Vulval development in the model organism Caenorhabditis elegans beautifully illustrates how cell signaling and fate decisions direct organogenesis. Two key players—the anchor cell and vulval precursor cells (VPCs)—coordinate via signaling molecules like LIN-3 and cellular interactions, producing a patterned vulva. Key mechanisms include equivalence groups, signaling gradients, and lateral inhibition that restrict and specify cell fates.

Explanation of the Statements About Vulval Development

A. Anchor cell is a germ cell from the gonad, which sends induction signal to vulva for maintaining differentiation states.

• Incorrect: The anchor cell is a somatic gonadal cell, not a germ cell. It acts as an inducer by secreting LIN-3 (an EGF-like protein), initiating vulval development and cell fate specification in VPCs.

B. The six vulval precursor cells, influenced by anchor cell, form an equivalence group.

• Correct: The six epidermal VPCs (P3.p through P8.p) initially have equivalent potential to form vulval tissue. The graded LIN-3 signal from the anchor cell assigns distinct fates to individual cells based on position and signaling intensity.

C. The cell directly beneath the anchor cell divides to form the central vulval cells, while the two flanking cells divide to become the lateral vulval cells.

• Correct: The central VPC (P6.p) adopts the primary (1°) vulval fate, dividing to form central vulval cells. Its immediate neighbors (P5.p and P7.p) adopt secondary (2°) fate, becoming lateral vulval cells.

D. The three cells further away from anchor cell generate hypodermal cells.

• Correct: The distal VPCs (P3.p, P4.p, and P8.p) do not participate in vulval formation under normal conditions but instead differentiate into hypodermal (skin) cells.

E. Lin3 signal from anchor cell forms a gradient and activates vulva forming genes in central and lateral cells.

• Correct: LIN-3 secretion creates an EGF gradient, with highest levels near P6.p, inducing 1° fate, lower levels at adjacent VPCs inducing 2° fate, and no activation farther away, leading to 3° fate.

F. The Notch-Delta mediated mechanism of restricting adjacent cell fates is called Lateral inhibition.

• Correct: Notch (LIN-12) signaling mediates lateral inhibition to restrict neighboring cells from adopting the same vulval fate, orchestrating the pattern of 1° and 2° fates in nearby VPCs.

Correct Combination of Statements

Given the above clarifications:

• Statement A is incorrect due to the anchor cell being somatic, not germline.

• Statements B, C, D, E, and F accurately describe vulval development roles and signaling mechanisms.

Therefore, the correct choice is:
(4) B, C, D, E and F

Developmental Significance

The interplay between the anchor cell’s LIN-3 signal and the competence of the VPC equivalence group generates a finely tuned pattern of vulval cells. Lateral inhibition via Notch signaling further refines this pattern by preventing neighboring cells from adopting identical fates, ensuring structural and functional diversity within the vulva. These processes exemplify fundamental developmental principles such as morphogen gradients, cellular competence, and selective cell communication.

Conclusion

The C. elegans vulva formation is orchestrated through the coordinated action of an equivalence group of vulval precursor cells, induction by the anchor cell’s LIN-3 gradient, and lateral inhibition mediated by Notch-Delta signaling. Among the proposed statements, the combination B, C, D, E, and F most accurately captures the complex biological realities governing this developmental system.