Actin filament organization in aligned prefusion myoblasts

The organization of the actin cytoskeleton in prefusion aligning myoblasts is likely to be important for their shape and interaction. We investigated actin filament organization and polarity by transmission electron microscopy (TEM) in these cells. About 84% of the filaments counted were either found in a subplasmalemma sheet up to 0.5 µm thick that was aligned with the long axis of the cell, or in protrusions. The remaining filaments were found in the cytoplasm, where they were randomly orientated and not organized into bundles. The polarity of the subplasmalemma filaments changed progressively from one end of the cell to the other. At the ends of the cells and in protrusions, the majority of filaments were organized such that their barbed ends faced the tip of the protrusion. We did not find any actin filament bundles or stress fibres in these cells. Time-lapse phase microscopy demonstrated that aligned cells were still actively migrating at the time of our TEM observations, and their direction of movement was restricted to the long axis of the cell group. The ability of these cells to locomote actively in the absence of actin filament bundles suggests that in these cells the subplasmalemma actin sheet contributes not only to cell shape but also to cell locomotion

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

The study of marine soundscapes is a growing field of research. Recording hardware is becoming more accessible; there are a number of off-the-shelf autonomous recorders that can be deployed for months at a time; software analysis tools exist as shareware; rawor preprocessed recordings are freely and publicly available. However, what is missing are catalogues of commonly recorded sounds. Sounds related to geophysical events (e.g. earthquakes) and weather (e.g. wind and precipitation), to human activities (e.g. ships) and to marine animals (e.g. crustaceans, fish and marine mammals) commonly occur. Marine mammals are distributed throughout Australia's oceans and significantly contribute to the underwater soundscape. However, due to a lack of concurrent visual and passive acoustic observations, it is often not known which species produces which sounds. To aid in the analysis of Australian and Antarctic marine soundscape recordings, a literature review of the sounds made by marine mammals was undertaken. Frequency, duration and source level measurements are summarised and tabulated. In addition to the literature review, new marine mammal data are presented and include recordings from Australia of Omura's whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long-finned pilot whales (G. melas), Fraser's dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), striped dolphins (Stenella coeruleoalba) and spinner dolphins (S. longirostris), as well as the whistles and burst-pulse sounds of Australian pygmy killer whales (Feresa attenuata). To date, this is the most comprehensive acoustic summary for marine mammal species in Australian waters