Drosophila melanogaster has the longest history as a genetic model system and even in the present day remains the front runner in diverse fields of biology. However, lack of a convenient method to make specified modifications to endogenous genes has been a pain in the neck for many fly geneticists for decades. Synthetic nuclease technologies, especially the CRISPR/Cas9 system, hold great promise for a breakthrough. Synthetic nucleases are programmable nucleases that can be directed to cleave a specified sequence in the genome. Deleterious mutations can be efficiently induced by expression of a synthetic nuclease that targets a gene of interest. Precise modification of the target site, such as a reporter gene knock-in, is also possible by simultaneous delivery of a synthetic nuclease and a targeting vector. Here I summarize recent advances in synthetic nuclease technologies and discuss their possible applications to Drosophila genetics.

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To achieve the precise wiring of axons in the brain required to form a fine architecture, a molecular level interaction between axons and their targets is necessary. The Drosophila visual system has a layered and columnar structure which is often found in the brain of vertebrates. With powerful genetic tools for its analysis, the Drosophila visual system provides a useful framework to examine the molecular mechanisms of axon targeting specificity. The medulla is the second optic ganglion in the Drosophila optic lobe, and is subdivided into ten layers. Among the eight photoreceptor types, R7 and R8 pass through the first optic ganglion lamina and innervate the medulla. In the medulla, R7 and R8 axons grow in a distinct manner to reach their final target layers: M6 and M3, respectively. The axons from R7 and R8 take characteristic steps to extend toward their target layer. In this review, we discuss the formation of the Drosophila optic lobe and the molecular mechanisms of layer specific targeting of R8 axons in the medulla. Fundamental and comprehensive understanding of the crosstalk of growing axons and target regions in the Drosophila optic lobe will elucidate the general principles applicable to more complex nervous systems.

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The antennal lobe (AL) of Drosophila is the first olfactory processing center in which olfactory input and output are spatially organized into distinct channels via glomeruli to form a discrete neural map. In each glomerulus, the axons of a single type of olfactory receptor neurons (ORNs) synapse with the dendrites of a single type of projection neurons (PNs). The AL is an ideal place to study how the wiring specificity between specific types of ORNs and PNs is established during development. During the past two decades, the involvement of diverse molecules in the specification and patterning of ORNs and PNs has been reported. Furthermore, local interneurons—another component of glomeruli—have been recently catalogued and their functions have been gradually dissected. Although there is accumulating knowledge about the involvement of these three cell types in the wiring specificity of the olfactory system, in this review, we focus especially on the development of PN dendrites.

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The insect steroid hormone ecdysteroid plays pivotal roles in the temporal coordination of development, represented by molting and metamorphosis. During the larval stages, ecdysteroid is biosynthesized from dietary cholesterol by several ecdysteroidogenic enzymes in the specialized endocrine organ called the prothoracic gland (PG). As ecdysteroid biosynthesis in the PG is affected by several environmental cues, such as photoperiod and nutrition, a fundamental question is how the ecdysteroid biosynthesis pathway is controlled in response to environmental cues. In this review, we briefly summarize recent topics on the regulatory mechanisms of ecdysteroid biosynthesis, especially the neuronal regulatory mechanism, in the fruit fly Drosophila melanogaster. The implications from studies with other insects are also discussed.

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Buergeria japonica is a common frog species distributed throughout almost all islands in Ryukyu Archipelago. Because of their exceptionally wide distribution and higher physiological tolerance comparing to the other anurans, their demographic history and formation of distribution are intrinsic topics in the herpetological fauna of Ryukyu. Microsatellite marker is ideal genetic marker for such studies at inter- and intra-population level. We therefore developed microsatellite markers of B. japonica utilizing Ion PGM™ sequencing. As a result of the screening, we developed a total of 14 polymorphic markers. To test availabilities of these markers, we genotyped four island populations. The total number of alleles and expected hetelozygosities per locus ranged from 4 to 21 and 0.00 to 0.864, respectively. The phylogenetic relationship among the four populations based on the genetic distances of these markers was congruent with general divergence pattern of amphibians and reptiles in Ryukyu area. These markers developed in this study are considered to be useful for future studies about phylogeography and demography of this species.

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