Morphogenesis and organogenesis in animals MCQ Quiz in मराठी - Objective Question with Answer for Morphogenesis and organogenesis in animals - मोफत PDF डाउनलोड करा

The correct answer is Option 4 i.e.Specification of the digit is primarily dependent on the amount of time the Shh gene is expressed and to a small extent on the concentration of the Shh protein that other cells receive.

Key Points

• A signaling molecule known as Sonic Hedgehog (Shh) is essential for the growth of extremities.
• The zone of polarizing activity (ZPA), which is found in the back of the growing limb opening, secretes Shh.
• During limb development, Shh signaling plays a role in defining the anterior-posterior axis.
• Additionally, its downstream signaling networks support cell proliferation, differentiation, and survival.
• Shh signaling is crucial for defining the back of the growing limb, including the development of the fingers.
• Other signaling molecules such as FGF, BMP, and Wnt control Shh expression during limb growth.
• Higher amounts of Shh expression are found in the back of the limb bud thanks to the assistance of these molecules.

Explanation:

Option 1 - INCORRECT

• Shh-secreting cells do not undergo apoptosis after performing their function.
• Shh plays a vital role in specifying the anterior-posterior axis during limb development, and its downstream signaling pathways are involved in several processes, including cell proliferation, differentiation, and survival.

Option 2 - INCORRECT

• Shh signaling is involved in specifying the posterior part of the developing limb, and its downstream signaling pathways contribute to the formation of bone and muscle.
• The descendants of Shh-secreting cells give rise to the posterior part of the limb, while the anterior part is specified by other signaling molecules.

Option 3 - INCORRECT

• Shh plays a crucial role in specifying digit formation during limb development, and knockout studies have shown that loss of Shh and its downstream effector Gli3 results in limb abnormalities but not in absence of digits.

Option 4 - CORRECT

• The duration of Shh gene expression is a primary determinant of digit specification during limb development.
• The concentration of Shh protein that other cells receive also influences digit formation, but to a lesser extent than the duration of Shh gene expression.

Therefore, the correct answer is Option 4.

Concept:

• Dorsoventral polarity in the egg chamber of Drosophila involves the localization of maternal gurken RNA to the dorsal side of the oocyte.
• The gurken protein has homology to secreted growth factors and may bind to the torpedo/DER receptor tyrosine kinase present on the adjacent follicle cells.
• This localized signal from the oocyte to the follicle cells appears to initiate a cascade of events leading to dorsal follicle cell differentiation, and delimiting and orienting the future dorsoventral axis of the embryo.

​

Explanation:

Fig 1: Steps involved in Dorso-ventral patterning of Drosophila embryo

• The nucleus of the oocyte travels to what will become the dorsal side of the embryo.
• The gurken genes of the oocyte synthesize mRNA that becomes localized between the oocyte nucleus and the cell membrane, where it is translated into Gurken protein.
• The Gurken signal is received by the Torpedo receptor protein made by the follicle cells .
•  Given the short diffusibility of the signal, only the follicle cells closest to the oocyte nucleus (i.e., the dorsal follicle cells) receive the Gurken signal, which causes the follicle cells to take on a characteristic dorsal follicle morphology and inhibits the synthesis of Pipe protein.
• Therefore, Pipe protein is made only by the ventral follicle cells.
•  The ventral region, at a slightly later stage of development.
• Sulfated proteins on the ventral region of the vitelline envelope recruit Gastrulation-defective (GD), which in turn complexes with other proteins, initiating a cascade that results in the cleaved Spätzle protein binding to the Toll receptor.
• The resulting cascade ventralizes the cell.

 hence the correct answer is option 1

The correct answer is Option 4 i.e. A and C

Key Points

• The third axis of limb development (dorsal-ventral) is the distinguishment of the dorsal limb from the ventral limb.
• Ectoderm determines the dorsal-ventral polarity of the limb bud.
• Wnt7a is the protein that is expressed in the ectoderm and plays a critical role in determining the dorsal-ventral axis of the limb bud.
• Mutation in the Wnt7a gene leads to the development of sole on both sides of the mouse paw, which leads to the conclusion that Wnt7a is needed for the dorsal patterning of the limb.
• Wnt7a activates the Lmx1b gene in the dorsal mesenchyme and Lmx 1b codes for a transcription factor that is required for dorsal cell fats on the limb.
• Loss of function of Lmx 1b gene, leads to loss of dorsal limb phenotype. 

Explanation:

• Lmx1b gene is expressed in the dorsal mesenchyme and it is required for determining dorsal limb fat. Mutation in the Lmx 1b gene in humans leads to Nail-patella syndrome. 
• Lmx1b gene expression is induced by the Wnt7a, an activator expressed in the ectoderm. 
• So, genes Lmx1b and Wnt7a are associated with nail-patella syndrome.

Hence, the correct answer is Option 4.

Additional Information

• Hoxa13 and Hoxd13 are responsible for determining the proximal and distal axis of the limb.
• Shh is responsible for determining the anterior-posterior axis of the limb.
• Tbx5 is a transcription factor that is expressed in the forelimb. It directly activates the Fgf10 gene via a conserved binding site, thereby providing a simple and direct mechanism for limb bud initiation.

The correct answer is Defective eye development

Explanation:

Sonic hedgehog (Shh) signaling is crucial in various developmental processes, including the establishment of left-right asymmetry, cell differentiation, and organogenesis. In zebrafish, inhibition of Shh can lead to significant developmental defects.​

Reduced Limb Bud Formation

• Shh is crucial for limb bud development and patterning in many vertebrates (such as mammals).
• However, zebrafish lack true limb buds in the way that tetrapods (like mice and humans) have them. Instead, zebrafish develop pectoral fins, and although Shh is involved in fin patterning, the effect of inhibiting Shh on limb formation in zebrafish would not be as pronounced as it is in tetrapods. Therefore, reduced limb bud formation is less relevant in zebrafish than in organisms that develop limbs.

Defective Eye Development

• Shh is critical in eye field separation during early embryonic development. Inhibition of Shh can lead to failure of eye field division, resulting in defects like cyclopia (a single central eye) or incomplete eye formation.
• This effect is particularly well-documented in zebrafish, as Shh signaling regulates midline structures that are essential for proper eye separation and formation. Therefore, defective eye development is a well-established consequence of Shh inhibition in zebrafish, making it the correct answer.

Failure in Neural Tube Closure

• Shh is crucial for ventral neural tube patterning, but neural tube closure defects are not typically observed in zebrafish because zebrafish do not have a neural tube that closes in the same way as mammals do.
• In mammals, the neural tube forms by a folding process that closes along the dorsal side, and Shh is vital in the patterning and closure of this structure.
• However, in zebrafish, the neural tube forms through a different process called secondary neurulation, where cells organize into a solid neural keel and later form a neural tube, so Shh inhibition would not lead to a failure of neural tube closure in the way it would in mammals.

Loss of Left-Right Asymmetry

• Shh signaling does play a role in establishing left-right asymmetry in many vertebrates, and its inhibition could disrupt the asymmetric development of organs. However, the left-right asymmetry in zebrafish is less directly dependent on Shh signaling compared to other signals (such as Nodal signaling).
• While Shh has some involvement, defects in left-right asymmetry due to Shh inhibition are not as prominent or consistent in zebrafish as defects in eye development are. This effect is secondary and less specific than its role in eye development..

The correct answer is Option 4

Explanation:

• In C. elegans vulva induction, the LIN-3 ligand plays a pivotal role as the primary initiator of the signaling pathway that leads to vulval development.
• Produced by the anchor cell in the gonad, LIN-3 acts as a ligand for the EGF receptor LET-23, which is located on the surface of the vulval precursor cells (VPCs).
• Binding of LIN-3 to LET-23 activates the receptor, initiating a cascade of intracellular signaling events.
• This signaling cascade involves several key proteins, including the LET-60 Ras and LIN-45 Raf, and ultimately leads to the differentiation of the VPCs into the vulval structure.
• The specificity of the LIN-3/LET-23 interaction and the subsequent signaling pathway is crucial for the precise development of the vulva, showcasing an elegant example of how intercellular communication and signaling pathways orchestrate complex developmental processes in organisms.

Conclusion:

Therefore, the correct statement is "LIN-3, produced by the gonad, binds to the EGF receptor LET-23 on VPCs, initiating a signaling cascade essential for vulval development"

The correct answer is Option 2 i.e.A, B, D and E only 

Explanation-

The experiment involving the removal and replacement of the Apical Ectodermal Ridge (AER) during chick wing development provides insights into the interactions between the AER and limb mesenchyme. The statements are as follows:

A. The limb mesenchyme cells induce and sustain AER:

• The removal of AER leads to the cessation of limb development. This indicates that AER is crucial for sustaining limb development. Therefore, the mesenchyme cells beneath the AER induce and sustain AER, promoting limb growth.

B. The mesenchyme cells specify the type: wing or limb:

• Placing leg mesenchyme beneath the wing AER results in the development of distal hindlimb structures at the end of the wing. This implies that the type of limb (wing or limb) is specified by the characteristics of the mesenchyme cells.

C. The AER is responsible for specifying the type: wing or limb:

• The replacement of limb mesenchyme with non-limb mesenchyme beneath the AER results in AER regression. This suggests that the AER is sensitive to the type of mesenchyme and regresses when non-limb mesenchyme is present.

D. The AER is responsible for sustained outgrowth and development of the limb:

• The AER is crucial for the sustained outgrowth and development of the limb, as demonstrated by the cessation of limb development upon AER removal.

E. The AER does not specify the type: wing or limb:

• The AER's role is in sustaining limb outgrowth, but the specific type of limb is determined by the characteristics of the underlying mesenchyme.

Conclusion:The experiment demonstrates that the mesenchyme cells play a role in inducing and sustaining the AER, specifying the limb type. The AER, in turn, is responsible for the sustained outgrowth and development of the limb. The specific type of limb is influenced by the characteristics of the underlying mesenchyme. The correct combination of statements is 2) A, B, D, and E only.

 Key PointsThe apical ectodermal ridge is a multipurpose signaling center that will influence patterning along all axes of limb development. The diverse roles of the AER include

(1) maintaining the mesenchyme beneath it in a plastic, proliferating state that enables the linear (proximal-distal, or shoulder finger) growth of the limb;

(2) maintaining the expression of those molecules that generate the anterior-posterior  (thumb-pinkie) axis; and

(3) interacting with the proteins specifying the anterior-posterior and dorsal-ventral (knuckle-palm) axes so that each cell is given instructions on how to differentiate 
The proximal-distal growth and differentiation of the limb bud are made possible by a series of interactions between the AER and the limb bud mesenchyme directly (200 µm) beneath it. This mesenchyme is called the progress zone (PZ) mesenchyme because its proliferation extends the limb bud. These interactions were demonstrated by the results of several experiments on chick embryos:

• If the AER is removed at any time during limb development, further development of distal limb skeletal elements ceases.
• If an extra AER is grafted onto an existing limb bud, supernumerary structures are formed, usually toward  the distal end of the limb.
• If leg mesenchyme is placed directly beneath the wing AER, distal hindlimb structures (toes) develop at the end of the limb. (If this mesenchyme is placed farther from the AER, however, the hindlimb [leg] mesenchyme becomes integrated into wing structures.)
• If limb mesenchyme is replaced by nonlimb mesenchyme beneath the AER, the AER regresses and limb development ceases.

Fig-Manipulation of the apical ectodermal ridge (AER)

The correct answer is Option 1 i.e. A only.

Explanation-

A. The regenerating blastema cells in amphibians retain their specification even when they dedifferentiate:

• In blastema-mediated regeneration, differentiated cells undergo dedifferentiation to form undifferentiated cells. These cells then start proliferating to form a mass of heterogeneous undifferentiated cells at the regenerating tip called blastema. Once a necessary number of cells are amassed, the cells in blastema start to redifferentiate and initiate the process of morphogenesis similar to that seen during embryogenesis. This process then culminates with the restoration of the lost tissue, either completely or partially depending upon the organism.
• In compensatory regeneration, the regeneration proceeds without any blastema formation or requirement of stem cells. In this process, differentiated cells from the vicinity are recruited to the site of injury and proliferate to replace the lost tissue. Liver regeneration is a prime example of compensatory regeneration.

B. A transgenic Hydra when made to misexpress β-catenin will show numerous ectopic tentacles:

• This statement is incorrect. In Hydra, misexpression of β-catenin does not lead to the formation of ectopic tentacles.

C. In Planaria, if the Wnt pathway is activated, then the posterior blastema would regenerate a head:

• This statement is incorrect. In Planaria, activation of the Wnt pathway in the posterior blastema promotes tail regeneration, not head regeneration.

D. A regenerating blastema is formed in the mammalian liver:

• This statement is incorrect. While the liver has some regenerative capacity, it does not typically involve the formation of a blastema. The regeneration in the liver often occurs through the proliferation of existing hepatocytes.

Conclusion- So, the correct answer is Option 1 

The correct answer is Pair rule genes

Explanation:

• Segmentation genes in Drosophila, also known as the gap genes, pair-rule genes, and segment polarity genes, are a group of genes that play a crucial role in the development of body segments in the fruit fly Drosophila melanogaster.

These genes are involved in determining the spatial organization and identity of the segments along the anterior-posterior axis of the embryo.
Gap genes:

• Gap genes are the first class of segmentation genes to be expressed in the developing Drosophila embryo.
• They are responsible for dividing the embryo into broad regions or "gaps" along the anterior-posterior axis. Gap genes set up the initial broad pattern of segmentation by controlling the expression of pair-rule genes.
• Examples of gap genes include Krüppel (Kr), hunchback (hb), and knirps (kni). Mutations in gap genes lead to the loss or deletion of several adjacent segments.

Pair-rule genes:

• Pair-rule genes are expressed in alternating segments along the embryo, hence the name "pair-rule."
• They refine the initial broad pattern established by the gap genes and divide the embryo into individual segments.
• The expression of pair-rule genes is regulated by the gap genes.
• Examples of pair-rule genes include even-skipped (eve), hairy (h), and runt (run).
• Mutations in pair-rule genes result in the loss or deletion of specific segments, typically every other segment.

Segment polarity genes:

• Segment polarity genes determine the anterior-posterior polarity within each segment.
• They are expressed in a striped pattern within each segment and are responsible for establishing the identity of the individual segments.
• Examples of segment polarity genes include engrailed (en), wingless (wg), and hedgehog (hh).
• Mutations in segment polarity genes cause defects in the patterning of individual segments, such as mirror-image duplications or deletions within segments.

Table: Major genes affecting segmentation pattern in Drosophila

Conclusion: Therefore, fushi tarazu (ftz) belongs to pair rule genes.

The correct answer is Amphibians.

Explanation-

Amphibians do exhibit the phenomenon of "bottle cells" during gastrulation, which is a crucial stage of early embryonic development. This is particularly observed in amphibians such as frogs and sea urchins.

• Bottle cells are specialized epithelial cells that undergo a shape change during the beginning of gastrulation. These cells are called 'bottle cells' because of their unique appearance - the cells have a wide apical end (the top of the cell) and a narrow basal end (the bottom of the cell), hence their shape is reminiscent of a bottle.
• These cells play a major role in the initiation of gastrulation, by helping to create the blastopore, an opening into the embryo through which cells move from the exterior to the interior during gastrulation.
• When these cells change shape, it causes a bending of the tissue, a process known as invagination, which results in the formation of a depression on the surface of the embryo that eventually becomes the blastopore.

Fig- Early movements of Xenopus gastrulation.

Concept:

• Dorsoventral polarity in the egg chamber of Drosophila involves the localization of maternal gurken RNA to the dorsal side of the oocyte.
• The gurken protein has homology to secreted growth factors and may bind to the torpedo/DER receptor tyrosine kinase present on the adjacent follicle cells.
• This localized signal from the oocyte to the follicle cells appears to initiate a cascade of events leading to dorsal follicle cell differentiation, and delimiting and orienting the future dorsoventral axis of the embryo.​

Explanation:

Fig 1: Steps involved in Dorso-ventral patterning of Drosophila embryo

The nucleus of the oocyte travels to what will become the dorsal side of the embryo.

• The gurken genes of the oocyte synthesize mRNA that becomes localized between the oocyte nucleus and the cell membrane, where it is translated into Gurken protein.
• The Gurken signal is received by the Torpedo receptor protein made by the follicle cells .
•  Given the short diffusibility of the signal, only the follicle cells closest to the oocyte nucleus (i.e., the dorsal follicle cells) receive the Gurken signal, which causes the follicle cells to take on a characteristic dorsal follicle morphology and inhibits the synthesis of Pipe protein.
• Therefore, Pipe protein is made only by the ventral follicle cells.
•  The ventral region, at a slightly later stage of development.
• Sulfated proteins on the ventral region of the vitelline envelope recruit Gastrulation-defective (GD), which in turn complexes with other proteins, initiating a cascade that results in the cleaved Spätzle protein binding to the Toll receptor.
• The resulting cascade ventralizes the cell.

​

 hence the correct answer is option 1