Question

As seen in the figure at the right, if animal cap ectoderm of late stage frog blastulas (pregastrula) is removed, it will develop into epidermis. However, later in gastrulation if it is removed, it will become neural tissue. Give a hypothesis for a) what tissue represents an inducer in this b) what tissue might represent the responder c) How might you test this hypothesis? Compare and give an example of regional specification of induction and genetic specification of induction Compare, contrast, and give an example of the following types of a) paracrine signaling and b) juxtacrine signaling and c) autocrine signaling

Answer 1

ectodermal cells acts as inducer.

neural tissue is responder.

Paracrine signaling is a form of cell-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behavior or differentiation of those cells. Signaling molecules known as paracrine factors diffuse over a relatively short distance (local action).

Growth factor and clotting factors are paracrine signaling agents. Also, retinoic acid, the active form of vitamin A, functions in a paracrine fashion to regulate gene expression during embryonic development in higher animals.In insects, Allatostatin controls growth though paracrine action on the corpora allata.

In mature organisms, paracrine signaling is involved in responses to allergens, tissue repair, the formation of scar tissue, and blood clotting.

Juxtacrine signalling (or contact-dependent signalling) is a type of cell / cell or cell / extracellular matrix signalling in multicellular organisms that requires close contact.

Three types of Juxtacrine signalling-

1. A membrane ligand (protein, oligosaccharide, lipid) and a membrane protein of two adjacent cells interact.
2. A communicating junction links the intracellular compartments of two adjacent cells, allowing transit of relatively small molecules.
3. An extracellular matrix glycoprotein and a membrane protein interact.   

Examples-in unicellular organisms such as bacteria, juxtacrine signaling refers to interactions by membrane contact

For some growth factors, cytokine and chemokine cellular signals, playing an important role in the immune response. It has a critical role in development, particularly of cardiac and neural function.

Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell.This can be contrasted with paracrine signaling and juxtacrine signalling.

An example of an autocrine agent is the cytokine interleukin-1 in monocytes. When interleukin-1 is produced in response to external stimuli, it can bind to cell-surfacereceptors on the same cell that produced it.

Another example occurs in activated T cell lymphocytes.Autocrine signaling plays critical roles in cancer activation and also in providing self-sustaining growth signals to tumors.