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Actin-rich protrusions in invasive epithelial cells of the mlt intestine. (A, B) Full thickness 3-D rendering of sagittal confocal sections through the intestine of 78 hpf wild type (WT) (A) and mlt (B) larvae. Actin is labeled by transgenic Lifeact-GFP expression (green). (A) In WT, the majority of the label is present in the epithelial cell apical brush border (bracket). (B) In mlt, actin-rich invadopodia-like protrusions of the basal epithelial cell membrane are detected (arrows), in addition to brush border actin (bracket). (C) Time lapse analysis of protrusion development. Single sagittal confocal scans through the intestine of a mlt larva beginning at 74 hpf. Basal invadopodia-like protrusions (arrowheads) precede cell invasion, which is first detected at 135 min. Asterisks mark invasive cells at 270 min (see also B). (D–F) Histological cross-sections through the intestine of 74 hpf immunostained mlt larvae. Basement membrane is labeled red (laminin immunostain) and actin labeled green (GFP immunostain in Lifeact-GFP transgenics). Nuclei stained blue with DAPI. Actin rich protrusions in mlt co-localize with sites of basal lamina degradation (arrowheads and insets E, F). During progression of the phenotype epithelial cells invade the tissue stroma through degraded regions of the basal lamina (asterisks in F). ap, apical epithelial cell border; ba, basal cell epithelial cell border.
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