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93 Cards in this Set
- Front
- Back
What drives gastrulation? |
Morphogenesis |
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What is morphogenesis characterized by? |
Changes at the cell level |
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What changes occur during morphogenesis? |
Cell adhesion (or the cell's affinities for each other)
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What changes occur during gastrulation? |
Tissues are produced Germ layers are determined and regionalized The axes of the organism are detertmined |
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What happens prior to gastrulation? |
The midblastula transition occurs. |
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What changes occur during the midblastula transition? |
1. There is a change in the frequency of cell division. Cells acquire a gap/growth phase. 2. There is a change in gene expression known as the maternal-zygotic transition. |
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When does the maternal-zygotic transition occur and what changes take place during it? |
It occurs prior to gasrulation. The embryo takes over driving its own transcription (zygotic gene expression) And the maternal determinants are no longer used. |
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Who was Johannes Holtfreter and why is he important? |
He was a German embryologist. Who... Developed numerous cell-culture techniques, Studied axes specification in the frog, Studied neural development, and Studied cell-cell interactions during gastrulation. |
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What was tested and discovered in the Holtfreter and Townes experiments? |
Used post-gastrulation amphibian embryos. Dissociation and regression of tissues: 1. Separated and recombined ectoderm and endoderm. Cells had a high affinity for cells of the same type and repelled each other. 2.Dissociated and reaggregated two ectodermal derivatives: epidermal and neural cells. Found that neural cells had a higher affinity for each other than did epidermal cells. Both cell types also had a positive affinity for each other. Variety of Germ Layer Recombinations Strongest affinity to weakest affinity: neural ectoderm, mesoderm, endoderm, epidermal ectoderm |
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Generalizations about tissues from Holtfreter and Townes experiments |
There exist strong affinities between cells within a tissue. The weakest interfaces exist between cells of different tissues. |
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Why is Malcolm Steinberg important? |
He examined the cell affinities for a variety of adult tissues, and found that these tissues sorted in relation to each other Created the differential adhesion hypothesis. |
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Differential adhesion hypothesis |
Different cell types have different adhesion properties Cells will sort according to their strength of adhesion They will organize themselves in such a way as to achieve the greatest thermodynamic stability |
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What determines cell affinities? |
Cell adhesion molecules (CAMs) |
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What 2 properties of cell adhesion molecules (CAMs) contribute to the affinities between cells? |
Qualitative properties: Different cells have different CAMs Quantitative properties: The number of a single type of CAM on a cell as well as the number of types of CAMs on a cell |
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What structures help alter the cytoskeleton |
Microfilaments |
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What do microfilaments do to help alter the cytoskeleton |
Cleave cells by acting as a contractile ring Change cell shape through apical constriction via a contractile actin network Migrate a single cell by creating lamellipodium via actin/myosin bundles |
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Types of morphogenic movement |
1. Invagination 2. Involution 3. Ingression 4. Delamination 5. Intercalation 6. Epiboly |
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Describe invagination |
an in-pocketing creates a sheath invaginating cells undergo apical constriction |
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Describe involution |
cells spiral under |
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Describe ingression |
Single cells undergo epithelial to mesenchyme transition or mesenchyme to epithelial transition.
Cells sort of drip into new tissue |
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Describe delamination |
Epithelial to mesenchyme and mesenchyme to epithelial transitions, one after the other. Creates 2 layers of tissue. |
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Describe intercalations |
Multiple planes of epithelium merge to create a single plane |
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Describe radial intercalation |
cell planes on top of each other merge vertically to create one plane |
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Describe medio-lateral intercalation / convergent extension |
cell planes next to each other merge laterally to create one line of cells elongate tissue in a line |
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Describe epiboly |
Cells spreading One of 3 ways: radial intercalation thinning of cells proliferation |
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Steps of gastrulation in sea urchins |
1. Ingression of primary mesenchyme 2. Invagination of endoderm 3a. Ingression of secondary mesenchyme 3b. Elongation of gut rudiment 4. Mouth formation 5. Differentiation of tissues |
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What happens during ingression of primary mesenchyme in sea urchin gastrulation? |
The mesoderm ingresses The primary mesenchyme will migrate to the vegetal and lateral regions of the blastocoel Produce filopodia to detect their environment |
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What happens during invagination of endoderm in sea urchin gastrulation? |
the endoderm invaginates to form the gut rudiment |
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What happens during ingression of secondary mesenchyme in sea urchin gastrulation? |
Mesoderm Ingresses off the end of the gut rudiment |
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What happens during elongation of the gut rudiment in sea urchin gastrulation? |
The gut rudiment narrows and elongates via convergent extension of secondary mesenchyme. Filopodia act as anchors; they generate tension that drives elongation. |
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What happens during mouth formation in sea urchin gastrulation? |
Secondary mesenchyme drags the gut to the lateral margins The gut fuses with the lateral wall (The sea urchin is a deuterostome; the invagination from the blastocoel forms the anus) |
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What happens during the differentiation of tissues in sea urchin gastrulation? |
1. The gut divides into 3 parts: -foregut- esophagus -midgut- stomach -hindgut- intestine 2. The mesenchyme differentiates: -Primary mesenchyme- skeletal rods -Secondary mesenchyme- coelom, immunocytes, pigment, muscle --coelom forms via enterocoely |
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Where does involution of amphibian gastrulation start and what type of cells form there? |
Involution begins at the dorsal marginal zone Bottle cells mark the site of involution |
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Who is Ray Keller and why is he important? |
He is a developmental biologist (at the University of Virginia) Studies neural and mesodermal morphogenesis He performed explant studies to show autonomous convergent extension morphogenesis in involuting cells |
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Symmetry in the amphibian blastula |
The blastula appears to have radial symmetry. It has an A-V axis. |
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Symmetry in the amphibian gastrua |
The gastrula exhibits bilateral symmetry. It has 3 axes: A-V A-P D-V |
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Who was Hans Spemann and why is he important? |
He was a German embryologist He explored the question: What promotes gastrulation? He worked with a variety of amphibians and performed a variety of transplant studies to examine the "pre-destiny" of tissues He won a nobel prize for his work in 1935 |
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Describe the Spemann's zygote dissection experiment. |
The gray crescent in an amphibian embryo can be observed at fertilization. He cut a zygote through the gray crescent, duplicating the first division, and from the two halves, two complete organisms formed. He then cut a zygote abnormally, one half had gray crescent and the other did not. The half with gray crescent formed a complete organism. The other half formed a "belly piece" The sorsal blastopore lip forms at the gray crescent. |
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What did Hans Spemann and Hilde Mangold do together? |
They performed xenotypic transplants using two different species of newt. They discovered the organizer (as it relates to the amphibian bauplan) They described primary induction. |
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Describe Spemann and Mangold's xenotypic newt transplant experiments. |
They took a portion of the dorsal blastopore lip from the donor newt and transferred it to the ventral region of a host newt. It caused two invaginations to occr in the blastopore Conjoined twins, attached ventrally, were produced |
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What is produced from the dorsal blastopore lip? |
The DBL induces the production of ventral structures. It produces the notochord (axial mesoderm), the lower part of the neural tube (notoplate) , and part of the somitic mesoderm. |
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Describe primary induction |
A process specific to vertebrates Tissue is induced: chordomesoderm (DBL in amphibians) the organizer (Spemann-Mangold organizer in ambhibians) Acts globally to: specify axes "establish" germ layers and germ layer regions induce the CNS |
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Who was Pieter Nieuwkoop and why is he important? |
He was a Dutch embryologist who specialized in amphibian embryonic anatomy He researched inductive interactions: neural induction mesendoderm induction germ cell induction |
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Fate of the amphibian blastula regions when isolated |
Animal cap cells- ectoderm Vegetalcells- vegetal mass
Ventral marginal zone- mesoderm- blood, epidermis, mesenchyme Dorsal marginal zone- mesoderm- muscle, neural tube, notochord |
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Recombination of animal cap cells and vegetal cells |
Mesodermal tissue, such as mesenchyme, muscle, and notochord, is induced. Vegetal cells are a source of inductive signal |
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Gimlich and Gerhart dorsal vegetal cell transplants |
UV-Irradiated recipient cells. UV destroys microtubules and the gray crescent can't form because there is no cortical rotation. The UV recipient will form only a belly piece. The UV recipient that got vegetal cells from a donor underwent complete development. Transplant of vegetal cells to another normal recipient induced a new gastrulation site and additional body axis formation, creating another head located next to the first |
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Where is the Nieuwkoop center and what is its purpose? |
It is located opposite the site of sperm entry on an embryo. Autonomous specification causes determinants to move to establish the Nieuwkoop center The Nieuwkoop center sends signals above itself to the marginal zone, which is induced to become the organizer |
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Which organisms are basal metazoans? |
porifera and cnidaria |
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Characteristics of porifera |
sponges parazoa- not "true" metazoans asymmetrical body plan no true germ layers limited number of cell morphotypes: no muscles or nerves Resemble a perforated bag Choanocyte, archeocyte (amebocyte) |
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poriferan development |
Holoblastic cleavage Variable cleavage patterns Form coeloblastulae and/or stereoblastulae Exhibit widely varied modes of gastrulation and resulting larvae |
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Cnidarian model organisms |
Hydra Sea anemone |
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Cnidarian bauplan |
radial symmetry diploblasts -ectoderm- epidermis- sensory cells, cnidoblasts, interstitial cells -endoderm- gastrodermis- muscle, neurons, gland cells - mesoglea between the germ layers- ECM, connective tissue |
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Cnidarian embryology |
Simplistic but varied Primarily anarchic: no observable patterns Blastulae: coeloblastulae, stereoblastulae Gastrulation forms: ingressions, delaminations, invagination, epiboly Form a planula larva |
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Fate of stem cells in cnidarians |
Multipotent stem cells create:
-nematocytes -nerve cells -gland cells -egg lineage stem cells -> eggs -sperm lineage stem cells -> sperm |
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Ecdysozoans model organisms |
C. elegans The nematode Drosophila melanogaster The fruit fly Arthropod/insect |
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Ecdysozoa characteristics |
bilaterans protostomes ecdysis- molting metamerism- body segmentation |
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C. elegans bauplan |
Pseudocoelomate: outer tube- hypodermis, muscle inner tube- digestive tract (including pharynx), reproductive tract, no mesoderm boundary hermaphrodite gonad sequential hermaphrodite: male then female: make sperm, sore it, make eggs, and self-fertalize (internally) Every adult is identical (959 somatic cells) and has identical development (invariant cell lineage) |
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C. elegans embryology |
Isolecithal egg, elongate along A-P axis Holoblastic cleavage; rotational cleavage pattern 24-cell blastula doesn't undergo true gastrulation- migration of cells is minimal complete lineage map known |
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C. elegans 4-cell stage |
AB -> ABp & ABa P1 -> EMS & P2 |
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What is the importance of P granules? |
They are the determinants of the P cells and their germ line descendants |
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C. elegans founder cells |
p-cells: germline C, D: mesoderm ABa: pharynx, hypodermis, neurons ABp: hypodermis, neurons MS: mesoderm, including pharynx E: endoderm |
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What is the nematode cuticle made of? |
collagens |
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Drosophila body characteristics |
head- fused segments used for feeding thorax- locomotory appendages abdomes- respiration and reproduction |
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Drosophila reproductive system |
Ovary composed of ovarioles Germerium- site of oogonium Vitellarium- site of egg maturation Internal fertilization Spermatheca- sperm storage organs |
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Formation of oocyte and nurse cells |
4 rounds of mitosis to produce 16 cells Cells have ring connections. Only 2 cells have 4 ring connections. One of these becomes the oocyte. The others become nurse cells. |
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What contributes to Drosophila oocyte maturation? |
Nurse cells- produce mRNA/ protein determinants Yolk- fat bodies are the site of yolk production Follicle cells- induce oocyte (produce vitelline envelope), produce chorion for protection, and produce embryonic polarity |
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Drosophila embryology |
centrolecithal egg (yolk central) superficial cleavage (karyokinesis, no cytokinesis) |
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Stages of Drosophila cleavage |
1. syncytial stage 2. syncytial blastoderm 3. pole cell formation 4. Cellularization via formation of furrow canals and acquisition of membrane vessicles |
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Drosophila gastrulation events |
Furrow formation: ventral furrow (internalization of mesoderm) cephalic furrow (separate head from body) Germ band extension convergent extension of mesoderm and ectoderm elongation of embryo formation of gut tube neuroectoderm ventral ingression segmentation Germ band retraction shorten A-P axis, lengthen D-V axis |
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Long germ band insect development |
cellular blastoderm produces head, thorax abdomen |
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Short germ band insect development |
cellular blastoderm produces the head only the growth zone produces the rest of the organism |
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Intermediate germ band insect development |
cellular blastoderm produces the head and thorax the growth zone produces the rest of the organism |
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Lophotrochozoan characteristics |
bilaterians protostomes ciliated have lophophore, a ciliated feeding structure |
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Eutrochozoan characteristics |
used ciliated structures for locomotion trochophore larva spiral cleavage |
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Examples of Eutrochozoans |
Annelids - specialization at anterior and posterior ends anterior = head = acron posterior = pygidium Molluscs- veliger- have velum, shell, foot, visceral mass, and shell gland Nemerteans Platyhelminthes- flatworms |
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Trochophore larva |
have apical tuft and apical organ to sense orientation have trochal band (ciliary ring) for locomotion |
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What is clockwise cleavage called? |
Dexiotropic Dextral |
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What is counter-clockwise cleavage called? |
Laeotropic Sinistral |
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How are spirally cleaving cells categorized? |
quadrants: letters: A, B, C, D quartets: layers all micromeres derived from one cleavage of the macromeres numbers |
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Eutrochozoan generalized fate map |
micromeres: ectoderm of larva macromeres (after generation of 3rd quartet): larval endoderm 3a, 3b, 3c: (ecto)mesoderm 2d: sometoblast- adult ectoderm 4d: mesentoblast- adult mesoderm and andoderm |
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Annelids growth zone |
The larval form becomes reorganized to form the head of the adult The trunk is produced from a growth zone |
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4 stage Eutrochozoan cell isolations |
A, B, C- produce a subset of cells expected D- regulates to produce larva- organizer induced by micromeres- touching the most always gets polar lobe (extra cytoplasm bubble) |
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Types of chordates |
Urochordates Cephalochordates Vertebrates |
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Types of vertebrates |
Amniotes- reptiles, birds, mammals- have amnion (fluid-filled tissue that supports development "outside" of water) Anamniotes- fish, amphibians- lack amnion |
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Vertebrate characteristics |
Cephalization Appendages Endoskeleton of bone and cartilage Neural crest |
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Hemi- Chordates |
Half-chordates Display some chordate features |
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Example of urochordate & characteristics |
Tunicates (Ascidians) ((Holoblastic & bilateral cleavage)) ((Bilaterally symmetrical coeloblastula)) ((Six tissues after gastrulation)) |
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What is the myoplasm
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Tail muscle Develops from yellow crescent |
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Urochordate gastrulation events |
Invagination of endoderm Involution of mesoderm Epiboly of ectoderm |
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Urocjordate embryology |
Autonomous specification of most rissues Conditional signaling from A4.1 |
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Cephalochordate example and characteristics |
Amphioxus Radial cleavage 256-cell coeloblastula Similar fate map to urochordates and amphibians |
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Cephalochordate gastrulation events |
Invagination of endoderm |
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Isolation of cephalochordate cells at 4-cell stage |
All produce complete larvae Also, animal tier + vegital tier = complete larvae |