Developmental Biology
An Understanding of Everything
Stages & Events of Chordate Embryogenesis
Developmental Process
Embryonic Stage
Zygote
Morula
Blastula
Gastrula
Neurulation
Neurula
Pharyngula
Fetus
Gametogenesis
• Process of producing gametes
 Spermatogenesis
 Oogenesis
• Meiotic cell division
• Packaging of material into oocytes
• Removal of cytoplasm from sperm
Accumulation of Vitellogenin during Oogenesis in Xenopus
Localization of Developmental Regulatory Factors
• Dsh, Xcat-2, Xlsirt, Vg-1 mRNAs localized to vegetal
pole of vertebrate eggs
Xlsirt mRNA
Bicoid Gradient in Drosophila Egg & Embryo
Fertilization - Sperm and Egg Fusion
Fertilization Induces a Rearrangement of Cytoplasmic, Localized Factors
• Initial localization of material in eggs is radially symmetrical
• Fertilization creates a point of asymmetry and causes
rotational reorganization of cytoskeleton to generate bilateral
symmetry
Gray crescent
Reorganization of Cytoplasmic Maternal Factors Set Up Signaling Cascades
Figure 20.12 Molecular Mechanisms of the Primary Embryonic Organizer
Cleavage Distributes Maternal Components to Blastomeres
Figure 19.7 Asymmetry in the Early Embryo (Part 1)
Figure 19.7 Asymmetry in the Early Embryo (Part 2)
Autonomous Development of Separated Tunicate Blastomeres
Figure 19.8 The Principle of Cytoplasmic Segregation
Figure 20.10 Hans Spemann’s Early Experiments
Figure 20.11 The Dorsal Lip Induces Embryonic Organization
Fate Map of a Frog Blastula
Figure 20.9 Gastrulation in the Frog Embryo (Part 1)
Figure 20.9 Gastrulation in the Frog Embryo (Part 2)
Figure 20.9 Gastrulation in the Frog Embryo (Part 3)
Figure 20.15 Neurulation in the Frog Embryo (Part 1)
Figure 20.15 Neurulation in the Frog Embryo (Part 2)
Figure 20.13 Gastrulation in Amniotes (Part 1)
Figure 20.13 Gastrulation in Amniotes (Part 2)
Figure 20.16 The Development of Body Segmentation
Mouse embryo
Drosophila Homeotic and Vertebrate Hox Genes Control A-P
Patterning
Hox Genes Pattern A-P Axis
Concepts in Developmental Biology
• Polarity
 Established by localization of maternal gene products
 Established by inductive signaling events
• Morphogenesis
 Cellular movements and embryonic structure formation
 Regulated by cell-signaling & cell adhesion mechanisms
• Differentiation
 Specialization of cells to a particular fate
• Growth
 Increase in cell number
 Increase in cell size
Cell Specification
• Differentiation
 The process and the processes associated with a cell
becoming specialized
 Occurs in multiple steps
Cell Specification
• Autonomous
 All differentiation information is
contained within the cell
• Conditional
 Differentiation information supplied
through interactions with other cells
Cell Specification - Steps
• Commitment
 Specification
 Determination
• Terminal differentiation
Cell Specification - Commitment
• Specification
 A cell is said to be specified when:
 Cells differentiate autonomously when removed from normal
environment (embryo) and placed in a neutral environment
(culture medium)
 Placing cells into a non-neutral environment (a different place in
the embryo) causes the cells to follow the fate of other cells the
new location rather than their original fate
Cell Specification - Committment
• Determination
 A cell is said to be determined when:
 Cells differentiate autonomously even when placed in
a non-neutral environment
 When moved to a different location within the embryo,
the transplanted cells differentiate according to their
original fate
Cell Specification - Terminal Differentiation
• When a cell can no longer change or be changed into anything other
than the cell type it is
• Can be associated with permanent changes in DNA
 DNA Methylation is a prominent factor
 B-cells (plasma cells) rearrange the immunoglobulin (Ig) genes
so that they can now only form a single type of Ig
Spemann’s Specification Experiments
Inductive signals trigger
conditional specification,
determination and
differentiation
Presumptive neural plate ectoderm in
the early gastrula was uncommitted.
Later gastrula neuroectoderm was
committed to a neural fate.
Dorsal Lip Transplantation
Reversal of Terminal Differentiation
• Embryonic Stem cells
 Totipotent or pluripotent cells
• Dedifferentiated stem cells
 Pluripotent
 Derived from previously differentiated cells
• Cloning proves nuclear equivalence
Figure 19.3 Cloning a Plant (Part 1)
Cloning by Nuclear Transplantation
• Nuclear transplant experiments have shown that
somatic cells contain the entire genome.
• Nucleus of an unfertilized egg is replaced with the
nucleus of a somatic cell
• These experiments led to two important
conclusions:
 No information is lost in the early stages of
embryonic development (a principle known as
genomic equivalence).
 The cytoplasmic environment around a nucleus
can modify its fate.
The First Cloning Experiment – Nuclear Transplantation in Xenopus laevis
Cloning of the frog Xenopus laevis by nuclear transplantation of
albino gut cell nuclei into enucleated, wt oocytes. All progeny
are albino & female
tadpole
oocyte
nucleus
First Mammalian Clone
Dolly & Bonnie
Figure 19.10 Induction during Vulval Development in C. elegans (Part 1)
Figure 19.10 Induction during Vulval Development in C. elegans (Part 2)
A Gene Cascade Controls Pattern Formation in the Drosophila Embryo
Maternal effect genes
Gap genes
Pair rule genes
Segment polarity genes
Homeotic genes
Bicoid and Nanos Protein Gradients Provide Positional Information (Part 1)
Figure 19.14 Bicoid and Nanos Protein Gradients Provide Positional
Information (Part 2)
Figure 19.16 A Homeotic Mutation in Drosophila
Antennapedia
Figure 19.12 Organ Identity Genes in Arabidopsis Flowers (Part 1)
Figure 19.12 Organ Identity Genes in Arabidopsis Flowers (Part 2)
Figure 19.13 A Nonflowering Mutant
Northern Analysis: Gel
Electrophoresis
Formaldehyde gels
Methyl-mercury-OH gels
Northern Analysis: Probing
Spatial expression information
RNA Localization
Developmental Stages
temporal expression information