Given the potential role of lilli as a transcriptional regulator, an examination was performed to see whether the pair-rule phenotype in lilli germ-line clone (GLC) embryos corresponds to changes in the expression of early patterning genes. Examined was the spatiotemporal pattern of mRNA expression for several of these genes: the maternal coordinator gene bicoid; the gap gene hunchback; the pair-rule genes fushi tarazu, even-skipped, hairy, and runt; the segment polarity genes engrailed and wingless and the terminal gap genes tailless and huckebein. The expression patterns of bcd, hb, eve, h and run mRNA appear relatively normal. In contrast, levels of ftz mRNA were significantly lower in lilli GLC embryos than wild-type embryos at the end of cellularization. ftz expression appears normal prior to mid-cellularization, after which its distribution becomes diffuse and uniform, and it rarely accumulates in stripes. Using ftz-lacZ and hb-lacZ transgenes to determine the level of such regulation, it was found that expression of the ftz-lacZ transgene is markedly reduced in lilli GLC embryos, while that of the hb-lacZ transgene remains unimpaired. This suggests that Lilli regulates ftz gene expression at the transcriptional level. Since both ftz and lilli are required for even-numbered En stripes and odd-numbered segment formation, this disruption of ftz expression may account for the pair-rule phenotype observed in lilli GLC embryos (Tang, 2001).
In addition, hkb mRNA is either reduced or absent at the embryonic termini, while the expression of tll mRNA is largely unaffected in lilli GLC embryos. hkb establishes the anterior and posterior borders of the ventral furrow during gastrulation, and lack of hkb expression causes the mesoderm and ventral domain to extend to the poles; this domain is marked by expression of snail. Accordingly, a small extension was found of the ventral domain that expresses sna and undergoes ventral furrow formation (Tang, 2001).
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