Download BSc in Applied Biotechnology 5 BO0053 ‑ DEVELOPMENTAL

PROGRAM
BSc in Applied Biotechnology
SEMESTER
5
SUBJECT
BO0053 - DEVELOPMENTAL BIOLOGY
BOOK ID
B0960
SESSION
Winter 2015
No
Q 1
Question/Answer key
Marks Total Marks
10
Explain the role of Bone Morphogenetic Proteins (BMP) in development.
( Unit 5 ; Section 5.4 )
A 1
Role of Bone Morphogenetic Proteins (BMP) in development.
Bone morphogenetic proteins (BMP) are involved in numerous developmental
interactions whereby one set of cells interacts with other neighboring cells to alter
their properties.
• The members of the BMP family were originally discovered by their ability to
induce bone formation therefore, they are the bone morphogenetic proteins.
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• They have been found to regulate cell division, apoptosis (programmed cell
death), cell migration, and differentiation.
• BMPs can be distinguished from other members of the TGF-β superfamily by
their having seven, rather than nine, conserved cysteines in the mature
polypeptide.
• The BMPs include proteins such as Nodal and BMP4.
• The Drosophila Decapentaplegic protein is homologous to the vertebrate
BMP4, and human BMP4 can replace the Drosophila homologue, rescuing those
flies deficient in Dpp.
• BMP-4 is secreted throughout the embryonic disc.
• In the presence of this protein and fibroblast growth factor (FGF), mesoderm
will be ventralized to contribute to kidneys, blood and body wall mesoderm.
• In fact, all mesoderm would be ventalized if the activity of BMP-4 were not
blocked by other genes expressed in the node like chordin, noggin, and follistatin.
• BMP7 has been implicated as a protein that prevents cell death and promotes
cell division in several developing organs.
• Noggin binds to BMP4 and BMP2 and inhibits their binding to receptors.
• Like Noggin, chordin binds directly to BMP4 and BMP2 and prevents their
complexing with their receptors.
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• When BMP binds to ectodermal cells, it activates the expression of genes such
as msx1, which induce the expression of epidermal-specific genes, while
inhibiting those genes that would produce a neural phenotype.
• In the mesoderm, BMP4 activates genes such as Xvent1, which give the
mesoderm a ventral phenotype.
• Low doses of BMP4 appear to activate muscle formation; intermediate levels
instruct cells to become kidney; and high doses activate those genes that instruct
the mesoderm to become blood cells.
• The varying doses are created by the interaction of BMP4 with the BMP
antagonists coming from the organizer.
• Thus BMP4 is the active inducer of ventral ectoderm and the ventralizer of the
mesoderm), and that Noggin, chordin, and follistatin could prevent its function.
• The organizer worked by secreting inhibitors of BMP4, not by directly inducing
neurons.
Q 2
10
Define gastrulation. Describe the process of gastrulation during embryonic
development.
( Unit 2 ; Section 2.7 )
A 2
Definition of gastrulation
Gastrulation is the process of highly coordinated cell and tissue movements
whereby the cells of the blastula are dramatically rearranged.
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The process of gastrulation
The three germ layers outer ectoderm, inner endoderm, and interstitial mesoderm
are first produced during gastrulation.
• Formation of the primitive streak, germ layers and notochord are the important
processes occurring during gastrulation.
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• During gastrulation, the embryo may be called a gastrula.
• Coeloblastulae often gastrulate by invagination.
• Cells near the vegetal pole grow inward leading to an archenteron and a
blastopore.
• The inner cells are endoderm and the outer cells are ectoderm.
• Some coeloblastulae undergo ingression in which cells near the vegetal pole
grow to fill the blastocoel.
• This leads to a solid gastrula called a stereogastrula.
• Rarely, cells of the blastula divide to form cells just below them in
delamination.
• Stereoblastulae that result from holoblastic cleavage generally undergo
epiboly.
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• Cells from the animal pole grow over the rest of the blastula.
• The archenteron occurs secondarily.
• Discoblastulae often gastrulate by involution. Cells around the disc proliferate
and grow under the disc. The yolk is still present.
• True mesoderm is derived from endoderm.
• If a middle layer is derived from ectoderm, it is ectomesoderm and the animal
is considered diploblastic.
• Schizocoely – In organisms with spiral cleavage, the 4d micromere proliferates
between the archenteron and the ectoderm to form a solid mass of mesoderm.
• Enterocoely - In other organisms endoderm pouches off the archenteron and
becomes mesoderm.
• A true coelom is completely surrounded by mesoderm.
• Some organisms have coeloms that are not surrounded by mesoderm. These
are called pseudocoelomates or blastocoelomates.
Q 3
10
Explain the various steps involved in the development of brain.
A 3
( Unit 3 ; Section 3.5 )
Steps involved in the development of brain.
The central nervous system (CNS) appears in the beginning as slipper like plate
of thickened ectoderm, the neural plate, in the middorsal region in front of the
primitive node.
• Its lateral edges soon elevate to form the neural folds With further
development, the neural folds continue to elevate, approach each other in the
midline, and finally fuse, forming the neural tube.
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• Fusion begins in the cervical region and proceeds in cephalic and caudal
directions.
• Once fusion is initiated, the open ends of the neural tube form the cranial and
caudal neuropores that communicate with the overlying amniotic cavity.
• Closure of the cranial neuropore proceeds cranially from the initial closure site
in the cervical region and from a site in the forebrain that forms later.
• This later site proceeds cranially, to close the rostralmost region of the neural
tube, and caudally to meet advancing closure from the cervical site.
• The cephalic end of the neural tube shows three dilations, the primary brain
vesicles:
(a) The prosencephalon, or forebrain;
(b) the mesencephalon, or midbrain; and
(c) The rhombencephalon, or hindbrain.
Simultaneously it forms two flexures: (a) the cervical flexure at the junction of the
hindbrain and the spinal cord and (b) the cephalic flexure in the midbrain region.
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• The prosencephalon consists of two parts:
(a) the telencephalon, formed by a midportion and two pocketings, the primitive
cerebral hemispheres, and
(b) The diencephalon, characterized by outgrowth of the optic vesicles.
• A deep furrow, the rhombencephalic isthmus, separates the mesencephalon
from the rhombencephalon.
• The rhombencephalon also consists of two parts:
(a) The metencephalon, which later forms the pons and the cerebellum, and
(b) The myelencephalon. The boundary between these two portions is marked by
the pontine flexure.
• The lumen of the spinal cord, the central canal, is continuous with that of the
brain vesicles.
• The cavity of the rhombencephalon is the fourth ventricle, that of the
diencephalon is the third ventricle, and those of the cerebral hemispheres are the
lateral ventricles.
• The lumen of the mesencephalon connects the third and fourth ventricles.
• This lumen becomes very narrow and is known as the aqueduct of Sylvius.
• The lateral ventricles communicate with the third ventricle through the
interventricular foramina of Monro.
Q 4
10
Describe the process of determining anterior posterior axis in Drosophila.
A 4
( Unit 4 ; Section 4.4 )
Process of determining anterior posterior axis in Drosophila.
The anterior-posterior and dorsal-ventral axes of Drosophila form at right angles
to one another, and they are both determined by the position of the oocyte within
the follicle cells of the ovary.
• The anterior-posterior polarity of the embryo, larva, and adult has its origin in
the anterior-posterior polarity of the egg.
10
• The maternal effect genes expressed in the mother's ovaries produce
messenger RNAs that are placed in different regions of the egg. These messages
encode transcriptional and translational regulatory proteins that diffuse through
the syncytial blastoderm and activate or repress the expression of certain zygotic
genes.
• Two of these proteins, Bicoid and Hunchback, regulate the production of
anterior structures, while another pair of maternally specified proteins, Nanos and
Caudal, regulates the formation of the posterior parts of the embryo.
• The zygotic genes regulated by these maternal factors are expressed in
certain broad (about three segments wide), partially overlapping domains. These
genes are called gap genes and they are among the first genes transcribed in the
embryo.
• Differing concentrations of the gap gene proteins cause the transcription of
pair-rule genes, which divide the embryo into periodic units.
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• The transcription of the different pair-rule genes results in a striped pattern of
seven vertical bands perpendicular to the anterior-posterior axis.
• The pair-rule gene proteins activate the transcription of the segment polarity
genes, whose mRNA and protein products divide the embryo into 14
segment-wide units, establishing the periodicity of the embryo.
• At the same time, the protein products of the gap, pairrule, and segment
polarity genes interact to regulate another class of genes, the homeotic selector
genes, whose transcription determines the developmental fate of each segment.
Q 5
10
Explain the Wnt signalling Pathway.
( Unit 5 ; Section 5.4 )
A 5
Wnt signalling Pathway
The Wnts constitute a family of cysteine rich glycoproteins.
• Wnt proteins are also critical in establishing the polarity of insect and
vertebrate limbs, and they are used in several steps of urogenital system
development.
10
• Members of the Wnt family of paracrine factors interact with transmembrane
receptors of the Frizzled family.
• In most instances, the binding of Wnt by the Frizzled protein causes the
Frizzled protein to activate the Disheveled protein.
• Once the Disheveled protein is activated, it inhibits the activity of the glycogen
synthase kinase-3 enzyme. GSK-3, if it were active, would prevent the
dissociation of the β-catenin protein from the APC protein, which targets
β-catenin for degradation.
• However, when the Wnt signal is given and GSK-3 is inhibited, β-catenin can
dissociate from the APC protein and enter the nucleus.
• Once inside the nucleus, it can form a heterodimer with an LEF or TCF
DNA-binding protein, becoming a transcription factor. This complex binds to and
activates the Wnt-responsive genes.
Q 6
10
Define apoptosis. Explain the process of apoptosis pathway in mammalian
neurons.
A 6
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( Unit 7 ; Section 7.3 )
Definition of apoptosis
Apoptosis is a genetically controlled cell death that causes cells to shrink and be
eliminated without the tissue traumas associated with inflammation that
accompanies uncontrolled cell death (necrosis).
2
The process of apoptosis pathway in mammalian neurons.
In apoptosis proteolytic enzymes (notably caspases – Cysteine ASpartase
ProteASES) begin the process of orderly protein degradation that culminates in
the production of small packages of cellular remnant.
• Apoptosis initiated by an extracellular signal (Fas receptor) activates
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caspase 8, whereas apoptosis due to intracellular damage or distress activates
caspase 9.
• Both caspase 8 and caspase 9 are initiator caspases, which can activate
caspase 3, the primary effector caspase, which induces apoptosis.
• The tumor-suppressor protein p53 can be a potent initiator of apoptosis,
whereas anti-apoptotic Bcl−2 is an oncogene because mutations in the gene
increase Bcl−2 protein expression, thereby protecting cancer cells from
apoptosis.
• If intracelluar Ca2+ is high, p53 may be bypassed because high mitochondrial
Ca2+ opens the Mitochondrial Permeability Transition Pore (MPTP) causing
energy uncoupling (reduced inner membrane proton gradient), increased
superoxide production, reduced ATP production and the release of cytochrome c
to the cytosol – which activates caspase 9.
• Caspase 9 activates caspase 3 and caspase 7 by forming an apoptosome with
cytochrome−c and Apoptotic Protease Activating Factor−1 (APAF−1). Oxidative
stress, DNA damage and cell stress other than high Ca2+ may induce Bid protein
to form Bax/Bak channels and release of cytochrome−c
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