Final answer:
Calcium is the correct second messenger in the T-cell signaling pathway for the activation of NFAT. It plays a crucial role in the signaling cascade following T-cell receptor engagement, leading to the dephosphorylation and activation of NFAT. The correct answer is option 3.
Step-by-step explanation:
The student question asks which molecule is a second messenger in the T-cell signaling pathway that leads to the activation of NFAT (nuclear factor of activated T-cells). The list provided includes MAPK, NF-κB, Calcium, Fos, and Ras. Of these, Calcium is the second messenger that plays a pivotal role in the signaling pathway for T-cell activation.
Upon T-cell receptor engagement, a series of signal transduction events leads to the activation of phospholipase C (PLC), which subsequently produces inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 then binds to IP3 receptors on the endoplasmic reticulum, causing the release of sequestered Calcium ions into the cytoplasm. The increase in intracellular Calcium concentration is essential for the activation of calcineurin, a phosphatase that dephosphorylates NFAT, thereby allowing it to translocate to the nucleus and modulate gene expression.
In summary, Calcium is the correct option as the second messenger involved in T-cell signaling for NFAT activation. Other options such as MAPK, NF-κB, Fos, and Ras play different roles in various signaling pathways but are not considered second messengers in the context of this specific pathway.