Chapter 47 Animal Development

From eggs to organisms

Figure 47.1 A “homunculus” inside the head of a human sperm

Preformation: a series of successively smaller embryos within embryos

Epigenesis: the form of animal emerges gradually from a formless eggs( Aristotle)

Fertilization activate the egg and brings together the nuclei of sperm and eggs

1. The Acrosomal reaction

release of enzyme from acrosomal vesicle

elongation of acrosomal process and penetration

through jelly coat

binding of acrosomal process to specific

receptors on eggs

fusion of sperm and egg plasma causes influx of

sodium and membrane depolarization

fast block to polyspermy

2. The Cortical reaction

release of Ca+2 from the site of sperm entry

2nd messenger ( IP and DAG) induced by Ca+2

release opens Ca+2 channel on egg's’s ER

cortical granule release content into periventilline

layer

formation of fertilization envelope) slow block to

poly spermy

Figure 47.2 The acrosomal and cortical reactions during sea urchin fertilization

Figure 47.3 A wave of Ca2+ release during the cortical reaction

3. Activation of eggs

DAG activate H+ channel , causes pH change

and induce metabolic rate

fusion of sperm and egg nucleus

DNA synthesis begin

cell division begins in 90 minutes

Figure 47.4 Timeline for the fertilization of sea urchin eggs

Fertilization of mammals

1. Migration of sperm through follicle cells

2. Binding induces acrosomal reaction

3. Binding of sperm cells to ZP3 receptor in coat of

zona pellucida

4. Nucleus of both eggs and sperm did not fuse until the 1st division of the zygote

Figure 47.5 Fertilization in mammals

Cleavage partitions the zygote into many smaller cells

Three stages after fertilization

1. Cell division 細胞分裂期

cell undergo S and M phase of cell cycle but skip

G1 and G2 phase

partition cytoplasm of zygote into many smaller

cells called blastomere ( distribution of different

cytoplasmic content in the different regions)

polarity defined by substances that are

heterogeneously distributed in the cytoplasm of

the eggs

Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo

45-90 min after fertilization

Figure 47.7 The establishment of the body axes and the first cleavage plane in an amphibian

(More concentrate yolk)

灰月區

Figure 47.8x Cleavage in a frog embryo

Animal pole

Vegetal pole

2. Gastrulation 原腸期

rearrangement of cells of blastula

transformation of blastula into three layer embryonic germ layer

ectoderm: nervous system and outer layer of skin

endoderm: digestive tract and associated organs

mesoderm: dermis, kidney, hearts, muscles…

Figure 47.9 Sea urchin gastrulation (Layer 1)

Figure 47.9 Sea urchin gastrulation (Layer 2)

Figure 47.9 Sea urchin gastrulation (Layer 3)

Figure 47.10 Gastrulation in a frog embryo

Table 47.1 Derivatives of the Three Embryonic Germ Layers in Vertebrates

外胚層

內胚層

中胚層

3. Organogenesis 器官形成

folds, splits and dense clustering( condensation)

of cells

notochord ( dorsal mesoderm)neuroplate(

dorsal ectoderm)

somite ( mesoderm) backbone of animals axial

skeleton

morphogenesis and differentiation continue to

refine organs as they formed

Figure 47.11 Organogenesis in a frog embryo

Amniote embryos develop in a fluid filled sac with shell or uterus

Amniotes: within the shells or uterus, embryos

surrounded by fluid within a sac formed by

membrane called amnion

Avian development

meroblastic cleavage : cell division occurs only in

a small yolk-free cytoplasm atop of the large mass

of yolk

The tissue layer out side the embryo develop into

four extra embryonic membrane( yolk sac, amnion,

chorion, and allantois)

Figure 47.12 Cleavage, gastrulation, and early organogenesis in a chick embryo

Figure 47.13 Organogenesis in a chick embryo

Figure 47.14 The development of extra embryonic membranes in a chick

(Waste storage)

( filled with amnionic fluid for protection)

Figure 47.15 Early development of a human embryo and its extraembryonic membranes

7 days, 100 cells

implantation

Development of extraembryonic membrane

Inward movement of epiblast starts the gatrulation

The cellular and molecular basis of morphogenesis and differentiation in Animals

Morphogenesis: cell movement , shape and position

change of developing cells

invagination and evagination

Figure 47.16 Change in cellular shape during morphogenesis

Figure 47.17 Convergent extension of a sheet of cells

Convergent extension:

cells of tissue layer rearrange to become narrower

and longer

Possible guide by ECM( Ecm act as a track to guide

the movement of the cells)

Figure 47.18 The extracellular matrix and cell migration

Figure 47.19 The role of a cadherin in frog blastula formation

CAM: cell adhesion molecule

cadhesrin

Experimental: inject with antisense cadhedrin

control

The developmental fate of cells depends on the cytoplasmic determinants and cell-cell induction

1. The heterogeneous distribution of cytoplasmic

determinants in the unfertilized eggs lead to

regional differentiation in the early embryo

2. Induction, interaction among the embryo cells

themselves induces gene experssion

Figure 47.20 Fate maps for two chordates

Figure 47.21 Experimental demonstration of the importance of cytoplasmic determinants in amphibians

Figure 47.22 The “organizer” of Spemann and Mangold

Primary organizer of embryo

BMP-4( bone morphogenic proteins)

Locate at ventral side of gastrula

Organizer produce proteins to inhibit the BMP-4

activity

Figure 47.23 Organizer regions in vertebrate limb development

AER

AER( Apical Ectodermal Ridge)

required for proximal-distal axis and patterning of

this axis

EGF: epidermal growth factor is responsible for the

growth signal

ZPA (Zone of Polarizing Area)

Responsible for pattern formation along anterior-

posterior axis

secret sonic hedgehog, which is important for the

growth of limb bud growth

Figure 47.24 The experimental manipulation of positional information

Figure 47.6x Sea urchin development, from single cell to larva

Figure 47.8d Cross section of a frog blastula

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