Biology subjects

Borchers, A.-C.

Publications and source records attributed to Borchers, A.-C..

3 recordsLinked to original sources

bioRxiv2026

SACHET: seeded contour tracking measures Rab conversion kinetics on individual endosomes in live cells

Membrane-labeled endosomes appear as hollow rings in a projection; they move, deform and exchange their coat, which population trackers (tools that detect every object of one kind and link the detections across frames) are not designed to follow. Here we introduce SACHET (Seeded Adaptive Contour & Hollow Endosome Tracking), a human-supervised Fiji tool that tracks one endosome at a time. On simulated ground truth it localizes the center to 10 nm, recovers transition time constants and lags without bias and holds the target among touching neighbors; comparisons with tuned TrackMate and Cellpose delineate where each is superior. In crowded spinning-disk projections, TrackMate followed one of seven marked Rab5-to-Rab7 conversions; supervised SACHET followed all 37. SACHET thus provides a stable per-endosome frame in which membrane morphology and protein exchange can be quantified: in five cell lines the conversion toggles like a digital switch within seconds to minutes, differing between lines.

cell biology↗

bioRxiv2026

ATG16L2 creates a VAIL-dedicated heterodimer with ATG16L1

The ATG8 conjugation machinery supports both canonical autophagy, in which ATG8 proteins are lipidated on forming autophagosomes, and CASM, in which ATG8 proteins are conjugated to stressed single-membrane compartments. How cells allocate this shared machinery between these competing membrane programs remains unclear. Here, we identify ATG16L2 as a specialized regulator of V-ATPase-responsive ATG8 lipidation (atg8ylation). ATG16L2 does not form stable homodimers and is inactive in the absence of ATG16L1, but it becomes functional through heterodimerization with ATG16L1. The ATG16L1-ATG16L2 heterodimer constitutes a VAIL-competent E3-like complex that is excluded from WIPI2-positive autophagic membranes but readily recruited to stressed lysosomes. ATG16L2 also confers VAIL activity onto the otherwise VAIL-deficient ATG16L1 isoform. We propose that ATG16L1 homodimers and ATG16L1-ATG16L2 heterodimers represent alternative assemblies of the ATG8 conjugation machinery: ATG16L1 homodimers are dedicated to WIPI2-positive autophagic membranes, whereas ATG16L1-ATG16L2 heterodimers containing either ATG16L1 isoform form a VAIL-selective assembly.

molecular biology↗

bioRxiv2023

Regulatory sites in the Mon1-Ccz1 complex control Rab5 to Rab7 transition and endosome maturation

Maturation from early to late endosomes depends on the exchange of their marker proteins Rab5 to Rab7. This requires Rab7 activation by its specific guanine nucleotide exchange factor (GEF) Mon1-Ccz1. Efficient GEF activity of this complex on membranes depends on Rab5, thus driving Rab-exchange on endosomes. However, molecular details on the role of Rab5 in Mon1-Ccz1 activation are unclear. Here we identify key features in Mon1 involved in GEF regulation. We show that the intrinsically disordered N-terminal domain of Mon1 autoinhibits Rab5-dependent GEF-activity on membranes. Consequently, Mon1 truncations result in higher GEF activity in vitro, and a shift from Rab5 to more Rab7 positive structures in Drosophila nephrocytes and yeast, suggesting faster endosomal maturation. Using modeling, we further identify a conserved Rab5 binding site in Mon1. Mutations impairing Rab5 interaction result in poor GEF activity on membranes and growth defects in vivo. Our analysis provides a framework to understand the mechanism of Rab-conversion and organelle maturation along the endomembrane system. SummaryTransport of proteins via the endolysosomal pathway requires Rab5 on early endosomes, which is replaced by Rab7 on late endosomes. Here, we identify distinct regulatory sites in the Rab7 activator, the Mon1-Ccz1 complex, shedding light on the regulation of Rab5 to Rab7 transition.

cell biology↗