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Abstract The reef-building corals can thrive in nutrient-poor waters because of the mutualistic symbiosis between the animal hosts and their photosynthetic dinoflagellate endosymbionts. This symbiosis is threatened by climate change and other anthropogenic stressors, so that a deeper mechanistic understanding of its function is not only of great basic biological interest but also crucial for developing rational approaches to coral conservation. The small sea anemone Aiptasia is an attractive model system for studies of this symbiosis but has been limited to date by a lack of effective genetic methods. Here, we describe the use of a simple electroporation protocol to introduce various genetic constructs [plasmid DNAs, mRNAs, and short-hairpin (sh) RNAs] into Aiptasia zygotes. Plasmid-based expression of reporter constructs in the resulting larvae was highly mosaic. In contrast, electroporation of mRNAs into zygotes resulted in uniform expression within the larvae, and success rates were similar when single or multiple mRNAs were introduced. The shRNAs were effective in knocking down expression of both coelectroporated mRNAs and endogenous genes. In this way, we could confirm the previously reported role of BRACHYURY in cnidarian embryonic development. In addition, we could show that knockdown of an Aiptasia homologue of the lysosomal-associated membrane protein 1 interfered with larval uptake and/or retention of a symbiosis-compatible algal strain. The ability to use Aiptasia larvae for such reverse-genetic studies should greatly enhance the power of this model system and serve as a starting point for further development of genetic tools in Aiptasia and other cnidarians. 

Significance Studies of eukaryotic cell division have focused on the actomyosin ring, whose filaments of F-actin and myosin-II are hypothesized to generate the contractile force for ingression of the cleavage furrow. However, myosin-II has a very limited taxonomic distribution, whereas division by furrowing is much more widespread. We used the green algaChlamydomonas reinhardtiito investigate how a furrow can form without myosin-II and the potential roles of F-actin in this process. Although F-actin was associated with ingressing furrows, its complete removal only modestly delayed furrowing, suggesting that an actin-independent mechanism (possibly involving microtubules) drives furrow ingression. Such a mechanism presumably emerged early in eukaryotic evolution and may still underlie cell division in a diverse range of modern species.