Transcript Topic 1

BIOL 370 – Developmental Biology
Topic #1
Comprehending Development:
Generating New Cells and Organs
The focus in BIOL 370 – Developmental Biology is to
understand the physiological principles that guide
development in multicellular organisms.
This course will pull information from a wide array of
approaches to study biology including….
and cellular biology.
V.M. - Amphibian Life Cycle
Developmental history of the leopard frog, Rana pipiens
Embryogenesis – the stages of the life cycle from fertilization through hatching (or parturition in
Gametogenesis – the period of time(s) where germ cell lines are in production in some form
(Note that in the above, the purple color is showing times of strong germ cell development,
whereas the beige is showing times of strong somatic cell development.)
Heinz Christian Pander
Russian biologist, has been credited for the discovery of the three germ layers that form during
•Pander received his doctorate in zoology from the University of Wurzburg in 1817.
•He began his studies in embryology using chicken eggs, which allowed for his discovery of the
ectoderm, mesoderm and endoderm.
•Due to his findings, Pander is sometimes referred to as the "founder of embryology".
Early development of the frog Xenopus laevis
Amplexus – the mating behavioral
displayed by frogs where the male
will grasp the female around the
belly and deposit sperm onto eggs
as they are released.
a) Yolk is in green
b) Adults mating
c) Laid eggs
d – i) Development beyond the
fertilized egg
Continued development of Xenopus laevis
Continued development showing
a variety of stages.
i) – mature tadpole that has
hatched from the egg
Metamorphosis of the frog
Metamorphosis - biological
process by which an animal
physically develops after birth
or hatching that involves a
conspicuous and relatively
abrupt change in the animal's
body structure through cell
growth and differentiation.
Various insects, amphibians,
molluscs, crustaceans,
Cnidarians, echinoderms and
tunicates may undergo
Most examples of
metamorphosis are also
accompanied by a change in
habitat and/or behavior.
Summary of meiosis
In your review of meiosis, be sure to note the following:
Homologus chromosomes - chromosome pairs of the same length, centromere position,
and staining pattern, with genes for the same characteristics at corresponding loci. One
homologous chromosome is inherited from the organism's mother; the other from the
organism's father. They are not identical, but carry the same type of information.
Homologus chromatids - sister chromatids are generated when a single chromosome is
replicated into two copies of itself, these copies being called sister chromatids.
Summary of meiosis
The resulting production of gametes is the method by which sexually
reproducing species produce haploid cells that can be mixed together to
create offspring with greater genetic diversity than is seen in asexual
Depictions of chick developmental anatomy
When we examine chick development, we can see a variety of interesting
anatomical aspects.
Depictions of chick developmental anatomy (Part 1)
Classic Drawing by Malpighi (1672)
Depictions of chick developmental anatomy (Part 2)
Lillie, 1908
Depictions of chick developmental anatomy (Part 3)
Eduard d’Alton
Depictions of chick developmental anatomy (Part 4)
Dividing cells of the fertilized egg form three embryonic germ layers
As development progresses beyond the zygote and blastula, you see
greater differentiation in the gastrula stage.
Dividing cells of the fertilized egg form three embryonic germ layers (Part 1)
Differentiates to form the nervous
system (spine, peripheral nerves and
brain), tooth enamel and the
epidermis. It also forms the lining of
mouth, anus, nostrils, sweat glands,
hair and nails.
Dividing cells of the fertilized egg form three embryonic germ layers (Part 2)
Forms mesenchyme
(connective tissue),
mesothelium, blood cells and
coelomocytes (immune cells in
worms and spiders)
Mesothelium lines coeloms;
forms the muscles in a
process known as
Dividing cells of the fertilized egg form three embryonic germ layers (Part 3)
Parts of the alimentary canal), the
lining cells of all the glands which
open into the digestive tube,
general respiratory tract, the
trachea, bronchi, and alveoli,
general endocrine glands and
organs, parts of the auditory
system (the epithelium of the
auditory tube and tympanic
cavity), urinary system (the
urinary bladder and part of the
The notochord is an interesting structure that is seen only during
embryological development. In early development, it defines the
primitive axis of the embryo. In some chordates, it persists throughout
life as the main axial support of the body, while in most vertebrates it
becomes the nucleus pulposus of the intervertebral disc.
This image is showing a
computer enhanced image of
the vertebrate head (in this
case a salamander) early in
development. The purple
colored regions indicate what
are called:
Pharyngeal Arches
(Branchial Arches).
In the next slide, look at how
these structures develop into
various parts of the skeletal
bones of the head in different
Evolution of pharyngeal arch structures in the vertebrate head
Notochord in chick development
Notochord - guides development of of the
nervous system (neural tube/groove)
Somites – vertebrae, ribs, skeletal muscle.
Above – chick
To the right - frog
Similarities and differences among vertebrate embryos during development
Fate Maps and Cell Lineages:
Unlike in adults, the cells in the embryo tend to move and shift. Therefore, in
developmental biology it is cruicial to identify the following two types of cells:
Epithelial cells – cells that are very tightly connected to each other and form sheets
of tissue or tubes of tissue.
Mesenchymal cells – cells that ARE NOT connected to each other and function as
independent units.
Fate map for Drosophila sp. eggs.
Morphogenesis – a limited range of variations in processes of a cell within
epithelial and mesenchymal cells. Types of morphogenic variations include:
Direction and number of cell divisions
Additional morphogenic variations:
• Cell shape changes
• Cell migrations
• Cell growth
• Cell death – (programmed cell death is called apoptosis)
• Cell membrane changes
• Secretion changes by cells
Fate maps of vertebrates at the early gastrula stage
Fate Maps – maps of early developmental stages showing a tracing (or map) of
cell lineages through developmental time. Important for both descriptive and
experimental embryology.
Edwin Grant Conklin - traced the formation of organs to their
origins in the egg cell and embryo. Conklin also investigated the
physical mechanism of cell division.
Tunicates are marine filter feeders with a sac-like body structure. In their respiration
and feeding they take in water through an incurrent siphon and expel the filtered
water through an excurrent siphon.
Most adult tunicates are sessile and attached to rocks or similarly suitable surfaces
on the ocean floor.
Common names for specific examples of species of tunicates include sea squirts,
sea pork or sea tulips.
Fate map of the tunicate embryo
This diagram highlights two different
ways to represent a fate map…
b) Shows a cellular fate map
c) Shows a linear fate map
Walter Vogt - the first "fate map" of a vertebrate embryo -- a
description of how cells move from their original positions in the early
embryo to their ultimate destination.
Vital dye staining of amphibian embryos
Fate mapping using a fluorescent dye
A more modern take on Vogt’s approach:
Fluorescence Staining
Hilde Mangold
Embryologists who first successfully
transplanted embryonic tissues to
form chimeric embryos.
Hans Spemann
Chick resulting from transplantation of a trunk neural crest region from an embryo of a pigmented
strain of chickens into the same region of an embryo of an unpigmented strain
Genetic markers as cell lineage tracers
Two more modern takes on ’s Mangold & Spemans’s approach:
Genetic Markers
Genetic Markers
Fate mapping with transgenic DNA shows that the neural crest is critical in making the bones of the
frog jaw
Transgenic Labeling
Larval stages reveal the common ancestry of two crustacean arthropods
Similar Appearance Early On
Very Different Later
Homologies of structure among human arm, seal forelimb, bird wing, and bat wing
Development of bat and mouse
Selectable variation through mutations of genes that work during developmental
Developmental anomalies caused by genetic mutation
Piebaldism - a disorder caused by the KIT gene which regulates production
of the KIT protein which guides proliferation and migration of neural crest
cells among other cells.
Individuals affected often experience fertility issues, anemia, underpigmentation of skin and
hair, problems with the digestive systems and auditory issues.
Developmental anomalies caused by an environmental agent
Environmental exposure to chemicals can affect development in a myriad
of ways. The gentleman above was exposed to Thalidamide in-utero, and
this resulted in his phocomelia (insufficient limb growth).