Understanding the protein function at the molecular, cellular, or even tissue level has allowed the advancement of wide-ranging fields, such as neurobiology, developmental biology and biomedical engineering. Observing loss-of-function phenotypes is one method for understanding the functions of particular proteins. Well-known methods for generating loss-of-function phenotypes include gene knockouts via homologous recombination, RNAi and the use of inhibitory drugs or function-blocking antibodies. However, there are some drawbacks to these methods, which can hamper the elucidation of particular protein functions. Gene knockout methods that are normally applied to embryonic stem cells, which delete or edit target genes to produce knockout (KO) organisms, cannot be applied to essential genes for developmental processes or house-keeping genes, since the loss of those genes is lethal. RNAi can specifically inactivate essential proteins, but the time-lag required to achieve the full loss-of-function phenotype depends on the target protein turnover rate. The use of drugs and function-blocking antibodies may generate artefacts or side-effects, depending on their specificity for the target protein. To overcome these problems, an optogenetic tool that can control protein inactivation in a spatiotemporal manner is desirable.