DIFFERENT STAGES OF DROSOPHILA DEVELOPEMENT

1. S.o.s in Biotechnology
Topic – Development in drosophila
Guided by :-
Dr. Jay Shankar Paul
Submitted by :- P. Sujata
Msc I sem

2. Content
 Drosophila introduction
 Drosophila life cycle
 Drosophila development
 Fertilization
 Cleavage
 Gastrulation
 Egg polarity genes
 Dorsal - ventral axis
 Anterior – posterior axis
 Segmentation genes
 Homeotic genes
 Mutation in drosophila
 Drosophila in genetic analysis

3.  Drosophila is a species of a fruit fly in the family
drosophilidae.
 The species is known generally as the common
fruit fly or vinegar fly.
 A wild drosophila or fruit fly has multi-faced
brick red eyes, a thorax with arched black
bristles, a striped abdomen and a pair of
translucent wings.
 The thorax consists of three segments.
 The fly’s rapid life cycle lo chromosome number ,
small genome size, and giant salivary glands
have many experimental advantages.

4.  When a Drosophila egg has been fertilized, its diploid nucleus
immediately divides nine times without division of the cytoplasm,
creating a single, multinucleate cell
 These nuclei are scattered throughout the cytoplasm but later
migrate toward the periphery of the embryo and divide several
more times .
 Next, the cell membrane grows inward and around each nucleus,
creating a layer of approximately 6000 cells at the outer surface of
the embryo
 Nuclei at one end of the embryo develop into pole cells, which
eventually give rise to germ cells.
 The early embryo then undergoes further development in three
distinct stages:
 the anterior–posterior axis and the dorsal–ventral axis of the embryo are
established
 the number and orientation of the body segments are determined
 the identity of each individual segment is established Different sets of genes
control each of these three stages.

6. Drosophila development
 Drosophila develop a holometabolous
method of development.
 They have three distinct stages of
their life cycle with different body
plans: larva , pupa and adult (imago).
 Drosophila development is orderly
sequence of change which is
controlled by different genes .

7. Drosophila development - overview
 Fertilization
 Cleavage
 Gastrulation
 Drosophila body plan
Egg polarity genes
Doral – ventral axis
Anterior posterior axis
 Segmentation genes
 Homeotic gens

8. Fertilization

9. Cleavage

12. Drosophila body plan
Egg polarity genes
 The egg-polarity genes play a crucial role in establishing the
two main axes of development in fruit flies.
 You can think of these axes as the longitude and latitude of
development: any location in the Drosophila embryo can be
defined in relation to these two axes.
 The egg-polarity genes are transcribed into mRNAs in the
course of egg formation in the maternal parent, and these
mRNAs become incorporated into the cytoplasm of the egg.
 After fertilization, the mRNAs are translated into proteins that
play an important role in determining the anterior–posterior
and dorsal–ventral axes of the embryo.
 Because the mRNAs of the polarity genes are produced by
the female parent and influence the phenotype of the
offspring, the traits encoded by them are examples of genetic
maternal effects

13.  There are two sets of egg-polarity genes: one set determines the
anterior–posterior axis, and the other determines the dorsal–ventral
axis.
 These genes work by setting up concentration gradients of
morphogens within the developing embryo.
 A morphogen is a protein that varies in concentration and elicits
different developmental responses at different concentrations.
 Egg-polarity genes function by producing proteins that become
asymmetrically distributed in the cytoplasm, giving the egg polarity, or
direction.
 This asymmetrical distribution may take place in a couple of ways. An
mRNA may be localized to particular regions of the egg cell, leading to
an abundance of the protein in those regions when the mRNA is
translated.
 Alternatively, the mRNA may be randomly distributed, but the protein
that it encodes may become asymmetrically distributed by a transport
system that delivers it to particular regions of the cell, by regulation of
its translation, or by its removal from particular regions by selective
degradation

14.  The dorsal–ventral axis defines the back (dorsum) and belly (ventrum) of
a fly (see At least 12 different genes determine this axis, one of the most
important being a gene called dorsal.
 The dorsal gene is transcribed and translated in the maternal ovary, and
the resulting mRNA and protein are transferred to the egg during
oogenesis. In a newly laid egg, mRNA and protein encoded by the dorsal
gene are uniformly distributed throughout the cytoplasm but, after the
nuclei have migrated to the periphery of the embryo .
 Dorsal protein becomes redistributed. Along one side of the embryo,
Dorsal protein remains in the cytoplasm; this side will become the dorsal
surface. Along the other side, Dorsal protein is taken up into the nuclei;
this side will become the ventral surface.
 At this point, there is a smooth gradient of increasing nuclear Dorsal
concentration from the dorsal to the ventral side .
 The nuclear uptake of Dorsal protein is thought to be governed by a
protein called Cactus, which binds to Dorsal protein and traps it in the
cytoplasm.
 The presence of yet another protein, called Toll, leads to the
phosphylation of Cactus, causing it to be degraded. When Cactus is
degraded, Dorsal is released and can move into the nucleus.

15.  Cactus and Toll regulate the nuclear distribution of
Dorsal protein, which in turn determines the dorsal–
ventral axis of the embryo. Inside the nucleus, Dorsal
protein acts as a transcription factor, binding to
regulatory sites on the DNA and activating or
repressing the expression of other genes
 High nuclear concentration of Dorsal protein (as in
cells on the ventral side of the embryo) activates a
gene called twist, which causes ventral tissues to
develop.
 Low nuclear concentrations of Dorsal protein (as in
cells on the dorsal side of the embryo), activate a
gene called decapentaplegic, which specifies dorsal
structures.
 In this way, the ventral and dorsal sides of the
embryo are determined

17.  One of the most important early developmental events is the determination of the
anterior (head) and posterior (butt) ends of an animal.
 We will consider several key genes that establish this anterior–posterior axis of the
Drosophila embryo
 An important gene in this regard is bicoid, which is first transcribed in the ovary of
an adult female during oogenesis. The bicoid mRNA becomes incorporated into the
cytoplasm of the egg; as it passes into the egg, bicoid mRNA becomes anchored to
the anterior end of the egg by part of its 3′ end. This anchoring causes bicoid mRNA
to become concentrated at the anterior end number of other genes that are active
in the ovary are required for proper localization of bicoid mRNA in the egg.) When
the egg has been laid, bicoid mRNA is translated into Bicoid protein.
 Because most of the mRNA is at the anterior end of the egg, Bicoid protein is
synthesized there and forms a concentration gradient along the anterior–posterior
axis of the embryo, with a high concentration at the anterior end and a low concen
tration at the posterior end.
 This gradient is maintained by the continuous synthesis of Bicoid protein and its
short half-life.
 The high concentration of Bicoid protein at the anterior end induces the
development of anterior structures such as the head of the fruit fly. Bicoid—like
Dorsal—is a morphogen.
 It stimulates the development of anterior structures by binding to regulatory
sequences in the DNA and influencing the expression of other genes.
 One of the most important of the genes stimulated by Bicoid protein is hunchback,
which is required for the development of the head and thoracic structures of the
fruit fly.

18.  The development of the anterior–posterior axis is also greatly influenced
by a gene called nanos, an egg-polarity gene that acts at the posterior
end of the axis. The nanos gene is transcribed in the adult female, and
the resulting mRNA becomes localized at the posterior end of the egg .
 After fertilization, nanos mRNA is translated into Nanos protein, which
diffuses slowly toward the anterior end.
 The Nanos protein gradient is opposite that of the Bicoid protein: Nanos
is most concentrated at the posterior end of the embryo and is least
concentrated at the anterior end.
 Nanos protein inhibits the formation of anterior structures by repressing
the translation of hunchback mRNA.
 The synthesis of the Hunchback protein is therefore stimulated at the
anterior end of the embryo by Bicoid protein and is repressed at the
posterior end by Nanos protein.
 This combined stimulation and repression results in a Hunchback protein
concentration gradient along the anterior–posterior axis that, in turn,
affects the expression of other genes and helps determine the anterior
and posterior structures.

20.  Like all insects, the fruit fly has a segmented body plan. When the basic dorsal–ventral and
anterior–posterior axes of the fruit-fly embryo have been established, segmentation genes
control the differentiation of the embryo into individual segments.
 These genes affect the number and organization of the segments, and mutations in them usually
disrupt whole sets of segments.
 The approximately 25 segmentation genes in Drosophila are transcribed after fertilization; so
they don’t exhibit a genetic maternal effect, and their expression is regulated by the Bicoid and
Nanos protein gradients.
 The segmentation genes fall into three groups. The three groups of genes act sequentially,
affecting progressively smaller regions of the embryo.
 First, the products of the egg-polarity genes activate or repress gap genes, which divide the
embryo into broad regions.
 The gap genes, in turn, regulate pair-rule genes, which affect the development of pairs of
segments. Finally, the pair-rule genes influence segment-polarity genes, which guide the
development of individual segments. Gap genes define large sections of the embryo; mutations
in these genes eliminate whole groups of adjacent segments.
 Mutations in the Krüppel gene, for example, cause the absence of several adjacent segments.
Pair-rule genes define regional sections of the embryo and affect alternate segments.
 Mutations in the even-skipped gene cause the deletion of even-numbered segments, whereas
mutations in the fushi tarazu gene cause the absence of odd-numbered segments. Segment-
polarity genes affect the organization of segments.
 Mutations in these genes cause part of each segment to be deleted and replaced by a mirror
image of part or all of an adjacent segment. For example, mutations in the gooseberry gene
cause the the posterior half of each segment to be replaced by the anterior half of an adjacent
segment.

22.  After the segmentation genes have established the number and orientation of the
segments, homeotic genes become active and determine the identity of individual
segments.
 Eyes normally arise only on the head segment, whereas legs develop only on the
thoracic segments.
 The products of homeotic genes activate other genes that encode these segment-
specific characteristics. Mutations in the homeotic genes cause body parts to appear
in the wrong segments. In the late 1940s, Edward Lewis began to study homeotic
mutations in Drosophila—mutations that cause bizarre rearrangements of body
parts.
 Mutations in the Antennapedia gene, for example, cause legs to develop on the head
of a fly in place of the antenna Homeotic genes create addresses for the cells of
particular segments, telling the cells where they are within the regions defined by
the segmentation genes.
 When a homeotic gene is mutated, the address is wrong and cells in the segment
develop as though they were somewhere else in the embryo.
 Homeotic genes in Drosophila are expressed after fertilization and are activated by
specific concentrations of the proteins produced by the gap, pair-rule, and
segmentpolarity genes. The homeotic gene Ultrabithorax (Ubx),
 for example, is activated when the concentration of Hunchback protein (a product
of a gap gene) is within certain values. These concentrations exist only in the
middle region of the embryo; so Ubx is expressed only in these segments.

23.  The homeotic genes in animals encode regulatory proteins that bind to DNA; each
gene contains a subset of nucleotides, called a homeobox, that are similar in all
homeotic genes.
 The homeobox encodes 60 amino acids that serve as a DNA-binding domain; this
domain is related to the helix-turn-helix motif Homeoboxes are also present in
segmentation genes and other genes that play a role in spatial development.
 There are two major clusters of homeotic genes in Drosophila. One cluster, the
Antennapedia complex, affects the development of the adult fly’s head and anterior
thoracic segments.
 The other cluster consists of the bithorax complex and includes genes that influence
the adult fly’s posterior thoracic and abdominal segments.
 Together, the bithorax and Antennapedia genes are termed the homeotic complex
(HOM-C).
 In Drosophila, the bithorax complex comprises three genes, and the Antennapedia
complex has five; all are located on the same chromosome
 In addition to these eight genes, HOM-C contains many sequences that regulate the
homeotic genes. Remarkably, the order of the genes in the HOM-C is the same as
the order in which the genes are expressed along the anterior–posterior axis of the
body.
 The genes that are expressed in the more-anterior segments are found at one end
of the complex, whereas those expressed in the more-posterior end of the embryo
are found at the other end of the complex.

27. Genetic mutations in
drosophila
 Drosophila genes are traditionally named after
the phenotype they cause when mutated. For example,
the absence of a particular gene in Drosophila will result
in a mutant embryo that does not develop a heart. [This
system of nomenclature results in a wider range of
gene names than in other organisms.
 bw: brown- The brown eye mutation results from
pteridine (red) pigments inability to be produced or
synthesized, due to a point mutation on chromosome
II. When the mutation is homozygous, the pteridine
pigments are unable to be synthesized because in the
beginning of the pteridine pathway, a defective enzyme
is being coded by homozygous recessive genes . In all,
mutations in the pteridine pathway produces a darker
eye color, hence the resulting color of the biochemical
defect in the pteridine pathway being brown.

28.  vg: vestigial- A spontaneous mutation, discovered in
1919 by Thomas Morgan and Calvin Bridges. Vestigial
wings are those not fully developed and that have lost
function. Since the discovery of the vestigial gene
in Drosophila melanogaster
 The vestigial gene is considered to be one of the most
important genes for wing formation, but when it
becomes over expressed the issue of ectopic wings begin
to form.
 The vestigial gene acts to regulate the expression of the
wing imaginal discs in the embryo and acts with other
genes to regulate the development of the wings.
 A mutated vestigial allele removes an essential sequence
of the DNA required for correct development of the
wings.

29. Drosophila in genetic analysis
 Useful characters of drosophila in
genetic analysis
 61% human diseases have recognizable
correspondence in genetic code of fruit
fly.
 50% of protein sequences have analogs
with analogs.
 The life cycle is relatively short and each
fly can produce number of progeny.
 Balancer chromosomes help preserve
linkage.

30.  Genetics A Conceptual Approach FOURTH
EDITION Benjamin A. Pierce
 w.w.w wikipedia.com
 www.slideshare.net

31. Thank you