLEUS Signal transduction pathway Figure Sources of developmental information for the early embryo. Signal receptor Signaling molecule (inducer) 40

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 © 2011 Pearson Education, Inc. 42

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 © 2011 Pearson Education, Inc. 43

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 © 2011 Pearson Education, Inc. 44

Bicoid: A Morphogen Determining Head Structures 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 © 2011 Pearson Education, Inc. 46

Head Tail Wild-type larva 250 m Tail Tail Mutant larva (bicoid)
Figure 18.21 Head Tail A8 T1 T2 T3 A7 A6 A1 A5 A2 A4 A3 Wild-type larva 250 m Tail Tail Figure Effect of the bicoid gene on Drosophila development. A8 A8 A7 A6 A7 Mutant larva (bicoid) 47

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 © 2011 Pearson Education, Inc. 48

Fertilization, translation of bicoid mRNA
Figure 18.22 RESULTS 100 m Anterior end Fertilization, translation of bicoid mRNA Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo Figure Inquiry: Is Bicoid a morphogen that determines the anterior end of a fruit fly? Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo 49

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 © 2011 Pearson Education, Inc. 50

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 © 2011 Pearson Education, Inc. 51

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 © 2011 Pearson Education, Inc. 52

Blastomeres injected with dye
Figure 47.17 Epidermis Epidermis Central nervous system Notochord Mesoderm Endoderm Blastula Neural tube stage (transverse section) (a) Fate map of a frog embryo 64-cell embryos Figure Fate mapping for two chordates. Blastomeres injected with dye Larvae (b) Cell lineage analysis in a tunicate 53

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 © 2011 Pearson Education, Inc. 54

Time after fertilization (hours)
Figure 47.18 Zygote First cell division Nervous system, outer skin, musculature Muscula- ture, gonads Outer skin, nervous system Germ line (future gametes) Time after fertilization (hours) Musculature 10 Hatching Intestine Figure Cell lineage in Caenorhabditis elegans. Intestine Anus Mouth Eggs Vulva ANTERIOR POSTERIOR 1.2 mm 55

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 © 2011 Pearson Education, Inc. 56

Zygote prior to first division
Figure 47.20 20 m 1 Newly fertilized egg 2 Zygote prior to first division Figure Partitioning of P granules during C. elegans development. 3 Two-cell embryo 4 Four-cell embryo 57

Figure 47.19 100 m Figure Determination of germ cell fate in C. elegans. 58

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 © 2011 Pearson Education, Inc. 59

The dorsal-ventral axis is not determined until fertilization
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 © 2011 Pearson Education, Inc. 60

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 © 2011 Pearson Education, Inc. 61

(a) The three axes of the fully developed embryo
Figure 47.21 Dorsal Right Anterior Posterior Left Ventral (a) The three axes of the fully developed embryo Animal pole First cleavage Animal hemisphere Pigmented cortex Point of sperm nucleus entry Figure The body axes and their establishment in an amphibian. Future dorsal side Vegetal hemisphere Gray crescent Vegetal pole (b) Establishing the axes 62

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 © 2011 Pearson Education, Inc. 63

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) © 2011 Pearson Education, Inc. 64

Experimental egg (side view)
Figure EXPERIMENT Control egg (dorsal view) Experimental egg (side view) 1a Control group 1b Experimental group Gray crescent Gray crescent Thread Figure Inquiry: How does distribution of the gray crescent affect the developmental potential of the first two daughter cells? 65

Experimental egg (side view)
Figure EXPERIMENT Control egg (dorsal view) Experimental egg (side view) 1a Control group 1b Experimental group Gray crescent Gray crescent Thread Figure Inquiry: How does distribution of the gray crescent affect the developmental potential of the first two daughter cells? 2 RESULTS Normal Belly piece Normal 66

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 © 2011 Pearson Education, Inc. 67

Cell Fate Determination and Pattern Formation by Inductive Signals
As embryonic cells acquire distinct fates, they influence each other’s fates by induction © 2011 Pearson Education, Inc. 68

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 © 2011 Pearson Education, Inc. 69

Dorsal lip of blastopore Primary embryo
Figure 47.23 EXPERIMENT RESULTS Dorsal lip of blastopore Primary embryo Secondary (induced) embryo Pigmented gastrula (donor embryo) Primary structures: Nonpigmented gastrula (recipient embryo) Neural tube Notochord Figure Inquiry: Can the dorsal lip of the blastopore induce cells in another part of the amphibian embryo to change their developmental fate? Secondary structures: Notochord (pigmented cells) Neural tube (mostly nonpigmented cells) 70

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 © 2011 Pearson Education, Inc. 71

The wings and legs of chicks, like all vertebrate limbs, begin as bumps of tissue called limb buds
© 2011 Pearson Education, Inc. 72

Figure 47.24 Anterior Limb bud AER ZPA Limb buds Posterior 2 50 m
Digits Apical ectodermal ridge (AER) 3 4 Anterior Figure Vertebrate limb development. Ventral Proximal Distal Dorsal Posterior (a) Organizer regions (b) Wing of chick embryo 73

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 © 2011 Pearson Education, Inc. 74

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 © 2011 Pearson Education, Inc. 75

EXPERIMENT Anterior New ZPA Donor limb bud Host limb bud ZPA Posterior
Figure 47.25 EXPERIMENT Anterior New ZPA Donor limb bud Host limb bud ZPA Posterior RESULTS 4 Figure Inquiry: What role does the zone of polarizing activity (ZPA) play in limb pattern formation in vertebrates? 3 2 2 3 4 77

Hox genes also play roles during limb pattern formation
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. 78

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 © 2011 Pearson Education, Inc. 79

Normal location of internal organs Location in situs inversus
Caused by defect in motile cilia in a particular part of the embryo Figure 47.26 Lungs Heart Liver Spleen Stomach Figure Situs inversus, a reversal of normal left-right asymmetry in the chest and abdomen. Large intestine Normal location of internal organs Location in situs inversus 80

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