In regenerating limbs of amphibians such as newts, blastema cells at the amputation site harbor positional information that guides the regeneration of the correct limb parts. Retinoic acid (RA), a vitamin A derivative, plays a key role in modulating this positional information during regeneration, enabling altered patterning outcomes based on its concentration.

How Retinoic Acid Affects Positional Information in Blastema Cells

• RA Respecifies Blastema Cells to a More Proximal Positional Identity:
  When newt blastema cells are exposed to retinoic acid, their intrinsic positional values adjust such that they adopt characteristics of more proximal limb regions than their original position. This effect reprograms the blastema, often resulting in the regeneration of more proximal limb segments than might otherwise occur.

• Concentration-Dependent Effect:
  The degree of proximal respecification correlates with the level of RA exposure, highlighting its role as a morphogen that imparts graded positional information along the proximodistal axis during regeneration.

• Molecular Mechanisms:
  RA signaling upregulates proximal patterning genes such as Meis1 and Meis2, while downregulating distal limb patterning genes like Hoxa13, modulating gene expression to reflect proximal characteristics.

• Functional Significance:
  This re-specification ensures that regenerating limbs replace the correct skeletal segments, restoring proper limb anatomy even after varying levels of amputation.

Why Other Options Are Incorrect

• RA does not have no effect (eliminating option 1).

• RA does not make cells more distal in identity (eliminating option 3).

• RA does not cause loss of positional information with cells remaining undifferentiated (eliminating option 4).

Summary

Retinoic acid treatment during newt limb regeneration causes blastema cells at the amputation site to become re-specified to a more proximal position, ensuring proper regeneration of proximal skeletal structures. This role is essential for pattern integrity and is mediated through transcriptional regulation of positional genes.

The correct answer is:
(2) The cells will become re-specified to more proximal position.