Crumbs (Crb) is an evolutionarily conserved transmembrane protein localised to the apical membrane of epithelial cells. Loss or mislocalisation of Crb is often associated with disruption of apicobasal cell polarity. crb mRNA is also apically enriched in epithelial cells, and, as shown here, accumulates in the oocyte of developing egg chambers. We narrowed down the localisation element (LE) of crb mRNA to 47 nucleotides, which form a putative stem-loop structure that may be recognised by Egalitarian (Egl). Mutations in conserved nucleotides abrogate apical transport. crb mRNA enrichment in the oocyte is affected in egl mutant egg chambers. A CRISPR-based genomic deletion of the crb locus that includes the LE disrupts asymmetric crb mRNA localisation in epithelia and prevents its accumulation in the oocyte during early stages of oogenesis, but does not affect Crb protein localisation in embryonic and follicular epithelia. However, flies lacking the LE show ectopic Crb protein expression in the nurse cells. These data suggest an additional role for the Drosophila 3'-UTR in regulating translation in a tissue-specific manner.

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Crumbs (Crb) 是一种进化上保守的跨膜蛋白，位于上皮细胞的顶膜。Crb 的丢失或错误定位通常与顶端基底细胞极性的破坏有关。crb mRNA 也在上皮细胞顶端富集，如图所示，在发育中的卵子室的卵母细胞中积累。我们将crb mRNA的定位元件 (LE)缩小到 47 个核苷酸，这形成了可能被 Egalitarian (Egl) 识别的推定茎环结构。保守核苷酸的突变消除了顶端运输。卵母细胞中crb mRNA 的富集在egl突变卵室中受到影响。基于 CRISPR 的crb基因组缺失包含 LE 的基因座破坏了上皮细胞中不对称的crb mRNA 定位，并在卵子发生的早期防止其在卵母细胞中的积累，但不影响胚胎和滤泡上皮细胞中的 Crb 蛋白定位。然而，缺乏 LE 的果蝇在护士细胞中表现出异位 Crb 蛋白表达。这些数据表明果蝇3'-UTR 在以组织特异性方式调节翻译方面的额外作用。

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