Neither the mechanisms that govern lip morphogenesis nor the cause of cleft lip are well understood. We report that genetic inactivation of Lrp6, a co-receptor of the Wnt/β-catenin signaling pathway, leads to cleft lip with cleft palate. The activity of a Wnt signaling reporter is blocked in the orofacial primordia by Lrp6 deletion in mice. The morphological dynamic that is required for normal lip formation and fusion is disrupted in these mutants. The expression of the homeobox genes Msx1 and Msx2 is dramatically reduced in the mutants, which prevents the outgrowth of orofacial primordia, especially in the fusion site. We further demonstrate that Msx1 and Msx2 (but not their potential regulator Bmp4) are the downstream targets of the Wnt/β-catenin signaling pathway during lip formation and fusion. By contrast, a `fusion-resistant'gene, Raldh3 (also known as Aldh1a3), that encodes a retinoic acid-synthesizing enzyme is ectopically expressed in the upper lip primordia of Lrp6-deficient embryos, indicating a region-specific role of the Wnt/β-catenin signaling pathway in repressing retinoic acid signaling. Thus, the Lrp6-mediated Wnt signaling pathway is required for lip development by orchestrating two distinctively different morphogenetic movements.

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Coloboma, an ocular birth defect seen in humans and other species, is caused by incomplete closure of the optic fissure. Here, we demonstrate that genetic deletion of Lrp6, a bottleneck coreceptor in the canonical Wnt signaling pathway, results in ocular coloboma and neuroretinal patterning defects in mice. The expression of ventral neuroretinal patterning gene Vax2 was conserved but with dorsally shifted expression domains; however, the dorsal neuroretinal patterning gene Tbx5 was lost in the Lrp6-mutant eyes at embryonic day 10.5. Both Bmp4 and phosphorylated Smad 1/5/8 were also significantly attenuated in the dorsal neuroretina. In addition, the retinoic acid synthesizing enzymes Raldh1 and Raldh3 were significantly changed in the mutant eyes. Our findings suggest that defective retinal patterning causes coloboma in the Lrp6-deficient mice, and that canonical Wnt signaling plays a primary role in dorsal neuroretinal patterning and related morphogenetic movements by regulation of both Bmp and retinoic acid signaling pathways. Developmental Dynamics 237:3681-3689, 2008.

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Rationale: Iron-saturated Lf (Holo-Lactoferrin, Holo-Lf) exhibits a superior anticancer property than low iron-saturated Lf (Apo-Lf). Ferroptosis is an iron-dependent cell death characterized by the accumulation of lipid peroxidation products and lethal reactive oxygen species (ROS). Radiotherapy also exerts its therapeutic effect through ROS. Methods: The effect of different iron-saturated Lf on ferroptosis and radiotherapy were tested on triple-negative breast cancer (TNBC) cell line MDA-MB-231 and non-TNBC cell line MCF-7. Results: Holo-Lf significantly increased the total iron content, promoted ROS generation, increased lipid peroxidation end product, malondialdehyde (MDA), and enhanced ferroptosis of MDA-MB-231 cells. By contrast, Apo-Lf upregulated SLC7a11 expression, increased GSH generation and inhibited ferroptosis of MDA-MB-231 cells. However, non-TNBC MCF-7 cells were resistant to Holo-Lf-induced ferroptosis because MCF-7 cells have a higher redox balance capacity than MDA-MB-231 cells. More importantly, Holo-Lf downregulated HIF-1α expression, ameliorated the hypoxia microenvironment in subcutaneous MDA-MB-231 tumors, and promoted radiation-induced DNA damage to hypoxic MDA-MB-231 cells. Finally, the efficacy of radiotherapy to MDA-MB-231 tumors was enhanced by Holo-Lf. Conclusion: Holo-Lf could induce ferroptosis in MDA-MB-231 cells and sensitize MDA-MB-231 tumors to radiotherapy.

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