The Long 3'UTR mRNA of CaMKII Is Essential for Translation-Dependent Plasticity of Spontaneous Release in Drosophila melanogaster.

A null mutation of the Drosophila calcium/calmodulin-dependent protein kinase II gene (CaMKII) was generated using homologous recombination. Null animals survive to larval and pupal stages due to a large maternal contribution of CaMKII mRNA, which consists of a short 3'-untranslated region (UTR) form lacking regulatory elements that guide local translation. The selective loss of the long 3'UTR mRNA in CaMKII-null larvae allows us to test its role in plasticity. Development and evoked function of the larval neuromuscular junction are surprisingly normal, but the resting rate of miniature excitatory junctional potentials (mEJPs) is significantly lower in CaMKII mutants. Mutants also lack the ability to increase mEJP rate in response to spaced depolarization, a type of activity-dependent plasticity shown to require both transcription and translation. Consistent with this, overexpression of miR-289 in wild-type animals blocks plasticity of spontaneous release. In addition to the defects in regulation of mEJP rate, CaMKII protein is largely lost from synapses in the mutant. All phenotypes are non-sex-specific and rescued by a fosmid containing the entire wild-type CaMKII locus, but only viability and CaMKII localization are rescued by genomic fosmids lacking the long 3'UTR. This suggests that synaptic CaMKII accumulates by two distinct mechanisms: local synthesis requiring the long 3'UTR form of CaMKII mRNA and a process that requires zygotic transcription of CaMKII mRNA. The origin of synaptic CaMKII also dictates its functionality. Locally translated CaMKII has a privileged role in regulation of spontaneous release, which cannot be fulfilled by synaptic CaMKII from the other pool.SIGNIFICANCE STATEMENT As a regulator of synaptic development and plasticity, CaMKII has important roles in both normal and pathological function of the nervous system. CaMKII shows high conservation between Drosophila and humans, underscoring the usefulness of Drosophila in modeling its function. Drosophila CaMKII-null mutants remain viable throughout development, enabling morphological and electrophysiological characterization. Although the structure of the synapse is normal, maternally contributed CaMKII does not localize to synapses. Zygotic production of CaMKII mRNA with a long 3'-untranslated region is necessary for modulating spontaneous neurotransmission in an activity-dependent manner, but not for viability. These data argue that regulation of CaMKII localization and levels by local transcriptional processes is conserved. This is the first demonstration of distinct functions for Drosophila CaMKII mRNA variants.

Effects of bisphenol A and triclocarban on brain-specific expression of aromatase in early zebrafish embryos.

Estrogen regulates numerous developmental and physiological processes. Most effects are mediated by estrogen receptors (ERs), which function as ligand-regulated transcription factors. Estrogen also regulates the activity of GPR30, a membrane-associated G protein-coupled receptor. Many different types of environmental contaminants can activate ERs; some can bind GPR30 as well. There is growing concern that exposure to some of these compounds, termed xenoestrogens, is interfering with the behavior and reproductive potential of numerous wildlife species, as well as affecting human health. Here, we investigated how two common, environmentally pervasive chemicals affect the in vivo expression of a known estrogen target gene in the brain of developing zebrafish embryos, aromatase AroB, which converts androgens to estrogens. We confirm that, like estrogen, the well-studied xenoestrogen bisphenol A (BPA, a plastics monomer), induces strong brain-specific overexpression of aromatase. Experiments using ER- and GPR30-selective modulators argue that this induction is largely through nuclear ERs. BPA induces dramatic overexpression of AroB RNA in the same subregions of the developing brain as estrogen. The antibacterial triclocarban (TCC) by itself stimulates AroB expression only slightly, but TCC strongly enhances the overexpression of AroB that is induced by exogenous estrogen. Thus, both BPA and TCC have the potential to elevate levels of aromatase and, thereby, levels of endogenous estrogens in the developing brain. In contrast to estrogen, BPA-induced AroB overexpression was suppressed by TCC. These results indicate that exposures to combinations of certain hormonally active pollutants can have outcomes that are not easily predicted from their individual effects.

Brain photoreceptor pathways contributing to circadian rhythmicity in crayfish.

Freshwater crayfish have three known photoreceptive systems: the compound eyes, extraretinal brain photoreceptors, and caudal photoreceptors. The primary goal of the work described here was to explore the contribution of the brain photoreceptors to circadian locomotory activity and define some of the underlying neural pathways. Immunocytochemical studies of the brain photoreceptors in the parastacid (southern hemisphere) crayfish Cherax destructor reveal their expression of the blue light-sensitive photopigment cryptochrome and the neurotransmitter histamine. The brain photoreceptors project to two small protocerebral neuropils, the brain photoreceptor neuropils (BPNs), where they terminate among fibers expressing the neuropeptide pigment-dispersing hormone (PDH), a signaling molecule in arthropod circadian systems. Comparable pathways are also described in the astacid (northern hemisphere) crayfish Procambarus clarkii. Despite exhibiting markedly different diurnal locomotor activity rhythms, removal of the compound eyes and caudal photoreceptors in both C. destructor and P. clarkii (leaving the brain photoreceptors intact) does not abolish the normal light/dark activity cycle in either species, nor prevent the entrainment of their activity cycles to phase shifts of the light/dark period. These results suggest, therefore, that crayfish brain photoreceptors are sufficient for the entrainment of locomotor activity rhythms to photic stimuli, and that they can act in the absence of the compound eyes and caudal photoreceptors. We also demonstrate that the intensity of PDH expression in the BPNs varies in phase with the locomotor activity rhythm of both crayfish species. Together, these findings suggest that the brain photoreceptor cells can function as extraretinal circadian photoreceptors and that the BPN represents part of an entrainment pathway synchronizing locomotor activity to environmental light/dark cycles, and implicating the neuropeptide PDH in these functions.