STED imaging of endogenously tagged ARF GTPases reveals their distinct nanoscale localizations

ADP-ribosylation factor (ARF) GTPases are major regulators of cellular membrane homeostasis. High sequence similarity and multiple, possibly redundant functions of the five human ARFs make investigating their function a challenging task. To shed light on the roles of the different Golgi-localized ARF members in membrane trafficking, we generated CRISPR-Cas9 knockins (KIs) of type I (ARF1 and ARF3) and type II ARFs (ARF4 and ARF5) and mapped their nanoscale localization with stimulated emission depletion (STED) super-resolution microscopy. We find ARF1, ARF4, and ARF5 on segregated nanodomains on the cis-Golgi and ER-Golgi intermediate compartments (ERGIC), revealing distinct roles in COPI recruitment on early secretory membranes. Interestingly, ARF4 and ARF5 define Golgi-tethered ERGIC elements decorated by COPI and devoid of ARF1. Differential localization of ARF1 and ARF4 on peripheral ERGICs suggests the presence of functionally different classes of intermediate compartments that could regulate bi-directional transport between the ER and the Golgi. Furthermore, ARF1 and ARF3 localize to segregated nanodomains on the trans-Golgi network (TGN) and are found on TGN-derived post-Golgi tubules, strengthening the idea of distinct roles in post-Golgi sorting. This work provides the first map of the nanoscale organization of human ARF GTPases on cellular membranes and sets the stage to dissect their numerous cellular roles.

[Gastric leiomyoblastoma: literature review and report of a case]

Leiomyoblastoma is a rare, smooth muscle tumor of the stomach that occurs chiefly in the antrum. We present the case of a 51 year old man suffering from asthenia and mild upper abdominal pain. Investigations showed a big exculcerated tumor of the lesser gastric curvature. He underwent a subtotal gastrectomy for a non-metastasizing leiomyoblastoma, grade 1. But already 5 months later, he developed an invasive non-resectable local recurrence of high grade malignancy and died 3 month after a second look. Those tumors affect middle-aged patients who present usually upper gastrointestinal bleeding or peptic ulcer-like symptoms. Although the large majority of leiomyoblastoma are benign, malignancy occurs in up to 10% of cases. A large surgical resection of the tumor (including the total thickness of the gastric wall) or a partial gastrectomy is recommended.