Imagine beyond: recent breakthroughs and next challenges in mammary gland biology and breast cancer research

On 8 December 2022 the organizing committee of the European Network for Breast Development and Cancer labs (ENBDC) held its fifth annual Think Tank meeting in Amsterdam, the Netherlands. Here, we embraced the opportunity to look back to identify the most prominent breakthroughs of the past ten years and to reflect on the main challenges that lie ahead for our field in the years to come. The outcomes of these discussions are presented in this position paper, in the hope that it will serve as a summary of the current state of affairs in mammary gland biology and breast cancer research for early career researchers and other newcomers in the field, and as inspiration for scientists and clinicians to move the field forward

The endosomal RIN2/Rab5C machinery prevents VEGFR2 degradation to control gene expression and tip cell identity during angiogenesis

Sprouting angiogenesis is key to many pathophysiological conditions, and is strongly regulated by vascular endothelial growth factor (VEGF) signaling through VEGF receptor 2 (VEGFR2). Here we report that the early endosomal GTPase Rab5C and its activator RIN2 prevent lysosomal routing and degradation of VEGF-bound, internalized VEGFR2 in human endothelial cells. Stabilization of endosomal VEGFR2 levels by RIN2/Rab5C is crucial for VEGF signaling through the ERK and PI3-K pathways, the expression of immediate VEGF target genes, as well as specification of angiogenic ‘tip’ and ‘stalk’ cell phenotypes and cell sprouting. Using overexpression of Rab mutants, knockdown and CRISPR/Cas9-mediated gene editing, and live-cell imaging in zebrafish, we further show that endosomal stabilization of VEGFR2 levels is required for developmental angiogenesis in vivo. In contrast, the premature degradation of internalized VEGFR2 disrupts VEGF signaling, gene expression, and tip cell formation and migration. Thus, an endosomal feedforward mechanism maintains receptor signaling by preventing lysosomal degradation, which is directly linked to the induction of target genes and cell fate in collectively migrating cells during morphogenesis

Lysyl oxidase-like 3b is critical for proliferation of chondrogenic progenitor cells during Zebrafish craniofacial development

Vertebrate craniofacial development requires coordinated morphogenetic interactions between the extracellular matrix (ECM) and the differentiating chondrocytes essential for cartilage formation. Recent studies reveal a critical role for specific lysyl oxidases in ECM integrity required for embryonic development. We now demonstrate that loxl3b is abundantly expressed within the head mesenchyme of the zebrafish and is critically important for maturation of neural crest derived cartilage elements. Histological and ultrastructural analyses of cartilage elements in loxl3b morphant embryos reveal abnormal maturation of cartilage and altered chondrocyte morphology. Spatiotemporal analysis of craniofacial markers in loxl3b morphant embryos shows that cranial neural crest cells migrate normally into the developing pharyngeal arches but that differentiation and condensation markers are aberrantly expressed. We further show that the loxl3b morphant phenotype is not due to P53 mediated cell death but likely to be due to reduced chondrogenic progenitor cell proliferation within the pharyngeal arches. Taken together, these data demonstrate a novel role for loxl3b in the maturation of craniofacial cartilage and can provide new insight into the specific genetic factors important in the pathogenesis of craniofacial birth defects. © 2011 International Society of Matrix Biology