Role of a Specific P53 Binding Site in Limiting Tissue Overgrowth

The p53 protein is an important transcription factor known for maintaining tissue homeostasis by activating genes that have antiproliferative function, such as pro-apoptotic and cytostatic genes. Transcriptional activation of proapoptotic genes has displayed a fundamental role in mediating apoptosis during Drosophila development. Using ChIP-Seq and RNA-Seq methods, we have identified p53 binding sites potentially responsible for p53-mediated induction of pro-apoptotic genes following DNA damage. We have since generated fly lines with the p53 binding site deleted by CRISPR-Cas9-mediated genome editing. To study the effects of the p53 binding site knockout (p53BSKO) on tissue homeostasis, wings of the knockout fly line were dissected, mounted, and then compared against WT wings. Results show p53BSKO animals had an increase in wing size compared to that of the WT. FijiWings 2.2 macros software was used to measure wing hair (trichome) densities, which is directly proportional to cell numbers. This analysis showed that p53BSKO led to hyperplasia of the wing as compared to the WT. Our study indicated that this single P53BS is required for ensuring the right number of cells in a given tissue, likely through mediating overproliferation-induced apoptosis.

An RNAi Screen for Genes Required for Growth of Drosophila Wing Tissue

Cell division and tissue growth must be coordinated with development. Defects in these processes are the basis for a number of diseases, including developmental malformations and cancer. We have conducted an unbiased RNAi screen for genes that are required for growth in the Drosophila wing, using GAL4-inducible short hairpin RNA (shRNA) fly strains made by the Drosophila RNAi Screening Center. shRNA expression down the center of the larval wing disc using dpp-GAL4, and the central region of the adult wing was then scored for tissue growth and wing hair morphology. Out of 4,753 shRNA crosses that survived to adulthood, 18 had impaired wing growth. FlyBase and the new Alliance of Genome Resources knowledgebases were used to determine the known or predicted functions of these genes and the association of their human orthologs with disease. The function of eight of the genes identified has not been previously defined in Drosophila. The genes identified included those with known or predicted functions in cell cycle, chromosome segregation, morphogenesis, metabolism, steroid processing, transcription, and translation. All but one of the genes are similar to those in humans, and many are associated with disease. Knockdown of lin-52, a subunit of the Myb-MuvB transcription factor, or βNACtes6, a gene involved in protein folding and trafficking, resulted in a switch from cell proliferation to an endoreplication growth program through which wing tissue grew by an increase in cell size (hypertrophy). It is anticipated that further analysis of the genes that we have identified will reveal new mechanisms that regulate tissue growth during development.

Functional role of airflow-sensing hairs on the bat wing

The wing membrane of the big brown bat ( Eptesicus fuscus) is covered by a sparse grid of microscopic hairs. We showed previously that various tactile receptors (e.g., lanceolate endings and Merkel cell neurite complexes) are associated with wing-hair follicles. Furthermore, we found that depilation of these hairs decreased the maneuverability of bats in flight. In the present study, we investigated whether somatosensory signals arising from the hairs carry information about airflow parameters. Neural responses to calibrated air puffs on the wing were recorded from primary somatosensory cortex of E. fuscus. Single units showed sparse, phasic, and consistently timed spikes that were insensitive to air-puff duration and magnitude. The neurons discriminated airflow from different directions, and a majority responded with highest firing rates to reverse airflow from the trailing toward the leading edge of the dorsal wing. Reverse airflow, caused by vortices, occurs commonly in slowly flying bats. Hence, the present findings suggest that cortical neurons are specialized to monitor reverse airflow, indicating laminar airflow disruption (vorticity) that potentially destabilizes flight and leads to stall. NEW & NOTEWORTHY Bat wings are adaptive airfoils that enable demanding flight maneuvers. The bat wing is sparsely covered with sensory hairs, and wing-hair removal results in reduced flight maneuverability. Here, we report for the first time single-neuron responses recorded from primary somatosensory cortex to airflow stimulation that varied in amplitude, duration, and direction. The neurons show high sensitivity to the directionality of airflow and might act as stall detectors.

Insect Wing Membrane Topography Is Determined by the Dorsal Wing Epithelium

The Drosophila wing consists of a transparent wing membrane supported by a network of wing veins. Previously, we have shown that the wing membrane cuticle is not flat but is organized into ridges that are the equivalent of one wing epithelial cell in width and multiple cells in length. These cuticle ridges have an anteroposterior orientation in the anterior wing and a proximodistal orientation in the posterior wing. The precise topography of the wing membrane is remarkable because it is a fusion of two independent cuticle contributions from the dorsal and ventral wing epithelia. Here, through morphological and genetic studies, we show that it is the dorsal wing epithelium that determines wing membrane topography. Specifically, we find that wing hair location and membrane topography are coordinated on the dorsal, but not ventral, surface of the wing. In addition, we find that altering Frizzled Planar Cell Polarity (i.e., Fz PCP) signaling in the dorsal wing epithelium alone changes the membrane topography of both dorsal and ventral wing surfaces. We also examined the wing morphology of two model Hymenopterans, the honeybee Apis mellifera and the parasitic wasp Nasonia vitripennis. In both cases, wing hair location and wing membrane topography are coordinated on the dorsal, but not ventral, wing surface, suggesting that the dorsal wing epithelium also controls wing topography in these species. Because phylogenomic studies have identified the Hymenotera as basal within the Endopterygota family tree, these findings suggest that this is a primitive insect character.

Diet of spotted bats (Euderma maculatum) in Arizona as indicated by fecal analysis and stable isotopes

We assessed diet of spotted bats ( Euderma maculatum (J.A. Allen, 1891)) by visual analysis of bat feces and stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of bat feces, wing, hair, and insect prey. We collected 33 fecal samples from spotted bats and trapped 3755 insects where bats foraged. Lepidopterans averaged 99.6% of feces by volume; other insects were not a major component of diet. The δ13C and δ15N values of bat feces were similar to those of moths from families Noctuidae (N), Lasiocampidae (L), and Geometridae (G), but differed from Arctiidae (A) and Sphingidae (S). We used a mixing model to reconstruct diet; three families (N, L, G) represented the majority (88%–100%) of the diet with A + S representing 0%–12%. Although we compared δ13C and δ15N values of wing, hair, and feces of spotted bats, feces best represented recent diet; wing and hair were more enriched than feces by 3‰ and 6‰, respectively. This pattern was consistent with that reported for other bat species. We suggest that spotted bats persist across a wide latitudinal gradient partly because they can forage on a variety of noctuid, geometrid, and lasiocampid moths. Using visual fecal inspection with stable isotope analysis provided information on families of moths consumed by an uncommon bat species.