Controlled chemical modifications of single-walled carbon nanotubes (SWCNTs) that tune their useful properties have been sought for multiple applications. We found that beneficial optical changes in SWCNTs resulted from introducing low concentrations of oxygen atoms. Stable covalently oxygen-doped nanotubes were prepared by exposure to ozone and then light. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than displayed by pristine semiconducting SWCNTs. Dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image than pristine SWCNTs because they give stronger near-infrared emission and do not absorb at the shifted emission wavelength.

The ability of near-infrared fluorescence imaging to detect single-walled carbon nanotubes (SWNTs) in organisms and biological tissues has been explored using Drosophila melanogaster (fruit flies). Drosophila larvae were raised on food containing ∼10 ppm of disaggregated SWNTs. Their viability and growth were not reduced by nanotube ingestion. Near-IR nanotube fluorescence was imaged from intact living larvae, and individual nanotubes in dissected tissue specimens were imaged, structurally identified, and counted to estimate a biodistribution.

A unique feature of the genus Drosophila is the formation of unusually long sperm tails. Sperm lengths of millimeters are common within this group, with the 1.8 mm sperm of D. melanogaster being fairly typical. This marked expansion in sperm length reflects an unusual aspect of spermatogenesis in these organisms: in contrast to other species in which an intraflagellar transport system is used for growth of the sperm flagellum (Scholey, 2006), Drosophila sperm axonemes are assembled in syncytial cysts by a mechanism that does not require, and is not limited by, this system (Han et al., 2003;Sarpal et al., 2003). This unusual sperm axoneme development and the resulting expansion of sperm tail length have led to distinctive features of spermatogenesis not found in other species. In D. bifurca, a special 'sperm roller' has evolved to package its 6-centimeter-long gametes (Joly et al., 2003). In D. melanogaster, a highly evolved individualization process that generates 64 individual sperm from an elongate cyst containing 64 syncytial spermatids has been identified and studied (Noguchi and Miller, 2003;Tokuyasu et al., 1972a). The distinctive molecular mechanisms needed for this process include a motile filamentous actin system (the investment, or actin, cones) that traverses the entire length of the sperm tails, removing excess cytoplasm and investing each sperm in its own plasma membrane. A specialized microtubulerich structure (the dense complex) is also associated with the sperm nuclei and functions to position the basal body and also possibly to strengthen the nuclei as they undergo extreme condensation (A. D. Tates, Cytodifferentiation during spermatogenesis in Drosophila melanogaster, PhD thesis, Rijksuniversiteit Leiden, The Netherlands, 1971) (Tokuyasu, 1974).We have identified a locus, yuri gagarin (yuri), that we show here has multiple roles in the generation of elongate individualized sperm. The gene is only highly conserved in the genus Drosophila, suggesting specialized roles in these organisms. Interestingly, yuri was initially identified through its function in another specialized organ system of insects and arthropods: the chordotonal organs. These are complex mechanosensory structures with roles in proprioception and graviperception. The first mutation at the locus, yuri c263 , was identified in a screen for mutants affecting gravitaxis. Altered gravitaxis was shown to result from perturbed expression of yuri in subsets of chordotonal neurons (Armstrong et al., 2006). The molecular functions of the locus identified here suggest that yuri mediates specialized actin-and microtubule-related activities in Drosophila tissues. ResultsThe yuri locus in D. melanogaster and other Drosophilids In addition to the cDNA (GH14032) encoding a ~30 kDa protein that we used previously (Armstrong et al., 2006), we identified 11 further yuri ESTs/cDNAs from adult testis, ovary, S2 cells and embryos through FlyBase. Sequencing of these new cDNAs established that three major transcript classes are generated from yuri (Fig...

SummaryMaintaining the proximity of centrosomes to nuclei is important in several cellular contexts, and LINC complexes formed by SUN and KASH proteins are crucial in this process. Here, we characterize the presumed Drosophila ortholog of the mammalian SUN protein, sperm-associated antigen 4 (Spag4, previously named Giacomo), and demonstrate that Spag4 is required for centriole and nuclear attachment during spermatogenesis. Production of spag4 mRNA is limited to the testis, and Spag4 protein shows a dynamic pattern of association with the germline nuclei, including a concentration of protein at the site of attachment of the single spermatid centriole. In the absence of Spag4, nuclei and centrioles or basal bodies (BBs) dissociate from each other after meiosis. This role of Spag4 in centriolar attachment does not involve either of the two KASH proteins of the Drosophila genome (Klarsicht and MSP-300), but does require the coiled-coil protein Yuri Gagarin. Yuri shows an identical pattern of localization at the nuclear surface to Spag4 during spermatogenesis, and epistasis studies show that the activities of Yuri and dynein-dynactin are downstream of spag4 in this centriole attachment pathway. The later defects in spermatogenesis seen for yuri and spag4 mutants are similar, suggesting they could be secondary to initial disruption of events at the nuclear surface.

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Myosin VI, a ubiquitously expressed unconventional myosin, has roles in a broad array of biological processes. Unusual for this motor family, myosin VI moves toward the minus (pointed) end of actin filaments. Myosin VI has two light chain binding sites that can both bind calmodulin (CaM). However unconventional myosins could use tissue-specific light chains to modify their activity. In the Drosophila testis, myosin VI is important for maintenance of moving actin structures, called actin cones, which mediate spermatid individualization. A CaM-related protein, Androcam (Acam), is abundantly expressed in the testis and like myosin VI, accumulates on these cones. We have investigated the possibility that Acam is a testis-specific light chain of Drosophila myosin VI. We find that Acam and myosin VI precisely colocalize at the leading edge of the actin cones and that myosin VI is necessary for this Acam localization. Further, myosin VI and Acam co-immunoprecipitate from the testis and interact in yeast two-hybrid assays. Finally Acam binds with high affinity to peptide versions of both myosin VI light chain binding sites. In contrast, although Drosophila CaM also shows high affinity interactions with these peptides, we cannot detect a CaM/myosin VI interaction in the testis. We conclude that Acam and not CaM acts as a myosin VI light chain in the Drosophila testis and hypothesize that it may alter the regulation of myosin VI in this tissue.The myosins constitute a superfamily of 18 classes (1 conventional and 17 unconventional) (1), all of which share sequence similarity in the motor domain. It is thought that they also share the ability to translocate along actin filaments. Myosins play roles in numerous cellular activities, such as division, endocytosis, cell movement, and organelle trafficking. In addition to the conserved motor domain, all myosins contain one or more conserved IQ motifs (consensus sequence IQXXXRGXXXR, where X is any amino acid) that bind calmodulin (CaM), 4 a ubiquitous calcium sensor protein, or CaM-like light chains (2-4). The ATPase activity and motility of unconventional myosins can be regulated by calcium binding to CaM or a CaMlike protein (5).Members of the myosin VI class appear to be unique among the unconventional myosins in their direction of translocation along actin. They move toward the pointed, or minus, end of actin filaments (6) whereas all other myosins tested move toward the barbed, or plus, end. Recent structural studies of pig myosin VI (7) indicate that this reversed directionality is associated with one of the two unique inserts in myosin VI, termed insert 2. This sequence is located between the converter region of the motor domain and the IQ motif, and its converter-proximal sequences are proposed to redirect the lever arm in the opposite direction relative to other myosins.Insert 2 is also proposed to perform a second, structural, role in myosin VI. In the pig crystal structure, its more C-terminal sequences form a continuous helix with the IQ motif, thus potentially exte...

Innate behaviors have their origins in the specification of neural fates during development. Within Drosophila, BTB (Bric-a-brac,Tramtrack, Broad) domain proteins such as Fruitless are known to play key roles in the neural differentiation underlying such responses. We previously identified a gene, which we have termed jim lovell (lov), encoding a BTB protein with a role in gravity responses. To understand more fully the behavioral roles of this gene we have investigated its function through several approaches. Transcript and protein expression patterns have been examined and behavioral phenotypes of new lov mutations have been characterized. Lov is a nuclear protein, suggesting a role as a transcriptional regulator, as for other BTB proteins. In late embryogenesis, Lov is expressed in many CNS and PNS neurons. An examination of the PNS expression indicates that lov functions in the late specification of several classes of sensory neurons. In particular, only two of the five abdominal lateral chordotonal neurons express Lov, predicting functional variation within this highly similar group. Surprisingly, Lov is also expressed very early in embryogenesis in ways that suggests roles in morphogenetic movements, amnioserosa function and head neurogenesis. The phenotypes of two new lov mutations that delete adjacent non-coding DNA regions are strikingly different suggesting removal of different regulatory elements. In lov47, Lov expression is lost in many embryonic neurons including the two lateral chordotonal neurons. lov47 mutant larvae show feeding and locomotor defects including spontaneous backward movement. Adult lov47 males perform aberrant courtship behavior distinguished by courtship displays that are not directed at the female. lov47 adults also show more defective negative gravitaxis than the previously isolated lov91Y mutant. In contrast, lov66 produces largely normal behavior but severe female sterility associated with ectopic lov expression in the ovary. We propose a negative regulatory role for the DNA deleted in lov66.

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