35. Instructive and permissive interactions are two major modes of inductive interaction during development. The following compares some properties of cell lines and cord blood stem cells. Cell lines which are stored in liquid nitrogen, can be retrieved for experiments, where they behave as per their original self. Cord blood can also be retrieved from liquid nitrogen for procuring stem cells. Unlike cell lines, the stem cells can be additionally induced to undergo differentiation into desired lineage, which are very different from their original self.
The behaviour of cell lines and stem cells is analogous to which of the interactions?
(1) Both cell lines and stem cells show instructive interaction
(2) Cell lines show instructive interaction whereas stem cells show permissive interaction
(3) Cell lines show permissive interaction whereas stem cells show instructive interaction
(4) Both types of cells show permissive instruction

In developmental biology, inductive interactions between cells are categorized into two primary modes: instructive and permissive interactions. These modes describe how cells influence each other’s fate during embryogenesis or tissue differentiation, each characterized by distinctive mechanisms of action.

Instructive interactions occur when an inducing cell or tissue transmits specific signals that direct a responder cell to adopt a particular developmental pathway. This mode requires the receiving cell to interpret external information actively that leads to a change in its fate. For example, in the classical lens induction during eye development, the optic vesicle provides essential instructive signals to the overlying ectoderm to form the lens. Without this signal, the lens does not develop. Thus, instructive interactions instruct the responder cells on what to become.

Permissive interactions, in contrast, involve situations where the responding cell is already committed or specified to a particular fate, but environmental factors provide a supportive condition allowing this fate to be realized. The inducing signals here do not dictate cell fate but permit or enable the committed progenitor cells to progress along their predetermined pathways.

This distinction is well illustrated by comparing cell lines and stem cells preserved in liquid nitrogen:

• Cell lines, when thawed and cultured, maintain their original committed identity and function autonomously, analogous to permissive interactions where their fate is fixed and simply permitted to manifest by the environment.

• Stem cells from cord blood, however, can be coaxed or induced under the right conditions to differentiate into a variety of lineages, some vastly different from their original state. This capacity reflects instructive interactions, where external cues direct stem cell fate decisions actively.

Therefore, cell lines exhibit behavior similar to permissive interactions, while stem cells demonstrate instructive interactions when exposed to differentiation signals.

Hence, the accurate analogy in this context is:

(3) Cell lines show permissive interaction whereas stem cells show instructive interaction

Recognizing this distinction not only clarifies fundamental developmental processes but also informs approaches in regenerative medicine and cell-based therapies, where controlling stem cell fate through instructive cues is key to therapeutic success.

Answer: (3) Cell lines show permissive interaction whereas stem cells show instructive interaction