Actin-capping protein regulates actomyosin contractility to maintain germline architecture in C. elegans.

Actin dynamics play an important role in tissue morphogenesis, yet the control of actin filament growth takes place at the molecular level. A challenge in the field is to link the molecular function of actin regulators with their physiological function. Here, we report an in vivo role of the actin-capping protein CAP-1 in the Caenorhabditis elegans germline. We show that CAP-1 is associated with actomyosin structures in the cortex and rachis, and its depletion or overexpression led to severe structural defects in the syncytial germline and oocytes. A 60% reduction in the level of CAP-1 caused a twofold increase in F-actin and non-muscle myosin II activity, and laser incision experiments revealed an increase in rachis contractility. Cytosim simulations pointed to increased myosin as the main driver of increased contractility following loss of actin-capping protein. Double depletion of CAP-1 and myosin or Rho kinase demonstrated that the rachis architecture defects associated with CAP-1 depletion require contractility of the rachis actomyosin corset. Thus, we uncovered a physiological role for actin-capping protein in regulating actomyosin contractility to maintain reproductive tissue architecture.

Sema-3A indirectly disrupts the regeneration process of goldfish optic nerve after controlled injury.

BACKGROUND: Neurons of adult mammalian CNS are prevented from regenerating injured axons due to formation of a non-permissive environment. The retinal ganglion cells (RGC), which are part of the CNS, share this characteristic. In sharp contrast, the RGC of lower vertebrates, such as fish, are capable of re-growing injured optic nerve axons, and achieve, through a complex multi-factorial process, functional vision after injury. Semaphorin-3A (sema-3A), a member of the class 3 semaphorins known for its repellent and apoptotic activities, has previously been shown to play a key role in the formation of a non-permissive environment after CNS injury in mammalians. METHODS: The expression of sema-3A and its effect on regenerative processes in injured gold fish retina and optic nerve were investigated in this study. Unilateral optic nerve axotomy or crush was induced in goldfish. 2 microl sema-3A was injected intraviterally 48 hours post injury. Neuronal viability was measured using the lipophilic neurotracer dye 4-Di-10-Asp. Axonal regeneration was initiated using the anterograde dye dextran. Retinas and optic nerves were collected at intervals of 2, 3, 7, 14 and 28 days after the procedure. Using Western blot and immunohistochemical analysis, the expression levels of semaphorin-3A, axonal regeneration, the removal of myelin debris and macrophage invasion were studied. RESULTS: We found a decrease in sema-3A levels in the retina at an early stage after optic nerve injury, but no change in sema-3A levels in the injured optic nerve. Intravitreal injection of sema-3A to goldfish eye, shortly after optic nerve injury, led to destructive effects on several pathways of the regenerative processes, including the survival of retinal ganglion cells, axonal growth, and clearance of myelin debris from the lesion site by macrophages. CONCLUSIONS: Exogenous administration of sema-3A in fish indirectly interferes with the regeneration process of the optic nerve. The findings corroborate our previous findings in mammals, and further validate sema-3A as a key factor in the generation of a non-permissive environment after transection of the optic nerve.

Upregulation of Semaphorin 3A and the associated biochemical and cellular events in a rat model of retinal detachment.

BACKGROUND: Retinal detachment, as a result of injury or disease, is a severe disorder that may ultimately lead to complete blindness. Despite advanced surgical repair techniques, the visual acuity of patients is often limited. We investigated some of the biochemical and morphological alterations following experimental retinal detachment in laboratory animals. METHODS: Unilateral retinal detachment was induced in male Wistar rats; contralateral untreated eyes served as a control. Approximately half of the retinal area was detached by a sub-retinal injection of 5 mul Saline. The incidence and extent of the retinal detachment was evaluated using MRI analysis and fundus images. The retinas were collected at intervals of 24 hours, 7, 14 and 28 days following the procedure. Using Western blot and immunohistochemical analysis, the expression levels of Semaphorin3A, Neuropilin1, GAP43 and NF-H were studied. In addition, morphological changes in Müller and microglial cells were examined. TUNEL staining was used to assess apoptosis. RESULTS: We found that the expression level of Semaphorin3A was up-regulated and reached its peak at two time points: 24 hours and 14 days after surgery. A similar pattern of expression was found for Neuropilin1. TUNEL-positive cells, indicating apoptotic processes, were evident 24 hours post retinal detachment and increased after 7 days. On the other hand, GAP43 expression was up-regulated 14 days after retinal detachment, and further intensified 28 days post-surgery. Microglial cells were activated shortly after detachment and concentrated mostly at the inner plexiform layer. GFAP staining revealed hypertrophy of Müller cells. CONCLUSIONS: The biochemical and morphological changes suggest that apoptosis as well as axonal regrowth take place following retinal detachment. Collectively, these findings may explain the limited success following repair surgery in terms of visual acuity and physiological function of the retina. Our study may open a new approach for treatment of early phase retinal detachment, as well as improve post-operative care that may, in turn, improve the functional result of the surgery. In addition, further study is required on several other factors that may affect visual acuity, such as size and location of the detached area and the time lapse between detachment and surgery.