During vulva formation in Caenorhabditis elegans, six vulval precursor cells (VPCs) initially have the potential to contribute to the vulva structure. Classic experiments show that even if three of these six cells are ablated, a normal vulva can still form, showcasing remarkable developmental plasticity and robustness.

Key Reasons Explaining Vulva Formation Despite Ablation

A. Six hypodermal VPCs form an equivalence group of cells, with only three typically participating in vulva formation, while the others serve as reserve cells.

• This means all six cells are initially competent and equivalent in their ability to become vulval cells.

• Normally, the three closest VPCs to the anchor cell receive inducing signals and form the vulva.

• The remaining cells do not usually participate but retain the ability to do so if necessary.

B. When three hypodermal VPCs are killed, the three neighboring hypodermal non-VPCs get freshly recruited to compensate.

• The developmental system is flexible enough that if some VPCs are lost, adjacent competent cells can be recruited to take over the vulval fate.

• This recruitment preserves the developmental outcome despite cell loss.

Role of the Anchor Cell Induction

C. The anchor cell functions as an inducer, emitting signals (specifically LIN-3/EGF) that initiate vulval development.

• It induces the nearest VPCs to differentiate into vulval cells.

• However, its inductive range is spatially limited, and it does not recruit distant gonadal epithelial cells to replace lost VPCs.

D. Anchor cell spatially induces only three hypodermal cells.

• Normally, only the three VPCs closest to the anchor cell receive enough signal to become vulval.

• This suggests an induction gradient restricting vulval fate to a subset of VPCs.

Correct Combination of Statements

From the above explanations and scientific evidence:

• Statement A correctly describes the equivalence group concept with reserve cells.

• Statement B accurately reflects the recruitment of neighbor VPCs when some are killed.

• Statement C is only partially true: the anchor cell induces vulval fate but does not recruit gonadal epithelial cells beyond the VPC group.

• Statement D is correct about the spatial restriction of the signal.

Because only A and B align completely with the observed phenomenon that a normal vulva forms after three VPC ablations due to cellular equivalence and recruitment, the correct answer is:

(1) A and B