The Origin of Developmental Biology

BYZeinab SalahDalia Ahmed

The Origin of Developmental Biology

BYZeinab SalahDalia Ahmed

Definition

• Developmental biology is the branch of life

science, which deals with the study of the process

by which organisms grow and develop and which

the genes in the fertilized egg control cell behavior

in the embryo and so determine its pattern, its form,

and much of its behavior.

• It is an integration of embryology ( the study of

embryonic development) with cytology (the study of

cellular structure and function) and later with genetics

(the study of inheritance).

• Modern developmental biology studies the genetic

control of cell growth, differentiation and

"morphogenesis," which is the process that gives rise to

tissues, organs and anatomy.

Historical background

Hippocrates in 5th century BC ;

He tried to explain development in terms of the

principles of heat, wetness, and solidification.

Aristotle;

Established ‘embryology’ as an independent field .

Defined epigenesis and preformation.

.

• Preformation theory suggests that all structures

exist from the very beginning, they just get larger.

• Epigenesis (~upon formation) is a theory of

development that states that new structures arise by

progressing through a number of different stages.

• Marcello Malpighi in 17th century :

• Italian embryologist.

• He provided a remarkably accurate description of the

development of the chick embryo.

• He argued that at the very early stage the parts were so

small that they can not observed even by his best

microscope.

• Mathais Schleiden and Theodor Schwann

(1838-39) ;

• Developed the Cell Theory.

• This theory is one of the foundations of biology. The

theory says that new cells are formed from other existing

cells, and that the cell is a fundamental unit of structure,

function and organization in all living organisms.

• August Weismann (1834 – 1914);

• German evolutionary biologist.

• Weismann's theory of inheritance

• Proposed that the sperm and egg provided equal

chromosomal contributions, both quantitatively and

qualitatively, to the new organism. Moreover, he postulated

that the chromosomes carried the inherited potentials of

this new organism and hypothesized that only the germ

cells contained all the inherited determinants.

•Mosaic development depends upon specific determinants in the one-celled zygote that are not divided equally between the daughter cells (asymmetric division).

• Wilhelm Roux (1888) ;

• German embryologist.

• He support weismann’s theory by experiments in frog

embryos, he destroyed one of the two cells with hot

needle and then result into well –formed half larva.

Early evidence for mosaic development

• He concluded that the frog embryo was a mosaic of

self-differentiating parts and that it was likely that each

cell received a specific set of determinants and

differentiated accordingly.

• Hans Driesch( 1892);

• Demonstrate regulative development which depends

upon interactions between 'parts' of the developing

embryo can result in causing different tissues to form

(even if parts of the original embryo are removed).

Driesch destroyed one cell of a sea urchin embryo at the

two cell stage and a normal appearing but smaller sea

urchin larvae resulted.

Sea Urchin Embryos show regulative Development

• So is development mosaic or

regulative?

• A. It is a combination of both

• Hans Spemann and Hilde Mangold;

• Discovery of primary Embryonic Induction.

• Induction is a type of regulatory development.

• They proved the importance of induction and other cell-cell

interactions in development by transplant experiment in

amphibian embryos.

Spemann and Mangold transplanted dorsal lip of the blastopore to a different blastula and a new main body axis developed.

• Gregor Mendel's;

• In 1900, the significance of Gregor Mendel's

work on heredity was finally appreciated.

• Mendel was the first scientist to develop a

method for predicting the outcome of

inheritance patterns.

• He is the father of modern genetics for his

study of the inheritance of traits in pea plants.

• Mendel showed that the inheritance of traits

follows particular laws, which were later

named after him.

Theodor Boveri;

German biologist.

Had major support for the chromosomal hypothesis of inheritance.

One of the biologists who felt that the nucleus contained the

instructions for development who in a paper published in 1902

demonstrated that normal development is dependent upon the

normal combination of chromosomes.

• .

• Thomas Hunt Morgan

• American geneticist and embryologist.

• Noted in 1926 that the only way to get from genotype to

phenotype is through developmental processes.

• Morgan redefined genetics as the science studying the

transmission of traits, as opposed to embryology, the

science studying the expression of traits.

He able to combine genetics with developmental biology and

create the discipline of developmental genetics.

Morgan had shown that nuclear chromosomes are

responsible for the development of inherited characters.

The final proof of the chromosome theory of inheritance

resulted from research using the fruit fly, Drosophila

melanogaster that was conducted in Thomas Hunt Morgan's

laboratory at Columbia University.

Animal Development

Animal Development

• Summarize the basic steps in animal develop

starting gametogenesis and ending with death.

• GAMETOGENESIS

– Specialization of ovum and sperm

• FERTILIZATION

– Block of polyspermy

• CLEAVAGE

– Cell division without an increase in total volume

• MORULA

– Solid mass of cells

• BLASTULATION

– Hollow mass of cells

5 Processes of  Development

1. Cleavage Division: 

No increase in cell mass

2. Pattern Formation: 

A/P(anterior head/ posterior tail) and D/V axes(Dorsal upper or

back/Ventral lower or front): Coordinate system

3. Morphogenesis: 

take 3D form.

.

4. Cell Differentiation: 

cells become structurally and functionally

different.

5. Growth: 

cell multiplication, increase in cell size, deposit

extracellular material (bone, shell) growth can be

morphogenetic

• Developmental model organisms

• Vertebrates

– Zebrafish Danio rerio

– Frog Xenopus laevis, Xenopus tropicalis

– Chicken Gallus gallus

– Mouse Mus musculus

• Invertebrates

– Roundworm Caenorhabditis elegans

– Fruit fly Drosophila melanogaster

The developmental-genetic toolkit

• Consists of genes whose products control the

development of a multicellular organism.

• The majority of toolkit genes are components of

signaling pathways, and encode for the production

of transcription factors, cell adhesion proteins, cell

surface receptor proteins, and secreted

morphogens.

• The most important toolkit genes are those of the Hox gene

cluster.

• Mutations in any one of these genes can lead to the growth of

extra, typically non-functional body parts in invertebrates, for

example aristapedia complex in Drosophila, this mutation is

known as Antennapedia.

• The genes that regulate development are best understood in

two species, the mouse

• and the fruitfly

HOMOLOGOUS HOX SEQUENCES:EXPRESSION

HOMOLOGOUS HOX GENES: DERIVATION

MUTATIONS INREGULATORY GENES CAN GIVE THE PROTEINS NEWPROPERTIES: UBXACQUIRES THE ABILITY to REPRESS DISTAL-LESS in the INSECT CLADE

Evolutionary developmental biology

• “Evolution is a change in the genetic composition of populations.

• The study of the mechanisms of evolution falls within the province

of population genetics.” Theodosius Dobzhansky. 1951

Evolutionary developmental biology

• The emergence of new phenotypes is made

possible by changes in development. The regulatory

genes that have long been thought to control the

generation of novel structures are now being

discovered

• Evolutionary developmental biology, now often

known as “evo-devo,” is the study of the relation

between evolution and development. The relation

between evolution and development has been the

subject of research for many years, However, the

subject has been transformed in recent years as the

genes that control development have begun to be

identified.

The Modern Era

• The Impact of Molecular and Cellular Biology

• The molecular biology revolution in the middle of the

Twentieth Century provided the means to study the

role of genes in development that Wilson and his

contemporaries lacked. The key technological advance

for the study of gene control of development was the

ability to isolate and clone genes.

• Much of the current research in developmental

biology involves attempts to understand the cellular

and intercellular events that signal the nucleus to

express genes or initiate a sequence of gene

expression.

There are two powerful techniques allow investigators

to test directly the roles of specific genes during

development:-

• Introduce cloned genes into embryos and assess

their effects on development.

• Eliminate or "knock out" specific genes and

determine the effects on development.

THANK YOU

References

• Developmental biology 6th edition. Gilbert