Transcript Zoo 424 Lec 1 Introduction and review

‫بسم هللا الرحمن الرحيم‬
Zoo. (424)‫علم األجنة التجريبي‬
Principle Experimental Embryology
‫مقدمة ولمحة تاريخية‬
Introduction and Historical review
Principal of Experimental Embryology :
Introduction and historical review
• The embryology science reported by some verses of
the Quran in particular with regard to human creation
"so let man see, create, creation of water flush from between
back bone and ribs,(altraeb).... ‫خلق من ماء دافق خيرج من بني‬،‫فلينظر الإنسان مما خلق‬
‫ "الصلب والرتائب‬Yes it is God sinah in this life,
• All multicellular organisms arose from the mating
between male and female gametes (fertilization)
• Note the embryos in different developmental stages
from gamete to cleavage (from Zygote to blastula
stage).
• Then Gastrulation stage, the formation of the three
different embryonic layers, ectoderm,mesoderm and
endoderm(gastrula).
• Later the organogensis stage: from these 3
embryonic layers were all the organs of the embryo
will form.
• Finally the grow and increase in size until the exit of
the embryo for life (hatching or birth).
Introduction :The development of multicellular organisms from a
single cell—the fertilized egg—is a brilliant thinking .
During embryonic development, the egg divides to give rise to many
millions of cells ,which form structures as complex and varied as eyes,
arms, heart, and brain. This amazing achievement raises many questions.
-How do the cells arising from division of the fertilized egg become
different from each other?
-How do they become organized into structures such as limbs and brains?
- What controls the behavior of individual cells so that such highly
organized patterns emerge? -How are the organizing principles of development
embedded within the egg, and in particular within the genetic material, DNA?
-Much of the excitement in developmental biology today comes from our
growing understanding of how genes direct these developmental processes,
and genetic control is one of the main themes of this course.
-Several of factors are involved in controlling development, but we will
focus only on those that have key roles and illustrate general principles.
-The development of an embryo from the fertilized egg is known as
embryogenesis. One of its first tasks is to lay down the overall body plan of
the organism, and we shall see that different organisms solve this fundamental
problem in several ways.
Branches of Embryology
Embryology has many sub-branches in it. They are:• 1- Descriptive Embryology
• It is applied to the method of study concerned with the direct
observation and description of embryological development.
Embryology in ancient times started as a branch of study
based on the direct observation and description by scientists
like Aristotle (340 B.C.), Fabricius (1537 – 1619), Harvery
(1578 – 1657) and so on.
• 2- Comparative embryology
• It is the embryological development of different animals and
studied and compared. Comparative embryology throws
much light on the understanding of evolution and
phylogenetic significance. It also give some ideas on the
developmental stages of certain animals in whose case the
study of development is different.
• 3- Experimental Embryology
• In it is experiments are used for studying the
developmental stages. It helps to understand the
fundamental developmental mechanisms. In
experimental embryology the various parts of
developing embryo are removed, transplanted,
parts exchanged or the environmental conditions
altered. This helps to understand induction,
gradient system, etc. Experimental embryology
is also called casual embryology of analytical
embryology. Roux (1850 – 1924) is the pioneer
in the field of experimental embryology.
4- Chemical Embryology
The developmental stages are studied by biochemical
and physiological techniques. It is also called
physiological or biochemical embryology. Needham
(1931) is the pioneer in this field.
5- Teratology
It is a branch of embryology concerned with the study
of malformations or abmormal development.
6- Developmental Biology
It includes not only embryonic development but also
postnatal processes such as normal and neoplastic
growth, metamorphosis, regeneration and tissue
repair in both animal and plant .
Historical and background of Exp. Embryology
Aristotle (384 – 322 B.C ): Before the 17th century embryological
knowledge was based on the writings of Aristotle and Galen.
Embryology as a branch of biology was initiated by the famous Greek
philosopher Aristotle (384 – 322 B.C.).
He was the first embryologist to describe the development and
reproduction of many kinds of organisms in his book entitled
"Degeneratione Animalium". He believed firmly that the complex adult
organism develops from a simple formless beginning.
Thus he laid the foundation for the basic principles of epigenesist, a theory
postulated after 2000 years. For this Aristotle is honored as the father
of embryology. Aristotle has written that the male contributes the semen
and the female contributes the contamenia. The semen is secreted by
testis and it is hot and active. The catamenia is carried through very fine
vessels into the uterus. It is equivalent to the menstrual blood. He had
no knowledge of ovary. He thought that the female reproductive system
is formed of uterus only and not of anything else.
Cont .Historical and background of Embryology
Wilhelm Roux (1888)and Hans Driesch (1892) both
In separate experiments, Wilhelm Roux (1888) and
Hans Driesch (1892) set out to determine whether
epigenesis or preformation was correct. Both allowed
a fertilized egg to divide to the two-cell stage. Roux,
using amphibian embryos (frogs, toads,
salamanders), killed one of the two cells with a hot
needle. Driesch, using echinoderm embryos (sea
stars, sea urchins, sea cucumbers), completely
separated the divided cells. An entire animal
developing from a single cell would support
epigenesis. A portion of the animal developing would
favor preformation. What was the result?
Interestingly, Roux described the formation of a half
embryo that he called a “hemiembryo” (figure a), and
Driesch found that each cell retained the potential to
develop into an entire organism (figure b).
August Weismann 1880s propose that the germ plasma
theory: The egg and sperm contribute chromosomes
equally to the zygote (fertilized egg). The chromosomes
are carriers of the hereditary potentials, and the germ
cells (gametes) of the embryo are the only ones to carry
the complete set of hereditary potentials (nuclear
determinants), whereas each somatic (body) cell type
contains only part of these potentials required for the
specific cell type.
• Oscar Hertwig (1872)
• He repeat the Wilhelm's experiments, but he separate
the 2 cell frog embryo from them and improved that each
cell had a potential to grow, but the embryo result is half
size than normal embryo. This experiment is considered
the one of explanations of twins formation result from
one egg.
• Theodor Boveri (1902)
• He studied the effect of nucleus and cytoplasm on the
development of the sea urchin fertilized ovum by study of
controls and filaments formation during different division
stages. Also, he tries to insemination of specific species
ovum with another species sperm, and he found that the
chromosomes are different in quantity and numerically.
•
Thomas Hunt Morgan (1866 – 1945)
• He is the first scientist that suggested that the embryonic
development is controlled by expressions of different
genes, and he awarded Nobel prize for discovered the
mutations in Drosophila and their role in understand the
role of genes in heredity.
• Otto Warburg (1908 – 1910)
• He studied the respiratory mechanism in sea urchin
embryo cells, and he considers the first scientist who
definition oxygen consumes in respiratory of ovum and
embryonic cells. Their study resulted in know that the
fertilization make to increase the cellular reparatory rate
of fertilized ovum. So, he discovered the cytochrome
Oxidase and he awarded the Nobel prize on this
discovery at 1931.
Ernest E. Just (1883 – 1941)
• He descriptive the changes occurred around the oocytes during
the fertilization in sea urchin and he studied the
parthenogenesis to understand the relationship between
penetrate of sperm and the first division of Nematoda oocytes.
• Viktor Hamburger (1954)
• The discovery of chick embryo's neural sector. Hamburger
proposed an antiapoptotic action of the hypothetical targetderived trophic signals, identified as nerve growth-stimulating
factor, later named nerve growth factor (NGF).
• Ross Granville Harrison (1870 – 1975)
• He successfully cultured frog neuroblasts in a lymph medium
and thereby took the first step toward current research on
precursor and stem cells. He was considered for a Nobel prize
for his work on nerve-cell outgrowth, which helped form the
modern functional understanding of the nervous system, and he
contributed to surgical tissue transplant technique.
• Hans Spemann and Mangold (1924)
• Hilde Mangold’s experiment involved taking a piece of
the lip of the blastopore of the gastrula stage of the
amphibian embryo and grafting it to the wall (flank) of
another gastrula at a site distant from the host
blastopore, and thereby induced a secondary axis of
polarity in the host that eventually developed into a
secondary embryo.
• In 1935 Spemann received the Nobel Prize for
Medicine or Physiology as the first embryologist.
• Jean Brachet (1988 – 1909)
• In 1933 Brachet was able to show that DNA was found in
chromosomes and that RNA was present in the cytoplasm of all
cells. His work showed that RNA plays an active role in protein
synthesis. Brachet also carried out pioneering work in the field
of cell differentiation. Brachet later demonstrated papers that
differentiation is preceded by the formation of new ribosomes
and accompanied by the release from the nucleus of a wave of
new messenger RNA.
• Robert Briggs (1983 – 1911) and Thomas Joseph King
• He was a scientist who in 1952, together with Thomas Joseph
King, cloned a frog by nuclear transfer of embryonic cells.
• The same technique, using somatic cells, was later used to
create Dolly the Sheep by Willmut and Kith Kamble 1997 . Their
experiment was the first successful nuclear transplantation
performed in metazoans.