ZFH-2 is required for Drosophila ovarian follicle development and is expressed at the band/interband boundaries of polytene chromosomes.

The transcription factor ZFH-2 has well-documented roles in Drosophila neurogenesis and other developmental processes. Here we provide the first evidence that ZFH-2 has a role in oogenesis. We demonstrate that ZFH-2 is expressed in the wild-type ovary and that a loss of zfh-2 function produces a mutant ovary phenotype where egg chambers are reduced in number and fused. We also show that a loss of zfh-2 function can suppress a daughterless loss-of-function ovary phenotype suggesting a possible genetic relationship between these two genes in the ovary. We also show that ZFH-2 is located at the boundary between bands and interbands on polytene chromosomes and that at a subset of these sites ZFH-2 colocalizes with the insulator/promoter cofactor CP190.

Zfh-2 facilitates Notch-induced apoptosis in the CNS and appendages of Drosophila melanogaster.

Apoptosis is a fundamental remodeling process for most tissues during development. In this manuscript we examine a pro-apoptotic function for the Drosophila DNA binding protein Zfh-2 during development of the central nervous system (CNS) and appendages. In the CNS we find that a loss-of-function zfh-2 allele gives an overall reduction of apoptotic cells in the CNS, and an altered pattern of expression for the axonal markers 22C10 and FasII. This same loss-of-function zfh-2 allele causes specific cells in the NB7-3 lineage of the CNS that would normally undergo apoptosis to be inappropriately maintained, whereas a gain-of-function zfh-2 allele has the opposite effect, resulting in a loss of normal NB 7-3 progeny. We also demonstrate that Zfh-2 and Hunchback reciprocally repress each other's gene expression which limits apoptosis to later born progeny of the NB7-3 lineage. Apoptosis is also required for proper segmentation of the fly appendages. We find that Zfh-2 co-localizes with apoptotic cells in the folds of the imaginal discs and presumptive cuticular joints. A reduction of Zfh-2 levels with RNAi inhibits expression of the pro-apoptotic gene reaper, and produces abnormal joints in the leg, antenna and haltere. Apoptosis has previously been shown to be activated by Notch signaling in both the NB7-3 CNS lineage and the appendage joints. Our results indicate that Zfh-2 facilitates Notch-induced apoptosis in these structures.

Serotonergic Modulation Enables Pathway-Specific Plasticity in a Developing Sensory Circuit in Drosophila.

How experiences during development cause long-lasting changes in sensory circuits and affect behavior in mature animals are poorly understood. Here we establish a novel system for mechanistic analysis of the plasticity of developing neural circuits by showing that sensory experience during development alters nociceptive behavior and circuit physiology in Drosophila larvae. Despite the convergence of nociceptive and mechanosensory inputs on common second-order neurons (SONs), developmental noxious input modifies transmission from nociceptors to their SONs, but not from mechanosensors to the same SONs, which suggests striking sensory pathway specificity. These SONs activate serotonergic neurons to inhibit nociceptor-to-SON transmission; stimulation of nociceptors during development sensitizes nociceptor presynapses to this feedback inhibition. Our results demonstrate that, unlike associative learning, which involves inputs from two sensory pathways, sensory pathway-specific plasticity in the Drosophila nociceptive circuit is in part established through feedback modulation. This study elucidates a novel mechanism that enables pathway-specific plasticity in sensory systems. VIDEO ABSTRACT.

Sensory integration and neuromodulatory feedback facilitate Drosophila mechanonociceptive behavior.

Nociception is an evolutionarily conserved mechanism to encode and process harmful environmental stimuli. Like most animals, Drosophila melanogaster larvae respond to a variety of nociceptive stimuli, including noxious touch and temperature, with stereotyped escape responses through activation of multimodal nociceptors. How behavioral responses to these different modalities are processed and integrated by the downstream network remains poorly understood. By combining trans-synaptic labeling, ultrastructural analysis, calcium imaging, optogenetics and behavioral analyses, we uncovered a circuit specific for mechanonociception but not thermonociception. Notably, integration of mechanosensory input from innocuous and nociceptive sensory neurons is required for robust mechanonociceptive responses. We further show that neurons integrating mechanosensory input facilitate primary nociceptive output by releasing short neuropeptide F, the Drosophila neuropeptide Y homolog. Our findings unveil how integration of somatosensory input and neuropeptide-mediated modulation can produce robust modality-specific escape behavior.

H2O2-Sensitive Isoforms of Drosophila melanogaster TRPA1 Act in Bitter-Sensing Gustatory Neurons to Promote Avoidance of UV During Egg-Laying.

The evolutionarily conserved TRPA1 channel can sense various stimuli including temperatures and chemical irritants. Recent results have suggested that specific isoforms of Drosophila TRPA1 (dTRPA1) are UV-sensitive and that their UV sensitivity is due to H2O2 sensitivity. However, whether such UV sensitivity served any physiological purposes in animal behavior was unclear. Here, we demonstrate that H2O2-sensitive dTRPA1 isoforms promote avoidance of UV when adult Drosophila females are selecting sites for egg-laying. First, we show that blind/visionless females are still capable of sensing and avoiding UV during egg-laying when intensity of UV is high yet within the range of natural sunlight. Second, we show that such vision-independent UV avoidance is mediated by a group of bitter-sensing neurons on the proboscis that express H2O2-sensitive dTRPA1 isoforms. We show that these bitter-sensing neurons exhibit dTRPA1-dependent UV sensitivity. Importantly, inhibiting activities of these bitter-sensing neurons, reducing their dTRPA1 expression, or reducing their H2O2-sensitivity all significantly reduced blind females' UV avoidance, whereas selectively restoring a H2O2-sensitive isoform of dTRPA1 in these neurons restored UV avoidance. Lastly, we show that specifically expressing the red-shifted channelrhodopsin CsChrimson in these bitter-sensing neurons promotes egg-laying avoidance of red light, an otherwise neutral cue for egg-laying females. Together, these results demonstrate a physiological role of the UV-sensitive dTRPA1 isoforms, reveal that adult Drosophila possess at least two sensory systems for detecting UV, and uncover an unexpected role of bitter-sensing taste neurons in UV sensing.

Drosophila TRPA1 isoforms detect UV light via photochemical production of H2O2.

The transient receptor potential A1 (TRPA1) channel is an evolutionarily conserved detector of temperature and irritant chemicals. Here, we show that two specific isoforms of TRPA1 in Drosophila are H2O2 sensitive and that they can detect strong UV light via sensing light-induced production of H2O2. We found that ectopic expression of these H2O2-sensitive Drosophila TRPA1 (dTRPA1) isoforms conferred UV sensitivity to light-insensitive HEK293 cells and Drosophila neurons, whereas expressing the H2O2-insensitive isoform did not. Curiously, when expressed in one specific group of motor neurons in adult flies, the H2O2-sensitive dTRPA1 isoforms were as competent as the blue light-gated channelrhodopsin-2 in triggering motor output in response to light. We found that the corpus cardiacum (CC) cells, a group of neuroendocrine cells that produce the adipokinetic hormone (AKH) in the larval ring gland endogenously express these H2O2-sensitive dTRPA1 isoforms and that they are UV sensitive. Sensitivity of CC cells required dTRPA1 and H2O2 production but not conventional phototransduction molecules. Our results suggest that specific isoforms of dTRPA1 can sense UV light via photochemical production of H2O2. We speculate that UV sensitivity conferred by these isoforms in CC cells may allow young larvae to activate stress response--a function of CC cells--when they encounter strong UV, an aversive stimulus for young larvae.

Egg-laying demand induces aversion of UV light in Drosophila females.

Drosophila melanogaster females are highly selective about the chemosensory quality of their egg-laying sites, an important trait that promotes the survival and fitness of their offspring. How egg-laying females respond to UV light is not known, however. UV is a well-documented phototactic cue for adult Drosophila, but it is an aversive cue for larvae. Here, we show that female flies exhibit UV aversion in response to their egg-laying demand. First, females exhibit egg-laying aversion of UV: they prefer to lay eggs on dark sites when choosing between UV-illuminated and dark sites. Second, they also exhibit movement aversion of UV: positional tracking of single females suggests that egg-laying demand increases their tendency to turn away from UV. Genetic manipulations of the retina suggest that egg-laying and movement aversion of UV are both mediated by the inner (R7) and not the outer (R1-R6) photoreceptors. Finally, we show that the Dm8 amacrine neurons, a synaptic target of R7 photoreceptors and a mediator of UV spectral preference, are dispensable for egg-laying aversion but essential for movement aversion of UV. This study suggests that egg-laying demand can temporarily convert UV into an aversive cue for female Drosophila and that R7 photoreceptors recruit different downstream targets to control different egg-laying-induced behavioral modifications.

Mechanosensitive neurons on the internal reproductive tract contribute to egg-laying-induced acetic acid attraction in Drosophila.

Selecting a suitable site to deposit their eggs is an important reproductive need of Drosophila females. Although their choosiness toward egg-laying sites is well documented, the specific neural mechanism that activates females' search for attractive egg-laying sites is not known. Here, we show that distention and contraction of females' internal reproductive tract triggered by egg delivery through the tract plays a critical role in activating such search. We found that females start to exhibit acetic acid (AA) attraction prior to depositing each egg but no attraction when they are not laying eggs. Artificially distending the reproductive tract triggers AA attraction in non-egg-laying females, whereas silencing the mechanosensitive neurons we identified that can sense the contractile status of the tract eliminates such attraction. Our work uncovers the circuit basis of an important reproductive need of Drosophila females and provides a simple model for dissecting the neural mechanism that underlies a reproductive need-induced behavioral modification.