Devarakonda, P. M. | bioRxiv Science

bioRxiv2023

F-actin and Myosin F control apicoplast elongation dynamics which drive apicoplast-centrosome association in Toxoplasma gondii

Toxoplasma gondii contains an essential plastid organelle called the apicoplast that is necessary for fatty acid, isoprenoid, and heme synthesis. Perturbations affecting apicoplast function or inheritance lead to parasite death. The apicoplast is a single copy organelle and therefore must be divided so that each daughter parasite inherits an apicoplast during cell division. In this study we identify new roles for F-actin and an unconventional myosin motor, TgMyoF, in this process. First, loss of TgMyoF and actin lead to an accumulation of apicoplast vesicles in the cytosol indicating a role for this actomyosin system in apicoplast protein trafficking or morphological integrity of the organelle. Second, live cell imaging reveals that during division the apicoplast is highly dynamic, exhibiting branched, U-shaped and linear morphologies that are dependent on TgMyoF and actin. In parasites where movement was inhibited by the depletion of TgMyoF, the apicoplast fails to associate with the parasite centrosomes. Thus, this study provides crucial new insight into mechanisms controlling apicoplast-centrosome association, a vital step in the apicoplast division cycle, which ensures that each daughter inherits a single apicoplast.

cell biology↗

bioRxiv2023

Trafficking of nuclear-encoded apicoplast proteins depends on F-actin and Myosin F in Toxoplasma gondii

Toxoplasma gondii contains an essential plastid organelle called the apicoplast that is necessary for fatty acid, isoprenoid, and heme synthesis. Perturbations affecting apicoplast function or inheritance lead to parasite death. The apicoplast is a single copy organelle and therefore must be divided so that each daughter parasite inherits an apicoplast during cell division. In this study we identify new roles for F-actin and an unconventional myosin motor, TgMyoF, in this process. First, loss of TgMyoF and actin lead to an accumulation of apicoplast vesicles in the cytosol indicating a role for this actomyosin system in apicoplast protein trafficking or morphological integrity of the organelle. Second, live cell imaging reveals that during division the apicoplast is highly dynamic, exhibiting branched, U-shaped and linear morphologies that are dependent on TgMyoF and actin. In parasites where movement was inhibited by the depletion of TgMyoF, the apicoplast fails to associate with the parasite centrosomes. Thus, this study provides crucial new insight into mechanisms controlling apicoplast-centrosome association, a vital step in the apicoplast division cycle, which ensures that each daughter inherits a single apicoplast.

cell biology↗

bioRxiv2021

An anti-ACVR1 antibody exacerbates heterotopic ossification by fibro/adipogenic progenitors in fibrodysplasia ossificans progressiva mice

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease characterized by progressive and catastrophic heterotopic ossification (HO) of skeletal muscle and associated soft tissues. FOP is caused by dominantly acting mutations in the bone morphogenetic protein (BMP) type I receptor, ACVR1 (also known as ALK2), the most prevalent of which is an arginine to histidine substitution [ACVR1(R206H)] in the glycine-serine rich intracellular domain of the receptor. A fundamental pathological consequence of FOP-causing ACVR1 receptor mutations is to enable activin A to initiate canonical BMP signaling in responsive progenitors, which drives skeletogenic commitment and HO. With the clear targets of activin A and ACVR1 identified, development of antibody therapeutics to prevent ligand-receptor interactions is an interventional approach currently being explored. Here, we developed a monoclonal blocking antibody (JAB0505) to the extracellular domain of ACVR1 and tested its ability to inhibit HO in established FOP mouse models. JAB0505 inhibited BMP-dependent gene expression in wild-type and ACVR1(R206H)-overexpressing cell lines. Strikingly, however, JAB0505 treatment markedly exacerbated injury-induced HO in two independent FOP mouse models in which ACVR1(R206H) was either broadly expressed, or more selectively expressed in fibro/adipogenic progenitors (FAPs). JAB0505 drove HO even under conditions of activin A inhibition, indicating that JAB0505 has receptor agonist activity. JAB0505-treated mice exhibited multiple, distinct foci of heterotopic lesions, suggesting an atypically broad anatomical domain of FAP recruitment to endochondral ossification. In addition, skeletogenic differentiation was both delayed and prolonged, and this was accompanied by dysregulation of FAP population growth. Collectively, alterations in the growth and differentiative properties of FAPs and FAP-derived skeletal cells are implicated in the aggravated HO phenotype. These data raise serious safety and efficacy concerns for the use of anti-ACVR1 antibodies to treat FOP patients.

developmental biology↗