Download BIO706 Lecture # 1 File

Faculty of Science, School of
Sciences, Natabua Campus
Lautoka
BIO706 Embryology
Lecture 1: History of Embryology
Developmental Biology
The past is full of ideas about how
organisms developed and where
they came from?
These range from pure magic
To cultural myths
To flights of fantasy
And, in recent times,
To observational and experimentally based
inquiry
Questions?
Where are the plans or instructions for development?
How are they interpreted and used?
Where are the raw materials for development?
How did those raw materials get to the embryo?
How are they used?
How do different cells and tissues know what to become?
How do cells migrate? How do they know where to go?
How is neural circuitry established?
How do axons find their targets?
Etc., etc, etc.
One important thing to keep
in mind,
Development DOES NOT
happen by magic.
Information and mechanisms
at the cellular and/or molecular
levels are needed to
accomplish development
Developmental Biology is Defined
by
•
•
•
•
•
•
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental Integration
Developmental Biology is Defined by
•
•
•
•
•
•
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental
Integration
What goes on as an
embryo develops from a
single, pluripotent cell
into a complete
organism?
Majority of
developmental systems
are multicellular
Single-celled systems used
to study cellular
differentiation
Developmental Biology is Defined by
•
•
•
•
•
•
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental
Integration
Cell movements & tissue
reorganizations
How do differentiated
cells move and
reorganize during
development to
generate functional
organisms?
Major point of study for
classical embryology
Developmental Biology is Defined by
•
•
•
•
•
•
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental
Integration
What are the limiting
factors for cell division
Allometric growth - varying
rates of mitosis in regions
of the embryo
Isometric growth- equal
rates of mitosis
throughout embryo
Developmental Biology is Defined by
• Differentiation
• Morphogenesis
• Growth
• Reproduction
• Evolution
• Environmental
Integration
The germplasm
Gametogenesis formation and
maintenance of
pluripotent, haploid
germ cells (gametes)
Recognition &
interaction of gametes
at fertilization
Developmental Biology is Defined by
Survivability of evolutionary
• Differentiation
mutations is limited by
• Morphogenesis restraints of
embryogenesis
• Growth
Evolutionary changes must
• Reproduction
be small changes for the
• Evolution
embryo
• Environmental What are the evolutionary
relationships between
Integration
groups of organisms
Developmental Biology is Defined by
•
•
•
•
•
•
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental
Integration
Early development of
many organisms is
influenced by
environmental cues
Examples:
color/shape of
butterfly larvae
(caterpillars)
Early Embryologist
Many of the ancient Greek Philosophers were interested
in embryology
Democritus (ca. 455-370BC): the sex of an individual is
determined by the origin of sperm; Male arise from the
right testicle and female from left.
This hypothesis modified by Phythagoras, Hippocartes
and Galen, however gender bias was always evident, For
science was the privilege of men; Philosophers mostly
positioned female between Men and Animals, So males
were supposed to originated from stronger sperm of
right testicle.
Early Embryologist
Greek Philosopher Aristotle in Generation of Animals ca.
350 BC
Suggested the different ways that animals are born
From Egg: (Oviparity Eg. Birds, Frogs and Most
Invertebrates)
From Life Birth: (Viviparity Eg. In placental animals and
some fish)
By production of an egg that hatches inside the body:
(Ovoviviparity Eg. Certain reptiles and sharkes)
Aristotle considered two basic
developmental questions:
Do all parts of a developing organism
come into existence together and
simply grow larger?
or
Is development a stepwise process
characterized by progressive
organization and an increase in
complexity?
Preformation versus Epigenesis
Preformation –
The organism is
preformed as a complete
miniature structure in the
sperm or the egg and
simply grows larger as it
develops. This means
that the first reproducing
human would have had to
have all succeeding
generations within itself..
Epigenesis
The organism
develops in a
stepwise fashion
from an
unorganized state.
Aristotle believed that the embryo was
formed from the menstrual blood as a
result of that blood’s interaction with a
male factor, called the male dynamic,
that was present in the semen.
His observations supported the
concept of epigenesis, though
this term would not be used until
the mid to late 17th century.
Greek Philosopher Aristotle noted two major
pattern of cell division in early development
Holoblastic cleavage
(Entire egg is divided into progressively
smaller cells E.g. Frogs, Mammals)
Meroblastic pattern
( In which only that part of egg destined to
become the embryo proper divides, with the
remainder serving nutritive purpose E.g.
Birds)
Mid 17th century - 18th century
Epigenesis vs Preformation - a matter for debate
Preformationists
Spermists vs ovists
Jan Swammerdam ~ 1672
Spermists - contended
Nicholas Malebranche ~1673 that sperm contained the
new individual in
Nicolas Hartsoeker ~ 1694
miniature and only
Charles Bonnet ~ 1762
nourished in the ovum
Ovists- thought the same
Epigeneticists
way about the ovum and
William Harvey ~ 1651
stimulated only in the
Rene Descartes ~ 1664
seminal fluid.
Marcello Malpighi ~ 1672
Pierre Maupertuis ~ 1745
Preformationists
.
SPONTANEOUS GENERATION
Recipe for bees:
Kill a young bull, and bury it in an
upright position so that its horns
protrude from the ground. After a
month, a swarm of bees will fly out of
the corpse.
Preformationists
Jan Baptista van Helmont’s recipe for
mice:
Place a dirty shirt or some rags in an open
pot or barrel containing a few grains of
wheat or some wheat bran, and in 21
days, mice will appear. There will be adult
males and females present, and they will
be capable of mating and reproducing
more mice.
Preformationists
Jan Swammerdam, ~1672 : 17th century
Dutch microscopist
Debunked “Spontaneous generation” using
meticulous dissections and careful
experimentation.
Thought to have originated the idea of
Preformation
Greatest contribution to science demonstrated that in insect development,
the same organism persists through
various stages, i.e. larva, pupa, juvenile,
adult.
Preformationists
Marcelo Malpighi, ~1672
Professor of medicine and personal physician to Pope
Innocent XII
Early microscopist
One of the first scientists to study structures such as the
lungs, kidneys, spleen, brain, and skin
Because of the importance of his early work a number of
anatomical structures still bear his name - Malpighian
corpucles (renal corpuscle) in kidney, Malpighian layer in
epidermis of skin Malpighian tubules in insects
Marcello Malpighi - did not believe what was right before his
eyes when examining chicken development: identify the neural
groove, the somites and circulation of blood in arteries and
veins to and from yolk with the microscope.
Preformationists
Nicolas Hartsoeker, ~1694
Dutch mathematician and
physicist
Invented the screw-barrel
microscope
Co-discoverer of sperm
and claimed to be able to
see a tiny human –a
homunculus- in the head
of each human sperm..
The
homunculus
Preformationists
Charles Bonnet, ~1762
Swiss lawyer, naturalist, philosopher
Ovist - from studies of parthenogenesis in Daphnia - felt
that the theory of preformation was “…one of the
greatest triumphs of rational thought over sensual
conviction.”
In Philosophical Palingests, or Ideas on the Past and
Future - argued that females carry within them all future
generations in miniature form.
Comment on the preformation paradox:
“…it is always possible, by adding zeros, to crush the
imagination under the weight of numbers.”
Epigeneticists
William Harvey, ~1651
Physician to King Charles I of England
In 1628 Harvey published An Anatomical Study of
the Motion of the Heart and of the Blood in
Animals which explained how blood was pumped
from the heart throughout the body, then
returned to the heart - recirculation of blood.
Also published Essays on the Generation of
Animals - considered the foundation for modern
embryology
Epigeneticists
Rene Descartes, ~1664
Philosopher, physicist, physiologist and
mathematician – famous in all.
Considered one of the most important and
influential thinkers in human history.
Cogito ergo sum - “I think, therefore I am.”
“If you would be a real seeker after truth, it is
necessary that at least once in your life you
doubt, as far as possible, all things.”
Epigeneticists
Pierre Maupertuis, ~1745
French mathematician and biologist
In Essai de cosmologie - introduced the
theory of survival of the fittest.
Argued that preformation could not account
for hybrids or “congenital monsters”
Proposed that the embryo goes through a
number of distinct developmental stages.
What’s the correct answer, epigenesis or
preformation?
Neither is totally correct as originally stated;
however, there’s some truth to both, though not
in the context of 17th and 18th century thought.
Epigenesis - in that development does occur
gradually in a stepwise progression moving
from a single cell to a multicellular organism of
increasing complexity (however, development
does not start out from an unorganized state,
the zygote is highly organized at the cellular and
molecular level).
Preformation - in that the instructions for
development are present “preformed” in
the zygote - genes (DNA).
The preformation/epigenesis issue was
the subject of vigorous debate
throughout the 18th century. But the
problem could not be resolved until
one of the great advances in biology had
taken place-the recognition that
living things, including embryos, were
composed of cells.
Cell theory of development
The cell theory developed between 1820 and
1880 by, the German botanist Matthias
Schleiden and the physiologist Theodor
Schwann.
It was at last recognized that all living organisms
consist of cells, which are the basic units of life,
and which arise only by division from other cells.
Multicellular organisms such as animals and plants
could then be viewed as communities of cells.
Development could not therefore be based on
preformation but must be epigenetic,
An important advance was the proposal by
the 19th century German biologist August
Weismann that the offspring does not inherit
its characteristics from the body (the soma)
of the parent but only from the germ cells-egg
and sperm-and that the germ cells are not
influenced by the body that bears them.
Weismann thus drew a fundamental
distinction between germ cells and somatic
cells or body cells
The distinction between germ cells and somatic cells.
In each generation germ cells give rise to both somatic
cells and germ cells, but inheritance is through the germ
cells only
In 19th century an experiment on sea urchin
eggs showed that after fertilization the egg
contains two nuclei, which eventually fuse;
one of these nuclei belongs to the egg while
the other comes from the sperm.
Fertilization therefore results in an egg
carrying a nucleus with contributions from
both parents, and it was concluded that
the cell nucleus must contain the physical
basis of heredity.
The climax of this line of research was the
eventual demonstration, toward the end of the
19th century, that the chromosomes within
the nucleus of the zygote (the fertilized egg)
are derived in equal numbers from the two
parental nuclei, and the recognition that this
provided a physical basis for the transmission
of genetic characters according to laws
developed by the Austrian botanist and monk
Gregor John Mendel.
The coming together of genetics and
development
Genetics was seen
as the study of the
transmission of
hereditary elements
from generation to
generation
Embryology was the
study of how an
individual organism
develops and, in
particular, how cells
in the early embryo
became different
from each other.
Danish botanist Wilhelm Johannsen in 1909
put forward a concept to link genetics and
embryology was distinction between
genotype and phenotype
The genetic endowment of an organismthe genetic information it acquires from
its parents-is the genotype. Its visible
appearance, internal structure, and
biochemistry at any stage of development is
the phenotype.
The discovery in the 1940s that genes
encode proteins was a major turning point.
As it was already clear that the properties of
a cell are determined by the proteins it
contains, the fundamental role of genes in
development could at last be appreciated.
By controlling which proteins were made
in a cell, genes could control the changes
in cell properties and behavior that occurred
during development.
Questions are welcome