Experimental developmental biology explores how organisms develop through controlled experiments, focusing on cellular differentiation and morphogenesis using model organisms due to their practicality and genetic homology to humans. Model organisms like Drosophila, C. elegans, zebrafish, and mice are pivotal in studying developmental processes and genetic phenomena, yielding vital discoveries in fields like neurobiology and gene regulation. This research is essential for advancing our understanding of human biology and disease through insights gained from the simpler systems of these model organisms.

1. EXPERIMENTAL
DEVELOPMENTAL BIOLOGY
(MODEL ORGANISMS)
Presented by Deepakshi Gayen
Reg No: 23LBMS26
MSc Biochemistry

2. Experimental Developmental
Biology:
Experimental developmental
biology involves controlled
experiments to investigate the
processes by which organisms
develop.
Research goals to understand:
 Cellular differentiation (how
cells become specialized).
 Morphogenesis (how tissues and
organs form).
 Ethics and Practicality: Easier
than working directly with
humans.
 Genetic Homology: Many
organisms share genes with
humans.
Criteria for Selecting Model
Organisms:
 Practical Features: Short
generation times, small size, and
high reproductive rate.
 Genetic Tractability: Genetic
tools (e.g., CRISPR/Cas9,
organs form).
 Organogenesis (formation of
functional organs).
Model organisms:
Model organisms are non-human
species that are studied to
understand biological processes
and how they relate to other
organisms.
Importance of Model Organisms:
 Reproducibility: Same species
can be used worldwide.
 Genetic Tractability: Genetic
tools (e.g., CRISPR/Cas9,
knockouts).
 Ease of Observation: Ability to
visualize development (e.g.,
transparent embryos).
 Conservation of Pathways:
Similar developmental pathways
(e.g., Hox genes, signaling
cascades) between model
organisms and humans.

3. Why Drosophila?
 One of the first genetically tractable
organisms used in developmental
research (T.H. Morgan, early 1900s).
 Short life cycle (10 days from egg to
adult).
 Four pairs of chromosomes
 14000 Genes, sequenced genome
and 2/3 of human disease genes have
Discoveries & Future Aspects:
 Discovery of homeotic (Hox) genes
Control the body plan of an organism.
 Study of pattern formation:
Establishment of anterior-posterior and
dorsal-ventral axes.
 Discovery of maternal effect genes
like bicoid: Control early patterning
of embryos.
Drosophila melanogaster (Fruit Fly)
and 2/3 of human disease genes have
fly homologues.
 Simple care requirements, cheap, and
robust genetic tools.
of embryos.
 In situ hybridization of whole
embryo can reveal patterns of gene
expression during development
 Polytene chromosome present in
salivary gland can be used to determine
binding site of labeled proteins.
Chromosomal rearrangments and
deletions can be visualized.

4. Nobel Prize Contributions:
1995: Edward Lewis, Christiane Nüsslein-Volhard, and Eric Wieschaus for
discovering genes that control embryonic development
Conservation of patterning between flies and mammals
anterior posterior
HoxA
(Hox 1)
parasegments
rhombomores
(Hox 1)
HoxB
(Hox 2)
E
E HoxC - - - - - - - 1
(Hox 3)
HoxD
(Hox 4)
rhombomores
1 2 3 4 5 6 7 8
VERTEBRATE

5. Why C. elegans?
 Simple body plan, transparent body,
and invariant cell lineage.
 Worms are usually kept on petri plates
and fed E.coli.
 959 somatic cell, all visible under
microscope. 131 cells undergo
programmed cell death.
 Genome contains 19000 fully
sequenced genes
Discoveries & Future Aspects:
 Apoptosis: Mechanisms of programmed
cell death elucidated.
 RNA interference (RNAi): Discovery
of gene silencing mechanisms by
Andrew Fire and Craig Mello (Nobel
Prize, 2006).
 Gene function studies have become
relatively simple with the recent
discovery of RNAi.
Caenorhabditis elegans (Nematode)
sequenced genes
 70% of human genes have worm
homologues.
 Only 302 neurons, making it ideal for
neurodevelopmental studies.
discovery of RNAi.
 Full connectome (complete map of
neural connections) mapped.
Key Genetic Techniques:
Gene knockdowns using RNAi,
CRISPR/Cas9 for gene editing.
Applications:
Aging studies, neurobiology, innate
immunity.

6. Why Zebrafish?
 Vertebrate model with clear
homologs to human genes.
 Transparent embryos allow real-
time observation of organogenesis.
 Rapid development: Major organs
form within 24-48 hours post-
fertilization.
Discoveries & Future Aspects:
 Role of Notch signaling in
segmentation.
 Insights into heart development and
regeneration (zebrafish can
regenerate heart tissue).
 Genetic basis of organ development:
Kidney, liver, and pancreas.
Danio rerio (Zebrafish)
Applications:
Cardiovascular biology, cancer
biology, drug screening.

7. Why Xenopus?
 Large, easily manipulated embryos
ideal for studying early embryogenesis.
 External development allows
observation and manipulation of the
developing embryo.
 Large size allows study of
movement of cells within Xenopus
embryos
Germ layers and structural
Discoveries & Future Aspects:
 Spemann-Mangold organizer: First
discovered in amphibians, critical for
patterning the dorsal-ventral axis.
 Studies of cell fate determination:
Induction and differentiation.
 Discovery of key signaling
pathways: Wnt, BMP, and TGF-β.
Experimental Techniques:
Xenopus laevis (African Clawed Frog)
 Germ layers and structural
characteristics are easily observed.
Experimental Techniques:
 Microinjection of mRNA, morpholino
oligonucleotides, and CRISPR/Cas9.
 Fate mapping using dye-labeling
techniques.
Diffuse intemA.I
cytoplasm
Anlmal pole
Heavy yolk
plot.Jets
Vtg,tal pole

8. The Embryonic Signaling Center: Spemann's Organizer
 Classic experiment first performed by Spemann and Mangold in 1924
 Grafted dorsal lip of an embryo onto a second embryo
 Gastrulation initiated at both sites
 Second whole set of body structures formed
Double
embryo
develops with
nearly all its
tissues of host
origin
Dorsal lip of
blastopore
grafted
Cell fate studies in Xenopus: Noggin
 Noggin expression permits cells to become brain and nervous system
tissue
 No Noggin expression results in tissue becoming skin, bone
origin

9. Why Mouse?
 Mammalian model organism, with
high similarity to humans (~99% of
genes shared).
 Life cycle 9 weeks
 Genome sequenced
 Genetic manipulation well
developed.
Discoveries & Future Aspects:
 Gene knockout technology
pioneered here: Used to study the
function of specific genes.
 Martin Evans and Matthew established
embryonic stem cell technology in
mouse embryo. (Nobel Prize,2007)
 Models of human diseases: Cancer,
diabetes, neurological disorders.
Understanding of immune system
Mus musculus (Mouse)
 Understanding of immune system
development.
Applications:
 Mouse embryonic stem cell lines for
creating transgenic and knockout
mice.
 Models for human development, genetic
diseases, and therapeutic testing.

10. Why Arabidopsis?
 Model plant for studying genetics,
development, and physiology.
 Small genome (~125 Mb), fully
sequenced
 Short generation time (6 weeks).
Discoveries & Future Aspects:
 Floral development: ABC model of
flower development.
 Studies of photomorphogenesis (how
plants respond to light).
 Hormonal control of growth:
Auxins, cytokinins, and gibberellins.
Arabidopsis thaliana (Thale Cress)
Auxins, cytokinins, and gibberellins.
Applications:
Insights into crop improvement,
stress resistance, and plant-
pathogen interactions.

11. Why Sea Urchin?
 Pioneered understanding of
fertilization and early cleavage
stages.
 Transparent embryos and large size
made them ideal for early embryological
studies.
Key Contributions:
 Role of calcium waves in fertilization.
 Studies on developmental axes and
early cleavage patterns.
 Model for studying gene regulatory
networks during development.
Experimental Techniques:
In vitro fertilization, microinjection, live
imaging of calcium dynamics.
Sea Urchin
imaging of calcium dynamics.
Applications:
Insights into activation, and cell
division, embryogenesis, early
zygotic gene