Discussion:
Blue stain was
observed in the wing and leg imaginal discs of En-lacZ larva only. Therefore, it was suggested that the promoter lacZ was successfully incorporated into
the Drosophila genome.
The posteriorly localized staining
patterns observed in the En-lacZ larva
wing and leg discs match significantly with the known engrailed expression patterns (Gilbert, 2003). However, simply
observing the expression patterns of engrailed
is not helpful in determining the exact roles of engrailed. The literature notes that engrailed might be involved in the compartmentalization and
anterior-posterior patterning of the imaginal discs (Gilbert, 2003).
Verification of such roles of engrailed
requires further experimentation involving engrailed
double mutants. If the double mutants were to exhibit imaginal disc
deformities involving compartmentalization or anterior-posterior pattering,
then the function of engrailed would
be revealed. However, it is noteworthy that engrailed
carries out its roles through complex interactions with other genes, such as hedgehog, dpp, and omb. Therefore, connecting deformities observed in the double
mutants to the exact roles of engrailed is
cursory at best; deformities observed could either be primary or secondary
effects caused by the deletion of engrailed.
Another observation made in the experiment was
the phenotypic difference between the leg imaginal discs of the wildtype larva
(Figure 3A) and En-lacZ larva (Figure
3B). Each of the three sets of adult Drosophila
legs is phenotypically different (Cruz, 1993), therefore it was suggested that
each of the leg imaginal discs should also be different in appearance. It was
also suggested that there are three phenotypically different pairs of leg
imaginal discs, each corresponding to the fore, mid, and hind legs. In fact,
the difference is noticeable in the results (Figure 3). In the leg imaginal
disc of the wildtype larva (Figure 3A), there is a greater number of internal
concentric compartments than in the En-lacZ
larva’s leg imaginal disc (Figure 3B). Consulting Cruz (1993)(Figure 1), it
was suggested that the wildtype larva’s leg imaginal disc dissected out in the
experiment corresponds to the mid-leg of the adult fly. On the other hand, the
leg imaginal disc of En-lacZ larva
has fewer numbers of internal concentric compartments than wildtype larva’s and
has a dark crescent in the center (Figure 3B). Also, it is blunter on its
dorsal end (Figure 3). Consulting Cruz (1993)(Figure 2), it was conjectured
that the imaginal disc in Figure 3B corresponds to the adult fore-leg.
Different types of leg imaginal discs were dissected out from each larva
because only one leg imaginal disc was randomly dissected out from each strain
of larva. In a future experiment, same type of leg imaginal discs should be
dissected out of wildtype and En-lacZ
larvae for better contrast in β-galatosidase reporter activity. Moreover,
all three types of leg imaginal discs should be dissected out to confirm that
there are, in fact, observable phenotypic differences among the leg imaginal
disc pairs.
Reference:
Cruz, Y. P. 1993. “Laboratory Exercise in Developmental Biology.” Academic
Press:
Gilbert, Scott. 2003. Developmental
Biology. 7th ed. Sinauer Associates:
Tyler, M. S. 1994. “Developmental Biology: A Guide for Experimental Study.”
Sinauer Associates:
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modified:
Laura Carballo & Brian Hwang