A transcriptomic taxonomy of Drosophila circadian neurons around the clock

Many different functions are regulated by circadian rhythms, including those orchestrated by discrete clock neurons within animal brains. To comprehensively characterize and assign cell identity to the 75 pairs of Drosophila circadian neurons, we optimized a single-cell RNA sequencing method and assayed clock neuron gene expression at different times of day. The data identify at least 17 clock neuron categories with striking spatial regulation of gene expression. Transcription factor regulation is prominent and likely contributes to the robust circadian oscillation of many transcripts, including those that encode cell-surface proteins previously shown to be important for cell recognition and synapse formation during development. The many other clock-regulated genes also constitute an important resource for future mechanistic and functional studies between clock neurons and/or for temporal signaling to circuits elsewhere in the fly brain.

Internal state configures olfactory behavior and early sensory processing in Drosophila larvae

Animals exhibit different behavioral responses to the same sensory cue depending on their internal state at a given moment. How and where in the brain are sensory inputs combined with state information to select an appropriate behavior? Here, we investigate how food deprivation affects olfactory behavior in Drosophila larvae. We find that certain odors repel well-fed animals but attract food-deprived animals and that feeding state flexibly alters neural processing in the first olfactory center, the antennal lobe. Hunger differentially modulates two output pathways required for opposing behavioral responses. Upon food deprivation, attraction-mediating uniglomerular projection neurons show elevated odor-evoked activity, whereas an aversion-mediating multiglomerular projection neuron receives odor-evoked inhibition. The switch between these two pathways is regulated by the lone serotonergic neuron in the antennal lobe, CSD. Our findings demonstrate how flexible behaviors can arise from state-dependent circuit dynamics in an early sensory processing center.

A Functional Clock Within the Main Morning and Evening Neurons of D. melanogaster Is Not Sufficient for Wild-Type Locomotor Activity Under Changing Day Length

A major challenge for all organisms that live in temperate and subpolar regions is to adapt physiology and activity to different photoperiods. A long-standing model assumes that there are morning (M) and evening (E) oscillators with different photoreceptive properties that couple to dawn and dusk, respectively, and by this way adjust activity to the different photoperiods. In the fruit fly Drosophila melanogaster, M and E oscillators have been localized to specific circadian clock neurons in the brain. Here, we investigate under different photoperiods the activity pattern of flies expressing the clock protein PERIOD (PER) only in subsets of M and E oscillators. We found that all fly lines that expressed PER only in subsets of the clock neurons had difficulties to track the morning and evening in a wild-type manner. The lack of the E oscillators advanced M activity under short days, whereas the lack of the M oscillators delayed E activity under the same conditions. In addition, we found that flies expressing PER only in subsets of clock neurons showed higher activity levels at certain times of day or night, suggesting that M and E clock neurons might inhibit activity at specific moments throughout the 24 h. Altogether, we show that the proper interaction between all clock cells is important for adapting the flies’ activity to different photoperiods and discuss our findings in the light of the current literature.

Entrainment of the Drosophila clock by the visual system

Circadian clocks evolved as an adaptation to the cyclic change of day and night. To precisely adapt to this environment, the endogenous period has to be adjusted every day to exactly 24 hours by a process called entrainment. Organisms can use several external cues, called zeitgebers, to adapt. These include changes in temperature, humidity, or light. The latter is the most powerful signal to synchronize the clock in animals. Research shows that a complex visual system and circadian photoreceptors work together to adjust animal physiology to the outside world. This review will focus on the importance of the visual system for clock synchronization in the fruit fly Drosophila melanogaster. It will cover behavioral and physiological evidence that supports the importance of the visual system in light entrainment.

Neuron-specific knockouts indicate the importance of network communication to Drosophila rhythmicity

Animal circadian rhythms persist in constant darkness and are driven by intracellular transcription-translation feedback loops. Although these cellular oscillators communicate, isolated mammalian cellular clocks continue to tick away in darkness without intercellular communication. To investigate these issues in Drosophila, we assayed behavior as well as molecular rhythms within individual brain clock neurons while blocking communication within the ca. 150 neuron clock network. We also generated CRISPR-mediated neuron-specific circadian clock knockouts. The results point to two key clock neuron groups: loss of the clock within both regions but neither one alone has a strong behavioral phenotype in darkness; communication between these regions also contributes to circadian period determination. Under these dark conditions, the clock within one region persists without network communication. The clock within the famous PDF-expressing s-LNv neurons however was strongly dependent on network communication, likely because clock gene expression within these vulnerable sLNvs depends on neuronal firing or light.

Light-Mediated Circuit Switching in the Drosophila Neuronal Clock Network

The circadian clock is a timekeeper but also helps adapt physiology to the outside world. This is because an essential feature of clocks is their ability to adjust (entrain) to the environment, with light being the most important signal. Whereas cryptochrome-mediated entrainment is well understood in Drosophila, integration of light information via the visual system lacks a neuronal or molecular mechanism. Here, we show that a single photoreceptor subtype is essential for long-day adaptation. These cells activate key circadian neurons, namely the large ventral-lateral neurons (lLNvs), which release the neuropeptide pigment-dispersing factor (PDF). RNAi and rescue experiments show that PDF from these cells is necessary and sufficient for delaying the timing of the evening (E) activity in long-day conditions. This contrasts to PDF that derives from the small ventral-lateral neurons (sLNvs), which are essential for constant darkness (DD) rhythmicity. Using a cell-specific CRISPR/Cas9 assay, we show that lLNv-derived PDF directly interacts with neurons important for E activity timing. Interestingly, this pathway is specific for long-day adaptation and appears to be dispensable in equinox or DD conditions. The results therefore indicate that external cues cause a rearrangement of neuronal hierarchy, which contributes to behavioral plasticity.

Allatostatin-C/AstC-R2 Is a Novel Pathway to Modulate the Circadian Activity Pattern in Drosophila

Seven neuropeptides are expressed within the Drosophila brain circadian network. Our previous mRNA profiling suggested that Allatostatin-C (AstC) is an eighth neuropeptide and specifically expressed in dorsal clock neurons (DN1s). Our results here show that AstC is, indeed, expressed in DN1s, where it oscillates. AstC is also expressed in two less well-characterized circadian neuronal clusters, the DN3s and lateral-posterior neurons (LPNs). Behavioral experiments indicate that clock-neuron-derived AstC is required to mediate evening locomotor activity under short (winter-like) and long (summer-like) photoperiods. The AstC-Receptor 2 (AstC-R2) is expressed in LNds, the clock neurons that drive evening locomotor activity, and AstC-R2 is required in these neurons to modulate the same short photoperiod evening phenotype. Ex vivo calcium imaging indicates that AstC directly inhibits a single LNd. The results suggest that a novel AstC/AstC-R2 signaling pathway, from dorsal circadian neurons to an LNd, regulates the evening phase in Drosophila.

Cryptochrome Interacts With Actin and Enhances Eye-Mediated Light Sensitivity of the Circadian Clock in Drosophila melanogaster

Cryptochromes (CRYs) are a class of flavoproteins that sense blue light. In animals, CRYs are expressed in the eyes and in the clock neurons that control sleep/wake cycles and are implied in the generation and/or entrainment of circadian rhythmicity. Moreover, CRYs are sensing magnetic fields in insects as well as in humans. Here, we show that in the fruit fly Drosophila melanogaster CRY plays a light-independent role as "assembling" protein in the rhabdomeres of the compound eyes. CRY interacts with actin and appears to increase light sensitivity of the eyes by keeping the "signalplex" of the phototransduction cascade close to the membrane. By this way, CRY also enhances light-responses of the circadian clock.

A New Rhodopsin Influences Light-dependent Daily Activity Patterns of Fruit Flies

Rhodopsin 7 ( Rh7), a new invertebrate Rhodopsin gene, was discovered in the genome of Drosophila melanogaster in 2000, but its function has remained elusive. We generated an Rh7 null mutant ( Rh7⁰) by P element-mediated mutagenesis and found that an absence of Rh7 had significant effects on fly activity patterns during light-dark (LD) cycles: Rh7⁰ mutants exhibited less morning activity and a longer siesta than wild-type controls. Consistent with these results, we found that Rh7 appears to be expressed in a few dorsal clock neurons that have been previously implicated in the control of the siesta. We also found putative Rh7 expression in R8 photoreceptor cells of the compound eyes and in the Hofbauer-Buchner eyelets, which have been shown to control the precise timing of locomotor activity. The absence of Rh7 alone impaired neither the flies' responses to constant white light nor the ability to follow phase shifts of white LD cycles. However, in blue light (470 nm), Rh7⁰ mutants needed significantly longer to synchronize than wild-type controls, suggesting that Rh7 is a blue light-sensitive photopigment with a minor contribution to circadian clock synchronization. In combination with mutants that lacked additionally cryptochrome-based and/or eye-based light input to the circadian clock, the absence of Rh7 provoked slightly stronger effects.

Adaptation of Circadian Neuronal Network to Photoperiod in High-Latitude European Drosophilids

The genus Drosophila contains over 2,000 species that, stemming from a common ancestor in the Old World Tropics, populate today very different environments [1, 2] (reviewed in [3]). We found significant differences in the activity pattern of Drosophila species belonging to the holarctic virilis group, i.e., D. ezoana and D. littoralis, collected in Northern Europe, compared to that of the cosmopolitan D. melanogaster, collected close to the equator. These behavioral differences might have been of adaptive significance for colonizing high-latitude habitats and hence adjust to long photoperiods. Most interestingly, the flies' locomotor activity correlates with the neurochemistry of their circadian clock network, which differs between low and high latitude for the expression pattern of the blue light photopigment cryptochrome (CRY) and the neuropeptide Pigment-dispersing factor (PDF) [4-6]. In D. melanogaster, CRY and PDF are known to modulate the timing of activity and to maintain robust rhythmicity under constant conditions [7-11]. We could partly simulate the rhythmic behavior of the high-latitude virilis group species by mimicking their CRY/PDF expression patterns in a laboratory strain of D. melanogaster. We therefore suggest that these alterations in the CRY/PDF clock neurochemistry might have allowed the virilis group species to colonize high-latitude environments.

Normal vision can compensate for the loss of the circadian clock

Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY.

Twilight Dominates Over Moonlight in Adjusting Drosophila’s Activity Pattern

Light is the most important zeitgeber for the synchronization of the Drosophila melanogaster circadian clock. In nature, there is twilight, and the nights are rarely completely dark, a fact that is usually disregarded in lab experiments. Recent studies showed contrary effects of simulated twilight and moonlight on fly locomotor activity, with twilight shifting morning and evening activity into the day and moonlight shifting it into the night. A currently unanswered question is, what may happen to locomotor activity when flies are exposed to more natural conditions in which both moonlight and twilight are simulated? Our data demonstrate that flies are able to integrate twilight and moonlight. However, twilight seems to dominate over moonlight as both, morning and evening activity peaks, take place at dawn or at dusk, respectively, and not during the night. Furthermore, nocturnal activity decreases in the presence of twilight. The compound eyes are essential for this behavior, and by investigating different photoreceptor mutants, we unraveled the importance of photoreceptor cells 7 and 8 for wild-type phases of the activity peaks. To adjust nocturnal activity levels to a wild-type manner, all photoreceptor cells work together in a complex way, with rhodopsin 6 having a prominent role.

Photic entrainment in Drosophila assessed by locomotor activity recordings

Light is the most important Zeitgeber to entrain the circadian clock of the fruit fly Drosophila melanogaster to the 24-h cycle on earth. The fruit fly's circadian clock is very light sensitive, mainly because about half of the 150 clock neurons in the fly's brain express the blue-light photopigment, Cryptochrome, which provokes an immediate degradation of the clock protein Timeless upon activation by light. Consequently, Drosophila's molecular clock can reset very fast to measure the changes in environmental-lighting conditions. However, usually the responses of the molecular clock to light are not directly measured, but conclusions about entrainment of the circadian clock are drawn from recording the flies' locomotor activity rhythms. Here, we review how the flies' locomotor activity can be recorded under different light regimes and how entrainment can be analyzed and properly judged. We also summarize the influence of different recording and lighting methods on the flies' activity pattern, highlight their advantages and disadvantages, and stress general pitfalls.

Moonlight Detection by Drosophila’s Endogenous Clock Depends on Multiple Photopigments in the Compound Eyes

Many organisms change their activity on moonlit nights. Even the fruit fly Drosophila melanogaster responds to moonlight with a shift of activity into the night, at least under laboratory conditions. The compound eyes have been shown to be essential for the perception of moonlight, but it is unknown which of the 5 rhodopsins in the eyes are responsible for the observed moonlight effects. Here, we show that the outer (R1-R6) and inner (R7 and R8) photoreceptor cells in a fly’s ommatidium interact in a complex manner to provoke the moonlight effects on locomotor activity. The shift of the evening activity peak into the night depends on several rhodopsins in the inner and outer photoreceptor cells. The increase in relative nocturnal activity in response to moonlight is mainly mediated by the rhodopsin 6–expressing inner photoreceptor cell R8 together with the rhodopsin 1–expressing outer receptor cells (R1-R6), whereas just rhodopsin 1 of R1 to R6 seems necessary for increasing nocturnal activity in response to increasing daylight intensity.

The role of the KRAS G13D mutation in patients with metastatic colorectal cancer (mCRC) treated with first-line chemotherapy plus cetuximab

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Background: The CRYSTAL and OPUS studies showed that adding cetuximab (cet) to first-line chemotherapy (CT) significantly improved clinical benefit in patients (pts) with KRAS wild-type (wt) mCRC. Pts with KRAS codon 12 or 13 mutations are excluded from cet treatment. Studies suggest that not all KRAS mutations are equivalent in their biologic effects. Occasional responses and prolonged disease stabilization have been recorded following cet treatment of tumors with mainly KRAS codon 13 mutations. We investigated the influence of the most common KRAS codon 13 mutation (G13D) on clinical outcome compared with pts with other KRAS mutations or wt tumors in the CRYSTAL and OPUS trials.

Methods: KRAS mutations were detected in tumor DNA from archival material using a PCR clamping and melting curve technique. Treatment arms were compared by KRAS mutation status for progression-free (PFS) and overall survival (OS).

Results: In the CRYSTAL study of 1,063 evaluable pts 63% were KRAS wt, 6% were G13D mutant (mt) and 32% had other mutations. In the OPUS study of 315 evaluable pts, 57% were KRAS wt, 7% were G13D mt, and 36% had other mutations. Compared with KRAS wt pts those with G13D mutations did not benefit from the addition of cet to CT (Table). Data of comparisons of the G13D mutation with other KRAS mutations in these studies will be presented.

Conclusions: Patients with KRAS G13D mt tumors did not appear to benefit from the addition of cet to first-line CT for mCRC. This analysis confirms the current practice of KRAS mutation testing as the standard diagnostic tool for determining first-line treatment of mCRC pts.

[Table: see text]

[Table: see text]

Impact of early tumor shrinkage on long-term outcome in metastatic colorectal cancer (mCRC) treated with FOLFOX4 with or without cetuximab: Lessons from the OPUS trial

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Background: The measurement of tumor shrinkage at the first evaluation (8 weeks) was reported to predict long-term outcome in mCRC treated with irinotecan-based chemotherapy (CT) + cetuximab (cet) in first-line and chemorefractory patients (pts). The predictive power of early tumor measurements was restricted to pts treated with CT + cet compared with CT alone but isn't known for cet with other CT regimens. This was investigated in pts treated with the FOLFOX4 regimen ± cet in the OPUS trial.

Methods: Based on the 8-weekly radiological assessments reported by the investigator and reviewed by an independent review committee, relative changes in tumor size from baseline were computed and dichotomized using a 20% relative decrease cut-off value. Kaplan-Meier curves were constructed for progression-free survival (PFS) and overall survival (OS), stratified by treatment arm and KRAS status.

Results: Tumor measurements at week 8 with KRAS status were available in 297 pts. Tumor shrinkage ≥20% was associated with significantly better PFS and OS in KRAS wild-type (wt) pts treated with FOLFOX4 + cet but not in those treated with CT alone (Table).

Conclusions: When combining cet with FOLFOX4 in first-line KRAS wt mCRC, early tumor shrinkage is associated with long-term outcome. This finding is specific for the effect of cet, confirming this drug to have distinctive and rapid effects on tumor size leading to long-term outcome measures unrelated to the effect of CT.

[Table: see text]

[Table: see text]

Radiological tumor size decrease at week 6 is a potent predictor of outcome in chemorefractory metastatic colorectal cancer treated with cetuximab (BOND trial)

BACKGROUND

Early radiological tumor shrinkage may be associated with better long-term outcome in chemorefractory metastatic colorectal cancer (cmCRC) treated with cetuximab. We aimed at validating this in a large and independent series.

PATIENTS AND METHODS

Of the 329 patients, 289 had a measurement both at baseline and week 6. Tumor shrinkage was expressed as a relative decrease compared with baseline and categorized according to a previously reported cut-off value ( approximately 10%) or used as a continuous variable.

RESULTS

Median time to progression (TTP) was 6.1 [95% confidence interval (CI) 5.1-7.2] versus 1.5 months (95% CI 1.4-1.7) in patients with [99 patients (34.3%)] or without [190 patients (65.7%)] tumor shrinkage, respectively, at week 6 [hazard ratio (HR) 0.23 (95% CI 0.17-0.32)]. The median overall survival (OS) was 13.7 (CI NA) versus 6.9 months (95% CI 6.1-7.7) [HR 0.21 (95% CI 0.14-0.32)], respectively. In a multivariate model, early tumor decrease outperformed skin toxicity as a predictor of long-term outcome.

CONCLUSIONS

Tumor shrinkage at 6 weeks is a strong predictor of TTP and OS in cmCRC patients treated with cetuximab with or without irinotecan. This suggests early tumor shrinkage is the hallmark of efficacy of cetuximab and reliably identifies the subpopulation that is sensitive to the drug. Early tumor shrinkage can be used as a marker of efficacy in clinical practice, as such or in combination.

Male-pattern baldness is common in men with X-linked recessive ichthyosis

BACKGROUND

X-linked recessive ichthyosis (XRI) is a relatively common genetic disorder of keratinization caused by deficiency in steroid sulfatase (STS) activity. STS appears to play an important role in testosterone metabolism. Therefore it has been discussed that the presence of normally functioning STS may be a presupposition for the development of androgenetic alopecia (AGA).

METHODS

Patients with the diagnosis of XRI were sent questionnaires.

RESULTS AND CONCLUSIONS

We reviewed 26 cases with XRI and noticed 11 patients with AGA in an advanced stage. The existence of two pathways for the steroid biosynthesis may be the explanation for a compensatory mechanism in XRI males. The Delta5 pathway depends on steroid sulfate activity, whereas the working Delta4 pathway produces AGA in XRI males.

Combined calcium and vitamin D3 supplementation in elderly women: confirmation of reversal of secondary hyperparathyroidism and hip fracture risk: the Decalyos II study

Vitamin D insufficiency and low calcium intake contribute to increase parathyroid function and bone fragility in elderly people. Calcium and vitamin D supplements can reverse secondary hyperparathyroidism thus preventing hip fractures, as proved by Decalyos I. Decalyos II is a 2-year, multicenter, randomized, double-masked, placebo-controlled confirmatory study. The intention-to-treat population consisted of 583 ambulatory institutionalized women (mean age 85.2 years, SD = 7.1) randomized to the calcium-vitamin D3 fixed combination group (n = 199); the calcium plus vitamin D3 separate combination group (n = 190) and the placebo group (n = 194). Fixed and separate combination groups received the same daily amount of calcium (1200 mg) and vitamin D3 (800 IU), which had similar pharmacodynamic effects. Both types of calcium-vitamin D3 regimens increased serum 25-hydroxyvitamin D and decreased serum intact parathyroid hormone to a similar extent, with levels returning within the normal range after 6 months. In a subgroup of 114 patients, femoral neck bone mineral density (BMD) decreased in the placebo group (mean = -2.36% per year, SD = 4.92), while remaining unchanged in women treated with calcium-vitamin D3 (mean = 0.29% per year, SD = 8.63). The difference between the two groups was 2.65% (95% CI = -0.44, 5.75%) with a trend in favor of the active treatment group. No significant difference between groups was found for changes in distal radius BMD and quantitative ultrasonic parameters at the os calcis. The relative risk (RR) of HF in the placebo group compared with the active treatment group was 1.69 (95% CI = 0.96, 3.0), which is similar to that found in Decalyos I (RR = 1.7; 95% CI = 1.0, 2.8). Thus, these data are in agreement with those of Decalyos I and indicate that calcium and vitamin D3 in combination reverse senile secondary hyperparathyroidism and reduce both hip bone loss and the risk of hip fracture in elderly institutionalized women.