Grab regulates transferrin receptor recycling and iron uptake in developing erythroblasts.

Developing erythroblasts acquire massive amounts of iron through the transferrin (Tf) cycle, which involves endocytosis, sorting, and recycling of the Tf-Tf receptor (Tfrc) complex. Previous studies on the hemoglobin-deficit (hbd) mouse have shown that the exocyst complex is indispensable for the Tfrc recycling; however, the precise mechanism underlying the efficient exocytosis and recycling of Tfrc in erythroblasts remains unclear. Here, we identify the guanine nucleotide exchange factor Grab as a critical regulator of the Tf cycle and iron metabolism during erythropoiesis. Grab is highly expressed in differentiating erythroblasts. Loss of Grab diminishes the Tfrc recycling and iron uptake, leading to hemoglobinization defects in mouse primary erythroblasts, mammalian erythroleukemia cells, and zebrafish embryos. These defects can be alleviated by supplementing iron together with hinokitiol, a small-molecule natural compound that can mediate iron transport independent of the Tf cycle. Mechanistically, Grab regulates the exocytosis of Tfrc-associated vesicles by activating the GTPase Rab8, which subsequently promotes the recruitment of the exocyst complex and vesicle exocytosis. Our results reveal a critical role for Grab in regulating the Tf cycle and provide new insights into iron homeostasis and erythropoiesis.

Generation and characterization of PDGFRα-GFP knock-in mice for visualization of PDGFRα+ fibroblasts in vivo.

The platelet-derived growth factor (PDGF) and its receptor, PDGFRα, are critical for tissue development and injury repair. To track PDGFRα-expressing cells in vivo, we generated a knock-in mouse line that expresses green fluorescent protein (GFP) under the control of the PDGFRα promoter. This genetic tool enabled us to detect PDGFRα expression in various organs during both neonatal and adult stages. Additionally, we confirmed the correlation between endogenous PDGFRα and transgenic PDGFRα expression using mouse injury models, showing the potential of this genetic reporter for studying PDGFRα-mediated signaling pathways and developing therapeutic strategies. Overall, the PDGFRα-GFP knock-in mouse line serves as a valuable tool for investigating the biology of PDGFRα and its role in normal development and disease.

Spatial-temporal proliferation of hepatocytes during pregnancy revealed by genetic lineage tracing.

The maternal liver undergoes dramatic enlargement to adapt to the increased metabolic demands during pregnancy. However, the cellular sources for liver growth during pregnancy remain largely elusive. Here, we employed a proliferation recording system, ProTracer, to examine the spatial-temporal proliferation of hepatocytes during pregnancy. We discovered that during early to late pregnancy, hepatocyte proliferation initiated from zone 1, to zone 2, and lastly to zone 3, with the majority of new hepatocytes being generated in zone 2. Additionally, using single-cell RNA sequencing, we observed that Ccnd1 was highly enriched in zone 2 hepatocytes. We further applied dual-recombinase-mediated genetic lineage tracing to reveal that Ccnd1+ hepatocytes expanded preferentially during pregnancy. Moreover, we demonstrated that estrogen induces liver enlargement during pregnancy, which was abolished in Ccnd1 knockout mice. Our work revealed a unique spatial-temporal hepatocyte proliferation pattern during pregnancy, with Ccnd1+ hepatocytes in zone 2 serving as the major cellular source for hepatic enlargement.

[Clinical application of the scapular free flap extended to the upper arm].

OBJECTIVE: To apply the scapular free flap extended to the upper arm for resurfacing the face and neck, as well as the upper lip in one stage. METHODS: The scapular free flap was designed with extended portion to the posterior and interior part of the upper arm. Then the free flap was transferred to resurface the face and neck with the routine portion and to resurface the upper lip with the extended portion. RESULTS: 6 cases with extensive upper lip, facial and cervical burn scar were treated with the extended scapular free flaps. The flap size ranged from 22 cm x 11 cm to 40 cm x 9.5 cm (36.57 cm x 10.20 cm in average) for the routine portion and from 7 cm x 4 cm to 12 cm x 4 cm (10.32 cm x 3.67 cm in average) for the extended portion. All flaps survived completely. CONCLUSIONS: There are direct communicating branches ("choke vessel") between the circumflex scapular artery (CSA) and the posterior humeral circumflex artery (PHCA). When the blood supply of PHCA is cut off, the CSA can provide blood supply through the communicating branches to the upper arm skin area previously nourished by PHCA. So the blood supply of the extended portion of the scapular free flap is not only from the branches of CSA, but also from the direct communicating branches between the CSA and PHCA. The extended scapular free flap has a reliable blood supply and can be applied to construct the facial and cervical scar contraction with the extended portion to resurface the upper lip. The satisfactory result can be expected.

[Repair of the facial defects using the expanded induced prefabricated skin flap of the retroauricular and mastoid process region based on the superficial temporal vascular bundle].

OBJECTIVE: To provide an ideal method for flap prefabrication. METHODS: The superficial temporal fascial flap has been elevated based on the superficial temporal vessels during the first-stage procedure. A subcutaneous tissue pocket with appropriate site was formed in the retroauricular and mastoid process region. The fascial flap was transferred into the pocket and fixed properly. The tissue expander was placed under the fascial flap. When the expanding process has been finished, the expander was removed and the expanded induced prefabricated skin flap of the retroauricular and mastoid process region pedicled on the superficial temporal vascular bundle was elevated and transferred to repair the facial skin defect. RESULTS: There were nine cases in the group. Facial defects after resection of the melanotic nevus was repaired in 2 cases and facial defects after resection of the facial haemangioma and scar were repaired in 2 and 5 cases respectively. Pedicle length of the superficial temporal fascial flap was ranged from 5.5 cm to 7 cm (mean length 6.2 cm). The size of the fascial flaps was ranged from 4 cm x 3 cm to 7 cm x 7 cm (mean size 5.7 cm x 4.9 cm). The size of the prefabricated skin flaps was ranged from 5 cm x 5 cm to 8.0 cm x 7.5 cm (mean size 6.4 cm x 6.1 cm). The average time of the tissue expansion process is 16.1 weeks. All flaps survived postoperatively and the donor sites of the flaps were appropriated directly in 5 cases. The split-thickness skin grafting was used to recover the donor site defects in 4 cases. CONCLUSIONS: The superficial temporal fascial flap owns the following advantages: the vascular pedicle is much longer and vascular supply is plentiful, and it is convenient to transfer. Meanwhile, the skin of the retroauricular and mastoid process region is most similar to that of the face in texture, color and depth. For the patients selected strictly, the technique mentioned above is somewhat an ideal method for facial defect repair.