FIP3-endosome-dependent formation of the secondary ingression mediates ESCRT-III recruitment during cytokinesis.

The final cytokinesis event involves severing of the connecting intercellular bridge (ICB) between daughter cells. FIP3-positive recycling endosomes (FIP3 endosomes) and ESCRT complexes have been implicated in mediating the final stages of cytokinesis. Here we analyse the spatiotemporal dynamics of the actin cytoskeleton, FIP3-endosome fusion and ESCRT-III localization during cytokinesis to show that the ICB narrows by a FIP3-endosome-mediated secondary ingression, whereas the ESCRT-III complex is needed only for the last scission step of cytokinesis. We characterize the role of FIP3 endosomes during cytokinesis to demonstrate that FIP3 endosomes deliver SCAMP2/3 and p50RhoGAP to the ICB during late telophase, proteins required for the formation of the secondary ingression. We also show that the FIP3-endosome-induced secondary ingression is required for the recruitment of the ESCRT-III complex to the abscission site. Finally, we characterize a FIP3-endosome-dependent regulation of the ICB cortical actin network through the delivery of p50RhoGAP. These results provide a framework for the coordinated efforts of actin, FIP3 endosomes and the ESCRTs to regulate cytokinesis and abscission.

D8/17 and CD19 expression on lymphocytes of patients with acute rheumatic fever and Tourette's disorder.

D8/17, an alloantigen found on B lymphocytes, has been reported to be elevated in patients susceptible to rheumatic fever and may be associated with autoimmune types of neuropsychiatric disorders. The pediatric-autoimmune-neuropsychiatric-disorders-associated-with-streptococci model is a putative model of pathogenesis for a group of children whose symptoms of obsessive-compulsive disorder and Tourette's disorder (TD) are abrupt and may be triggered by an infection with group A streptococci. As a test of this model, we have examined D8/17 levels on the B cells of patients with TD and acute rheumatic fever (ARF) along with those on the B cells of normal controls by flow cytometry. We have utilized several different preparations of D8/17 antibody along with a variety of secondary antibodies but have been unable to show an association with an elevated percentage of D8/17-positive, CD19-positive B cells in either ARF or TD. We did find, however, that the percentages of CD19-positive B cells in ARF and TD patients were significantly elevated compared to those in normal controls. Group A streptococcal pharyngitis patients also had an elevated percentage of CD19 B cells, however. These studies failed to confirm the utility of determining the percentage of B cells expressing the D8/17 alloantigen in ARF patients or our sample of TD patients. In contrast, the percentage of CD19-positive B cells was significantly elevated in ARF and TD patients, as well as group A streptococcal pharyngitis patients, suggesting a role for inflammation and/or autoimmunity in the pathogenesis of these disorders.