Question

Which of the following statements about development is incorrect? a. As microtubules lengthen and slide apart, the shape of cells within the ectoderm changes. b. The extracellular matrix molecule fibronectin guides the movement of cells during development. c. The furrow formed during mitosis of cells in the developing embryo is centrally located to ensure all cells divide symmetrically. d. Cell surface cadherins regulate the ability of developing cells to adhere to one another. e. Integrins are responsible for transmitting information from the extracellular matrix to the cytoskeleton.

Short answer

The incorrect statement is: 'The furrow formed during mitosis of cells in the developing embryo is centrally located to ensure all cells divide symmetrically'.

Step-by-step solution

Understanding the role of microtubules

Microtubules do play a fundamental role in cell shape changes during development, especially in the ectoderm. Thus, the statement a. is correct.

Understand the function of extracellular matrix and fibronectin

The extracellular matrix molecule fibronectin does guide the movement of cells during development. Hence, the statement b. is also correct.

Understand the mitosis process and furrow formation

Mitosis is the process where a single cell divides into two cells. However, all dividing cells do not necessarily undergo symmetric division, and the furrow is not centrally placed in all instances. Therefore, the statement c. is incorrect.

Understand the role of cadherins

Cell surface cadherins do regulate the ability of developing cells to adhere to one another. Therefore, the statement d. is correct.

Understand the function of integrins

Integrins do play a crucial role in signaling between the extracellular matrix and the cytoskeleton, hence the statement e. is correct.

Key concepts

Cell Shape Changes

During development, cells undergo various shape changes that are crucial for forming different tissues and organs. One of the core components that influence these changes are microtubules. Microtubules are part of the cell's cytoskeleton and provide structural support.

When microtubules lengthen and slide apart, they effectively change the cell's shape by altering its internal structure, much like rearranging beams in a building might change its outline.

• These microtubules can polarize the cell, which is essential during early development, for example in the nervous system where long projections need to form.
• In the ectoderm, microtubule-driven shape changes can lead to the development of neural structures through processes like neurulation.

Understanding these transformations is key to comprehending how multicellular organisms develop complex body plans from simpler embryonic stages.

Extracellular Matrix Role

The extracellular matrix (ECM) is a network of proteins and polysaccharides outside cells that provides structural and biochemical support. One of its key components is fibronectin, which has significant roles in guiding cell movements during developmental processes.

Fibronectin acts as a track along which cells can migrate. It's like having a railway system that directs trains to their destinations:

• It interacts with cell surface receptors called integrins, which allows cells to "grip" onto the matrix and move. This is essential during tissue formation when cells need to arrive at precise locations.
• This process also allows cells to assemble into organized structures rather than forming an unorganized mass.

The guidance provided by fibronectin within the ECM plays a vital role in ensuring that cells reach their correct positions during development.

Cell Division Symmetry

Cell division symmetry refers to how a cell divides into two daughter cells. This process can occur symmetrically, leading to two identical cells, or asymmetrically, producing cells with different sizes or components.

During early embryonic development, not all divisions are symmetric:

• Symmetric division tends to occur in stem cells, helping maintain their population.
• Asymmetric division, however, is crucial for differentiation and morphogenesis, where cells start to take on different roles and characteristics.

Contrary to some beliefs, the furrow formed during mitosis isn’t always centrally located, and understanding where and how it forms is essential for grasping development intricacies.

Cell Adhesion

Cell adhesion is a vital process where cells interact and attach to neighboring cells through specialized molecules on their surfaces. Cadherins are key molecules in this process.

They function like glue, helping cells to stick together:

• Cadherins are calcium-dependent adhesion molecules that bind cells together within tissues.
• They play a significant role during development by maintaining structural integrity and transmitting signals that regulate cell differentiation and movement.

Cadherin-mediated adhesion not only maintains the form and function of tissues but also influences the cells’ fate during development, shaping everything from neural connections to tissue layers.

Signaling Pathways in Cells

Signaling pathways are communication networks that govern cellular processes like growth, differentiation, and response to environmental stimuli. During development, these pathways are vital for making sure cells behave correctly in their environment.

Key features of signaling pathways include:

• They often start at the cell surface where signals like growth factors or hormones trigger a series of events inside the cell.
• Pathways often involve a cascade of protein interactions, exaggerating signals to ensure the cell's proper response.
• One common pathway involves integrins, which help transmit signals from the extracellular matrix to guide cellular behavior.

Understanding these pathways is crucial for recognizing how cells change roles and form organized structures during development. Errors in these signaling processes can lead to developmental disorders or diseases.