Inhibition of Notch signaling by the p105 and p180 subunits of Drosophila chromatin assembly factor 1 is required for follicle cell proliferation

Chromatin assembly factor 1 (CAF1), a histone chaperone that mediates the deposition of histone H3/H4 onto newly synthesized DNA, is involved in Notch signaling activation during Drosophila wing imaginal disc development. Here, we report another side of CAF1, wherein the subunits CAF1-p105 and CAF1-p180 (also known as CAF1-105 and CAF1-180, respectively) inhibit expression of Notch target genes and show this is required for proliferation of Drosophila ovarian follicle cells. Loss-of-function of either CAF1-p105 or CAF1-p180 caused premature activation of Notch signaling reporters and early expression of the Notch target Hindsight (Hnt, also known as Pebbled), leading to Cut downregulation and inhibition of follicle cell mitosis. Our studies further show Notch is functionally responsible for these phenotypes observed in both the CAF1-p105- and CAF1-p180-deficient follicle cells. Moreover, we reveal that CAF1-p105- and CAF1-p180-dependent Cut expression is essential for inhibiting Hnt expression in follicle cells during their mitotic stage. These findings together indicate a novel negative-feedback regulatory loop between Cut and Hnt underlying CAF1-p105 and CAF-p180 regulation, which is crucial for follicle cell differentiation. In conclusion, our studies suggest CAF1 plays a dual role to sustain cell proliferation by positively or negatively regulating Drosophila Notch signaling in a tissue-context-dependent manner.

The zinc-finger transcription factor Hindsight regulates ovulation competency of Drosophila follicles

Follicle rupture, the final step in ovulation, utilizes conserved molecular mechanisms including matrix metalloproteinases (Mmps), steroid signaling, and adrenergic signaling. It is still unknown how follicles become competent for follicle rupture/ovulation. Here, we identify a zinc-finger transcription factor Hindsight (Hnt) as the first transcription factor regulating follicle’s competency for ovulation in Drosophila. Hnt is not expressed in immature stage-13 follicle cells but is upregulated in mature stage-14 follicle cells, which is essential for follicle rupture/ovulation. Hnt upregulates Mmp2 expression in posterior follicle cells (essential for the breakdown of the follicle wall) and Oamb expression in all follicle cells (the receptor for receiving adrenergic signaling and inducing Mmp2 activation). Hnt’s role in regulating Mmp2 and Oamb can be replaced by its human homolog Ras-responsive element-binding protein 1 (RREB-1). Our data suggest that Hnt/RREB-1 plays conserved role in regulating follicle maturation and competency for ovulation.

The release of an egg from the ovary of a female animal is a process known as ovulation. Animals as different as humans and fruit flies ovulate in largely similar ways. Yet the systems involved in controlling ovulation are still not well understood. An egg cell develops within a collection of cells that help the egg to form properly. Together, this unit is called a follicle. During ovulation, connections between the egg and the rest of the follicle break down and the egg is eventually ejected.

Ovulation happens in response to a hormone signal from the brain. In humans, this hormone is called luteinizing hormone, whereas in flies it is called octopamine. Specialized protein molecules on the surface of the follicle cells receive these hormone signals, but can only cause ovulation in mature follicles. It was not clear what allows only mature follicles to ovulate.

Deady et al. have now used the fruit fly Drosophila melanogaster to examine ovulation to identify how the process is controlled. The results showed that a protein called Hindsight primes follicle cells for ovulation. When a follicle reaches its final stage (called stage 14 in flies), the gene for Hindsight becomes active and produces the protein. This protein then activates other genes. One of the activated genes makes a protein that receives the hormone signal, while another makes a protein that breaks down follicle cells and allows the egg to be released.

The findings of Deady et al. reveal that Hindsight is needed for ovulation in flies. Further experiments then showed that the gene for equivalent human protein can be transplanted into flies and can still prime follicles for ovulation. This indicates that the genes in humans and flies may perform the same tasks. Studying ovulation is an important part of understanding female fertility and could help scientists to understand more about human reproduction. These results may also lead to new contraceptives and improved approaches for treating infertility.

Reprint of: Equal egocentric bias in school-aged children with and without autism spectrum disorders

Egocentric bias is a core feature of autism. This phenomenon has been studied using the false belief task. However, typically developing children who pass categorical (pass or fail) false belief tasks may still show subtle egocentric bias. We examined 7- to 13-year-old children with autism spectrum disorder (ASD; n=76) or typical development (n=113) using tasks with a continuous response scale: a modified false belief task and a visual hindsight bias task. All children showed robust egocentric bias on both tasks, but no group effects were found. Our large sample size, coupled with our sensitive tasks and resoundingly null group effects, indicate that children with and without ASD possess more similar egocentric tendencies than previously reported.

Equal egocentric bias in school-aged children with and without autism spectrum disorders

Egocentric bias is a core feature of autism. This phenomenon has been studied using the false belief task. However, typically developing children who pass categorical (pass or fail) false belief tasks may still show subtle egocentric bias. We examined 7- to 13-year-old children with autism spectrum disorder (ASD; n=76) or typical development (n=113) using tasks with a continuous response scale: a modified false belief task and a visual hindsight bias task. All children showed robust egocentric bias on both tasks, but no group effects were found. Our large sample size, coupled with our sensitive tasks and resoundingly null group effects, indicate that children with and without ASD possess more similar egocentric tendencies than previously reported.

Adaptation in hindsight: dynamics and drivers shaping urban wastewater systems

Well-planned urban infrastructure should meet critical loads during its design lifetime. In order to proceed with design, engineers are forced to make numerous assumptions with very little supporting information about the development of various drivers. For the wastewater sector, these drivers include the future amount and composition of the generated wastewater, effluent requirements, technologies, prices of inputs such as energy or chemicals, and the value of outputs produced such as nutrients for fertilizer use. When planning wastewater systems, there is a lack of methods to address discrepancies between the timescales at which fundamental changes in these drivers can occur, and the long physical life expectancy of infrastructure (on the order of 25-80 years). To explore these discrepancies, we take a hindsight perspective of the long-term development of wastewater infrastructure and assess the stability of assumptions made during previous designs. Repeatedly we find that the drivers influencing wastewater loads, environmental requirements or technological innovation can change at smaller timescales than the infrastructure design lifetime, often in less than a decade. Our analysis shows that i) built infrastructure is continuously confronted with challenges it was not conceived for, ii) significant adaptation occurs during a structure's lifetime, and iii) "muddling-through" is the pre-dominant strategy for adaptive management. As a consequence, we argue, there is a need to explore robust design strategies which require the systematic use of scenario planning methods and instruments to increase operational, structural, managerial, institutional and financial flexibility. Hindsight studies, such as this one, may inform the development of robust design strategies and assist in the transition to more explicit forms of adaptive management for urban infrastructures.

Drosophila Hindsight and mammalian RREB-1 are evolutionarily conserved DNA-binding transcriptional attenuators

The Drosophila Hindsight (hnt) gene encodes a C2H2-type Zinc-finger protein, HNT, that plays multiple developmental roles including control of embryonic germ band retraction and regulation of retinal cell fate and morphogenesis. While the developmental functions of the human HNT homolog, RREB-1, are unknown, it has been shown to function as a transcriptional modulator of several tumor suppressor genes. Here we investigate HNT's functional motifs, target genes and its regulatory abilities. We show that the C-terminal region of HNT, containing the last five of its 14 Zinc fingers, binds in vitro to DNA elements very similar to those identified for RREB-1. We map HNT's in vivo binding sites on salivary gland polytene chromosomes and define, at high resolution, where HNT is bound to two target genes, hnt itself and nervy (nvy). Data from both loss-of-function and over-expression experiments show that HNT attenuates the transcription of these two targets in a tissue-specific manner. RREB-1, when expressed in Drosophila, binds to the same polytene chromosome sites as HNT, attenuates expression of the hnt and nvy genes, and rescues the germ band retraction phenotype. HNT's ninth Zinc finger has degenerated or been lost in the vertebrate lineage. We show that a HNT protein mutant for this finger can also attenuate target gene expression and rescue germ band retraction. Thus HNT and RREB-1 are functional homologs at the level of DNA binding, transcriptional regulation and developmental control.