Download Developmental Biology 8/e

Early Mammalian Development
Axis determination
Neural Development
세포생물학 2 (임현정)
June 5, 2009
Axes and planes of section used for describing embryos
Axis
A-P
D-V
L-R
11.27 Development of a human embryo from fertilization to implantation
Early mammalian embryonic development
Development of a human embryo from fertilization. Compaction of the human embryo occurs on day 4,
when it is at the 10-cell stage. The embryo hatches from the zona upon reaching the uterus. The zona
prevents the embryo from prematurely adhering to the oviduct.
Preimplantation development in mice
(Gestation length: 20 days)
Day 1
Day 2
Day 3
(zona 생략)
Day 4
11.29 Cleavage of a single mouse embryo in vitro
Cleavage of a single mouse embryo in vitro.
11.31 Hatching from the zona and implantation of the mammalian blastocyst in the uterus
Hatching from the zona pellucida and implantation of the mammalian blastocyst in the uterus. (A) Mouse
blastocyst hatching from the zona. (B) Mouse blastocysts entering the uterus. (C) Initial implantation of the
blastocyst in a rhesus monkey.
11.33 Tissue formation in the human embryo between days 7 and 11 (Part 1)
Tissue formation in the human embryo
between days 7 and 11.
(A,B) Human blastocyst immediately prior to
gastrulation. The inner cell mass delaminates
hypoblast cells that line the blastoceol,
forming the extraembryonic endoderm of the
primitive yolk sac and a two-layered (epiblast
and hypoblast) blastodisc. The trophoblast
divides into the cytotrophoblast, which will
form the villi, and the syncytiotrophoblast,
which will ingress into the uterine tissue.
11.33 Tissue formation in the human embryo between days 7 and 11 (Part 3)
Tissue formation in the human embryo
between days 7 and 11.
(C) Meanwhile, the epiblast splits into the
amniotic ectoderm (which encircles the
amniotic cavity-blue) and the embryonic
epiblast (purple”embryo proper”). The adult
mammal forms from the cells of the
embryonic epiblast.
(D) The extraembryonic endoderm forms the
yolk sac. The actual size of the embryo at this
stage is about that of the period at the end
of this sentence.
Amnion structure and cell movements during human
gastrulation. (A,B) Human embryo and uterine
connections at day 15 of gestation. (A) Sagittal
section through the midline. (B) View looking down
on the dorsal surface of the embryo. (C) The
movements of the epiblast cells through the
primitive streak and Hensen’s node and underneath
the epiblast are superimposed on the dorsal surface
view. At days 14 and 15, the ingressing epiblasts are
thought to replace the hypoblast cells, while at day
16, they fan out to form the mesodermal layer.
11.32 Schematic diagram showing the derivation of tissues in human and rhesus monkey
embryos
Schematic diagram showing the derivation of tissues in humans and rhesus monkey embryos.
The dashed line indicates a possible dual origin of the extraembryonic mesoderm.
11.30 Maintaining lineages in the mouse blastocyst
Maintaining lineages in the mouse blastocyst. Proposed functions of the Nanog, Oct4, and Stat3 proteins in
retaining the uncommitted pluripotent fate of embryonic cells. Oct4 stimulated the morula cells retaining its
expression to become “Inner Cell Mass (ICM)” and not trophoblast. Nanog works at the next differentiation
event, preventing the ICM cells to becoming hypoblast, and promoting their becoming the pluripotent
embryonic epiblast. Stat3 is probably involved in the self-renewal of these pluripotent cells. Meanwhile, Cdx2
in the trophoblast prevents Oct4 and Nanog expression, thereby stabilizing the trophoblast lineage.
11.35 Human embryo and placenta after 50 days of gestation
Human embryo and placenta after 50 days of
gestation. The embryo lies within the amnion, and
its blood vessels can be seen extending into the
chorionic villi.
Amnion (양막)
Chorion (융모막)
Yolk sac (난황막)
11.36 Relationship of the chorionic villi to the maternal blood supply in the uterus
Relationship of the chorionic villi to the maternal blood supply in the uterus.
11.37 The timing of human monozygotic twinning with relation to extraembryonic membranes
Diagram showing the timing of human monozygotic twinning with relation to extraembryonic membranes.
(A) Splitting occurs before the formation of the trophoblast, so each twin has its own chorion and amnion.
(B) Splitting occurs after trophoblast formation but before amnion formation, resulting in twins having
individual amnionic sacs but sharing one chorion. (C) Splitting after amnion formation leads to twins in one
amnionic sac and a single chorion.
Axis determination: Anterior-posterior patterning in the mouse embryo
Key points to remember in A-P Patterning
1. Signaling centers
2. Gastrulation
3. Morphogen gradient
4. Hox genes
Mesodermal induction by the
vegetal endoderm in Xenopus
Functions of the organizer:
1.The ability to self-differentiate dorsal
mesoderm (chordamesoderm)
2.The ability to dorsalize the surrounding
mesoderm into paraxial mesoderm (somites,
etc.)
3.The ability to dorsalize the ectoderm,
inducing the formation of the neural tube
4.The ability to initiate the movements of
gastrulation
Signaling centers
1.
다른 종에서는 Organizer (양서류) 또는 Hensen’s node (닭) 으로 불리운다.
2.
포유류에는 2개가 있다: the node, the anterior visceral endoderm (AVE).
3.
Node는 전체 body patterning을 조절하며 node와 AVE가 협력하여 배아의 머리쪽 구조를 형성한다.
4.
Neural tube를 유도하는 notochord는 node의 ciliated cell들이 등쪽으로 들어가면서 형성된다.
5.
Chordamesoderm인 notochord는 ectoderm 의 일부를 neural tube로 유도한다.
11.39 Axis and notochord formation in the mouse (Part 1)
Day 7
Axis and notochord formation in the mouse. (A) In the
7-day mouse embryo, the dorsal surface of the epiblast
(embryonic ectoderm) is in contact with the amnionic
cavity. The ventral surface of the epiblast contacts the
newly formed mesoderm. In this cuplike arrangement,
the endoderm covers the surface of the embryo. The
node is at the bottom of the cup. The two signaling
centers, the node and the anterior visceral endoderm
(AVE), are located on opposite sides of the cup.
Eventually, the notochord will link them. The caudal side
of the embryo is marked by the presence of the allantois.
AVE: Nodal protein의 antagonist인
Lefty1과 Cerberus, Wnt inhibitor인
Dickkopf를 발현한다. 즉 posterior
region 형성에 필요한 유전자들을
저해함으로써 anterior 구조형성에
기여한다.
11.39 Axis and notochord formation in the mouse (Part 2)
Day 8
Axis and notochord formation in the mouse. (B) By embryonic day 8, the AVE lines the foregut, and the
prechordal mesoderm is now in contact with the forebrain ectoderm. The node is now father caudal, due largely
due to the rapid growth of the anterior portion of the embryo.
11.39 Axis and notochord formation in the mouse (Part 3)
Ventral surface of a 7.5-day mouse embryo.
The presumptive notochord cells extend
from the node into the endoderm of the
primitive gut, converging medially to begin
formation of the notochord.
Node
Embryonic turning. In mice, from about embryonic day 7.5 to 9, the embryo becomes rotated around its long axis
leading to ventral closure of the gut.
Morphogen gradient
A stable concentration gradient: cannot be produced simply by
releasing a pulse of the morphogen.
조건: “source” and “sink”  gradient 형성
중요개념:
Threshold responses
Polarity
“Mirror symmetry”
그림 설명: Properties of morphogen gradients.
(a)Normal development of an animal with a head and
three segments.
(b)Graft of the posterior source to the anterior causes
formation of a U-shaped gradient and produces a
double-posterior animal.
(c)Insertion of an impermeable barrier causes formation of
a large gap in the pattern. The binary codes indicate the
activity in each body region of the genes, 3,2, and 1,
respectively (1=on, 0=off).
Anterior-posterior patterning in the mouse embryo
(A) Concentration gradients of BMPs, Wnts, and FGFs in the late gastrula mouse embryo (depicted as a
flattened disc). The primitive streak and other posterior tissues are the sources of Wnt and BMP proteins,
whereas the organizer and its derivatives produce antagonists. (C) Retinoic acid, Wnt3a, and Fgf8 each
contribute to posterior patterning, but they are integrated by the Cdx family of proteins that regulate the activity
of the Hox genes.
11.40 Expression of BMP antagonists in the mammalian node
Expression of BMP antagonists in the mammalian node.
Homeotic genes
(A) A head of a wild-type fruit fly.
(B) Head of a fly containing the Antennapedia
mutation that converts antenna into legs.
3`
Evolutionary conservation of homeotic gene organization in fruit flies and mice.
5`
* Homeotic genes: mutations of those lead to homeotic transformations of specific segments
along the AP body axis
1.
2.
3.
4.
5.
6.
Homeobox (183-bp)
Transcription factors
(61-aa homeodomain)
Temporal colinearity
Spatial colinearity
Chromosomal duplication
Autoregulation or cross-regulation
Paralogous group
paralogous group
* Hox gene expression domains in the developing vertebral column
vertebrae
occipital
bone
Experimental analysis of the Hox code
1. Gene targeting
2. Retinoic acid teratogenesis
3. Comparative anatomy
11.43 Axial skeletons of mice in gene knockout experiments
Gene targeting
Lumbar  thoracic
Sacral  lumbar
11.44 The effect of retinoic acid on mouse embryos (Part 1)
Retinoic acid teratogenesis
11.44 The effect of retinoic acid on mouse embryos (Part 2)
11.45 Schematic representation of the chick and mouse vertebral pattern along the anteriorComparative
anatomy
posterior
axis (Part
1)
Axis determination: Left-right patterning in the mouse embryo
Key points to remember
1. Ciliary cells in the node
2. NVPs
3. Mutations
11.47 Left-right asymmetry in the developing human
Left-right asymmetry in the developing human.
(A) Abdominal cross sections show that the originally symmetrical organ rudiments acquire asymmetric positions
by week 11. The liver moves to the right and the spleen moves to the left. (B) Not only does the heart move to the
left side of the body, but the originally symmetrical veins of the heart regress differentially to form the superior
and inferior venae cavae, which connect only to the right side of the heart. (C) The right lung branches into three
lobes, while the left lung (near the heart) forms only two lobes. In human males, the scrotum also asymmetrically.
Normal
Polysplenia syndrome
Asplenia syndrome
(no spleen)
Complete mirror-image reversal
The left-right axis
1. The mammalian body is not symmetrical.
2. situs inversus viscerum (iv): randomizes the left-right axis for each asymmetrical organ
independently (Hummel & Chapman, 1959; Layton, 1976)
3. Lack of coordination among visceral organs can cause serious problems, even death.
4. inversion of embryonic turning (inv): Mice homozygous for an insertional mutation at this
locus had all their asymmetrical organs on the wrong side of the body. Since all the organs
were reversed, this asymmetry did not have dire consequences for the mice.
Ciliary cells in of the node
1. The cilia cause fluid in the node to flow from right to left.
2. KIP3B knockout mice: Nodal cilia did not move, and the situs (lateral position) of each
asymmetric organ was randomized.
11.48 Situs formation in mammals (Part 1)
Situs formation in mammals.
(A)Ciliated cells of the mammalian node.
(B)Schematic drawing showing the FGF-induced
secretion of nodal vesicular parcels from the cells of
the node, the movement of the NVPs to the left side,
motivated by the ciliary currents, and the rise in
Ca2+ concentration on the left side of the node.
NVP: small membrane-bound vesicles of 1 um.
They contain Sonic hedgehog protein and
retinoic acid, etc.
11.48 Situs formation in mammals (Part 3)
Situs formation in mammals.
(C) Calcium ions (red, green) concentrated on the
left side of the node in mice.
12.1 Major derivatives of the ectoderm germ layer
The emergence of ectoderm: Central Nervous System (CNS)
Major derivatives of the ectoderm germ layer.
Head fold stage
Ectoderm
1.Neural ectoderm
2.Neural crest cells
3.Epidermal ectoderm
Neural ectoderm: neural tube라는 rudiment를
만들어서 분화되는데, 이 과정을 neurulation이라
한다.
Neurulation in a chick embryo (dorsal view).
The cephalic (head) region has undergone
neurulation, while the caudal (tail) regions
are still undergoing gastrulation.
12.3 Primary neurulation: neural tube formation in the chick embryo (Part 1)
Primary neurulation: neural tube formation in the chick embryo.
(A,1) Cells of the neural plate can be distinguished as elongated cells in the dorsal region of the ectoderm. Folding begins
as the medial neural hinge point (MHP) cells anchor to the notochord and change their shape, while the presumptive
epidermal cells move toward the dorsal midline.
(B,2) The neural folds are elevated as the presumptive epidermis continues to move toward the dorsal midline.
12.3 Primary neurulation: neural tube formation in the chick embryo (Part 2)
Primary neurulation: neural tube formation in the chick embryo (II).
(C,3) Convergence of the neural folds occurs as the dorsolateral hinge point (DLHP) cells become wedge-shaped and the
epidermal cells push toward the center.
(D,4) The neural folds are brought into contact with one another, and the neural crest cells link the neural tube with the
epidermis. The neural crest cells then disperse, leaving the neural tube separate from the epidermis.
12.4 Three views of neurulation in an amphibian embryo (Part 1)
Three views of neurulation in an amphibian embryo, showing early (left), middle (center), and late (right)
neurulae in each case.
(A) Looking down on the dorsal surface of the whole embryo
12.4 Three views of neurulation in an amphibian embryo (Part 3)
Three views of neurulation in an amphibian embryo, showing early (left), middle (center), and late (right)
neurulae in each case.
(B) Sagittal section through the medial plane of the embryo.
(C) Transverse section through the center of the embryo.
12.5 Neurulation in the human embryo (Part 1)
Neurulation in the human embryo.
(A)Dorsal view of a 22-day (8-somite) human embryo initiating neurulation. Both anterior and posterior neuropores are
open to the amniotic fluid.
(B)10-somite human embryo showing the three major sites of neural tube closure (arrows).
(C)Dorsal view of a neurulating human embryo with only its neuropores open.
(D)A stillborn infant with ancephaly.
12.6 Expression of N- and E-cadherin adhesion proteins during neurulation in Xenopus
Expression of N- and E-cadherin adhesion proteins during neurulation in Xenopus.
(A)Normal development. In the neural plate stage, N-cadherin is seen in the neural plate, while E-cadherin is seen on the
presumptive epidermis. Eventually, the N-cadherin-bearing neural cells separate from the E-cadherin-containing
epidermal cells. (Neural crest cells express neither of them and they disperse.)
(B)No separation of the neural tube occurs when one side of the frog embryo is injected with N-cadherin mRNA, so that
N-cadherin is expressed in the epidermal cells as well as in the presumptive neural tube.
12.7 Folate-binding protein in the neural folds as neural tube closure occurs
Folate-binding protein in the neural folds as neural tube closure occurs.
(A)10-somite mouse embryo stained for folate-binding protein mRNA.
(B,C) Sections through embryo (A) at the two arrows, showing the folate-binding protein (dark blue) at the points of
neural tube closure.
Secondary neurulation in the caudal region of a 25-somite chick embryo.
(A)Mesenchymal cells condense to form the medullary cord at the most caudal end of the chick tailbud.
(B)The medullary cord at a slightly more anterior position in the tailbud.
(C)The neural tube is cavitating and the notochord forming; note the presence of separate lumens.
(D)The lumens coalesce to form the central canal of the neural tube.
Differentiation of the Neural Tube
Early human brain development. The three primary brain vesicles are subdivided as development continues. At the right
is a list of the adult derivatives formed by the walls and cavities of the brain.
12.10 Rhombomeres of the chick hindbrain
Rhombomeres of the chick hindbrain.
12.12 Occlusion of the neural tube allows expansion of the future brain region
Occlusion of the neural tube allows expansion of the future brain region.
(A)Dye injected into the anterior portion of a 3-day chick neural tube fills the brain region, but does not pass into the
spinal region.
(B,C) Sections of the chick neural tube at the base of the brain (B, before occlusion, C, during occlusion).
(D) Reopening of the occlusion after initial brain enlargement allows dye to pass from the brain region into the spinal
cord region.
12.13 Dorsal-ventral specification of the neural tube (Part 1)
Dorsal-ventral specification of the neural tube.
Two signaling centers:
ectoderm  roof plate (BMP)
notochord  floor plate (Shh)
12.14 Cascade of inductions initiated by the notochord in the ventral neural tube (Part 2)
(B) Two cell types in the newly formed neural tube. Those closest to the notochord become the floor plate
neurons; motor neurons emerge on the ventrolateral sides.
(C) If a second notochord, floor plate, or any other Sonic Hedgehog-secreting cell is placed adjacent to the
neural tube, it induces a second set of floor plate neurons, as well as two other sets of motor neurons.
Schematic representation of neural crest formation in a chick embryo,
shown in cross section. Neural crest cells form at the junction between the
Wnt6-expressing epidermal ectoderm and the BMPs produced by the
presumptive neural ectoderm.
13.2 Regions of the chick neural crest
Regions of the chick neural crest. The cranial neural crest migrates into the pharyngeal arches and the face to form
the bones and cartilage of the face and neck. It also produces cranial nerves. The vagal neural crest (near somites 1-7)
and the sacral neural crest (posterior to somite 28) form the parasympathetic nerves of the gut. The cardiac neural
crest cells arise near somites 1-3; they are critical in making the division between the aorta and the pulmonary artery.
Neural crest cells of the trunk (about somite 6 through the tail) make sympathetic neurons and pigment cells
(melanocytes), and a subset of these (at the level of somites 18-24) form the medulla portion of the adrenal gland.
Pluripotency of trunk neural crest cells. (A) A single neural crest cell is injected with highly fluorescent dextran
shortly before migration of the neural crest cells is initiated. The progeny of this cell each receive some of these
fluorescent molecules. Two days later, neural crest-derived tissues contain dextran-labeled cells that are descended
from the injected precursor. The figure summarizes data from two different experiments.
13.7 Pluripotency of trunk neural crest cells (Part 2)
Pluripotency of trunk neural crest cells. (B) Model for neural crest lineage segregation and the heterogeneity of
neural crest cells. The committed precursors of neurons (N), glias (G), melanocytes (M), and so forth would be
derived from intermediate progenitors, some of which could act as stem cells. The multipotent neural crest stem cell
(top) is hypothetical and need not exist.