Highlights d Impairment of most, but not all, mitochondrial processes causes UPR mt d Conditions inducing UPR mt lead to a decrease in mitochondrial membrane potential d Decrease in mitochondrial membrane potential acts as a signal that triggers UPR mt d The MTS of ATFS-1 acts as a sensor for decreased mitochondrial membrane potential

Graphical AbstractHighlights d Impairment of most, but not all, mitochondrial processes causes UPR mt d Conditions inducing UPR mt lead to a decrease in mitochondrial membrane potential d Decrease in mitochondrial membrane potential acts as a signal that triggers UPR mt d The MTS of ATFS-1 acts as a sensor for decreased mitochondrial membrane potential

Highlights d BRCT0 and BRCT1 promote ECT2 activation during cytokinesis d BRCT2 limits ECT2 GEF activity during metaphase and anaphase d BRCT2 binding to the GEF domain and RACGAP1 facilitates a narrow RhoA zone formation d Polo-like kinase 1 (Plk1) phosphorylates BRCT0 and binds each BRCT domain

TheHydranervous system is the paradigm of a simple nerve net. Nerve cells inHydra, as in many cnidarian polyps, are organized in a nerve net extending throughout the body column. This nerve net is required for control of spontaneous behavior: elimination of nerve cells leads to polyps that do not move and are incapable of capturing and ingesting prey (Campbell, 1976). We have re-examined the structure of theHydranerve net by immunostaining fixed polyps with a novel pan-neuronal antibody that stains all nerve cells. Confocal imaging shows that there are two distinct nerve nets, one in the ectoderm and one in the endoderm, with the unexpected absence of nerve cells in the endoderm of the tentacles. The nerve nets in the ectoderm and endoderm do not contact each other. High-resolution images show that the nerve nets consist of bundles of parallel overlapping neurites. Transmission and serial block face scanning electron microscopy show that nerve bundles in the ectoderm are closely associated with ectodermal muscle processes. Nerve bundles in the endoderm are separate from muscle processes. The occurrence of bundles of neurites supports a model for continuous growth and differentiation of the nerve net by lateral addition of new nerve cells to the existing net. This model was confirmed by tracking newly differentiated nerve cells.

The Hydra nervous system is the paradigm of a “simple nerve net”. Nerve cells in Hydra, as in many cnidarian polyps, are organized in a nerve net extending throughout the body column. This nerve net is required for control of spontaneous behavior: elimination of nerve cells leads to polyps that do not move and are incapable of capturing and ingesting prey (Campbell, 1976). We have re-examined the structure of the Hydra nerve net by immunostaining fixed polyps with a novel pan-neuronal antibody that stains all nerve cells. Confocal imaging shows that there are two distinct nerve nets, one in the ectoderm and one in the endoderm, with the unexpected absence of nerve cells in the endoderm of the tentacles. The nerve nets in the ectoderm and endoderm do not contact each other. High-resolution images show that the nerve nets consist of bundles of parallel overlapping neurites. Transmission and serial block face scanning electron microscopy show that nerve bundles in the ectoderm are closely associated with ectodermal muscle processes. Nerve bundles in the endoderm are separate from muscle processes. The occurrence of bundles of neurites supports a model for continuous growth and differentiation of the nerve net by lateral addition of new nerve cells to the existing net. This model was confirmed by tracking newly differentiated nerve cells.