The wingless (wg) gene, encoding a key segment polarity protein in Drosophila melanogaster, is crucial for defining and maintaining the boundaries of each developing segment. RNA interference (RNAi) targeting wingless expression in cells at the onset of its natural expression has significant developmental consequences.

Wingless Function and RNAi Impact

Wingless encodes a secreted signaling protein with a relatively short-range gradient that influences neighboring cells’ fate, including triggering engrailed expression in adjacent compartments. If wingless RNAi is expressed in wingless-expressing cells from the time this gene initiates expression, it results in a marked loss or reduction of wingless protein production.

Effects on Engrailed Expression and Segment Compartments

Given that wingless protein is necessary to maintain engrailed expression in adjacent cells, silencing wingless via RNAi would reduce or eliminate this signaling. This leads to reduced engrailed expression areas and disrupts the boundaries between the anterior and posterior compartments within segments. The posterior compartment, characterized by engrailed expression, is particularly affected, showing developmental abnormalities.

Evaluating the Provided Statements

• Statement A: Incorrect. RNAi against wingless reduces its expression rather than enhancing it; thus, the engrailed expression area would not broaden.

• Statement B: Incorrect. Wingless does not form a long-range gradient; its signaling is short-range and critical within the same segment.

• Statement C: Correct. The posterior compartment of each future segment, defined by engrailed expression, is affected due to loss of wingless-mediated signal.

• Statement D: Incorrect. Although engrailed expression initiates by pair-rule genes, its maintenance depends on wingless signaling, so posterior compartments are affected.

Correct Answer

The option that best represents the consequences of expressing wingless RNAi in wingless-expressing embryonic cells is:

(2) Only C

Conclusion

Expressing wingless RNAi during early Drosophila embryonic development disrupts the crucial wingless signaling required for maintaining engrailed expression and proper posterior compartment formation. This disruption impairs segmental patterning, specifically affecting the posterior compartment of each segment while showing no enhancement or broadening of engrailed expression. Understanding these dynamics highlights the tight regulation and short-range action of wingless in segment development.