Correct option is B
We are asked which combination of the following statements is correct regarding amphibian development.
Breakdown of Statements:
Statement A: "Fibronectin plays an important role in enabling the mesodermal cells to migrate into the embryo."
Correct: Fibronectin is indeed a crucial extracellular matrix protein that plays a major role during gastrulation in amphibians. It helps mesodermal cells migrate into the embryo, aiding in mesodermal cell movement and cell adhesion. This is a well-established concept in developmental biology.
Statement B: "Organizer secretes proteins that block the BMP signal, which allows the ectodermal cells to become epidermis."
Incorrect: The organizer (specifically the Spemann organizer) secretes proteins that block BMP signaling, but this BMP blockade allows the ectodermal cells to become neural tissue (neural induction), not epidermis. In the presence of BMP signaling, ectodermal cells will become epidermis. The role of the organizer is to induce neural tissue by blocking BMP, so this statement is incorrect.
Statement C: "Wnt signaling causes a gradient of β-catenin along the anterior-posterior axis of the neural plate, which appears to specify the regionalization of the neural tube."
Correct: Wnt signaling plays a crucial role in the specification of the anterior-posterior axis of the neural tube. A gradient of β-catenin in the neural plate helps in defining the regionalization of the neural tube. This mechanism is essential in specifying the development of different regions of the neural tube (such as the hindbrain and spinal cord), making this statement accurate.
Statement D: "The more ventral blastomeres in the endoderm have high expression of nodal-related proteins."
Incorrect: Nodal-related proteins are important for mesodermal and endodermal patterning, but the expression of nodal-related proteins is actually higher in the dorsal part of the embryo (not ventral) to specify the dorsal-ventral axis. This statement misrepresents the distribution of nodal-related proteins in the endoderm. The ventral side of the embryo is typically associated with other signaling pathways, not high nodal-related protein expression, making this statement incorrect.
Correct Combination:
Option 2 (A and C) is correct because both Statement A and Statement C accurately describe aspects of amphibian development:
Statement A is correct regarding the role of fibronectin in mesodermal migration.
Statement C is correct about the role of Wnt signaling and the β-catenin gradient in neural tube regionalization.
Information Booster:
Fibronectin in Mesodermal Migration: During gastrulation in amphibians, fibronectin provides a scaffold for mesodermal cells to adhere to and migrate into the embryo. This migration is a key part of the formation of the mesoderm and its subsequent differentiation into various tissues.
Wnt Signaling and β-Catenin: Wnt signaling is involved in many aspects of early development, including the specification of the anterior-posterior axis of the neural tube. The β-catenin gradient formed by Wnt signaling helps regionalize the neural plate, guiding the proper formation of structures along the anterior-posterior axis of the neural tube.
