Annual changes in the environment threaten survival, and numerous biological processes in mammals adjust to this challenge via seasonal encoding by the suprachiasmatic nucleus (SCN). To tune behavior according to day length, SCN neurons display unified rhythms with synchronous phasing when days are short, but will divide into two sub-clusters when days are long. The transition between SCN states is critical for maintaining behavioral responses to seasonal change, but the mechanisms regulating this form of neuroplasticity remain unclear. Here we identify that a switch in chloride transport and GABAA signaling is critical for maintaining state plasticity in the SCN network. Further, we reveal that blocking excitatory GABAA signaling locks the SCN into its long day state. Collectively, these data demonstrate that plasticity in GABAA signaling dictates how clock neurons interact to maintain environmental encoding. Further, this work highlights factors that may influence susceptibility to seasonal disorders in humans.

Autism spectrum disorders (ASDs) are characterized by impaired learning of social skills and language. Memories of how parents and other social models behave are used to guide behavioral learning. How ASD-linked genes affect the intertwined aspects of observational learning and behavioral imitation is not known. Here, we examine how disrupted expression of the ASD gene FOXP1, which causes severe impairments in speech and language learning, affects the cultural transmission of birdsong between adult and juvenile zebra finches. FoxP1 is widely expressed in striatal-projecting forebrain mirror neurons. Knockdown of FoxP1 in this circuit prevents juvenile birds from forming memories of an adult song model but does not interrupt learning how to vocally imitate a previously memorized song. This selective learning deficit is associated with potent disruptions to experience-dependent structural and synaptic plasticity in mirror neurons. Thus, FoxP1 regulates the ability to form memories essential to the cultural transmission of behavior.

Circadian rhythms are programmed by the suprachiasmatic nucleus (SCN), which relies on neuropeptide signaling to maintain daily timekeeping. Vasoactive intestinal polypeptide (VIP) is critical for SCN function, but the precise role of VIP neurons in SCN circuits is not fully established. To interrogate their contribution to SCN circuits, VIP neurons can be manipulated specifically using the DNA-editing enzyme Cre recombinase. Although the Cre transgene is assumed to be inert by itself, we find that VIP expression is reduced in both heterozygous and homozygous adult VIP-IRES-Cre mice (JAX 010908). Compared with wild-type mice, homozygous VIP-Cre mice display faster reentrainment and shorter free-running period but do not become arrhythmic in constant darkness. Consistent with this phenotype, homozygous VIP-Cre mice display intact SCN PER2::LUC rhythms, albeit with altered period and network organization. We present evidence that the ability to sustain molecular rhythms in the VIP-Cre SCN is not due to residual VIP signaling; rather, arginine vasopressin signaling helps to sustain SCN function at both intracellular and intercellular levels in this model. This work establishes that the VIP-IRES-Cre transgene interferes with VIP expression but that loss of VIP can be mitigated by other neuropeptide signals to help sustain SCN function. Our findings have implications for studies employing this transgenic model and provide novel insight into neuropeptide signals that sustain daily timekeeping in the master clock.

Studies indicate secreted cathepsins are involved in metastasis. V-ATPases, which are necessary for activating intracellular cathepsins, also play a role in metastasis and are targeted to the plasma membrane of metastatic breast cancer cells. We are interested in a connection between cell surface V-ATPases, activation of secreted cathepsins and the metastatic phenotype of MDA-MB231 cells. We investigated whether V-ATPase inhibition would reduce the activity of secreted cathepsin B and cathepsin L. Using cell lysates and conditioned media, we measured cathepsin B and L activity within and outside of the cells. We found different forms of cathepsin B and L were secreted representing the pre-pro, pro and active forms of the proteases. Cathepsin B activity was higher than cathepsin L in conditioned media and in cell lysates. V-ATPase inhibition by concanamycin A decreased cathepsin B activity in conditioned media and significantly decreased cathepsin B activity in cell lysates. Cathepsin L activity showed a slight decrease in cell lysates. Changes in the activity of secreted and intracellular cathepsins following V-ATPase inhibition were supported by changes in the amounts of pro and active forms of cathepsin B in conditioned media and cathepsins B and L in cell lysates. Overall, our data shows that inactive forms of cathepsins B and L are secreted from the MB231 cells and V-ATPase activity is important for the activation of secreted cathepsin B. This indicates a connection between cell surface V-ATPases in metastatic breast cancer cells and the function of secreted cathepsin B.

Light improves cognitive function in humans; however, the neurobiological mechanisms underlying positive effects of light remain unclear. One obstacle is that most rodent models have employed lighting conditions that cause cognitive deficits rather than improvements. Here we have developed a mouse model where light improves cognitive function, which provides insight into mechanisms underlying positive effects of light. To increase light exposure without eliminating daily rhythms, we exposed mice to either a standard photoperiod or a long day photoperiod. Long days enhanced long-term recognition memory, and this effect was abolished by loss of the photopigment melanopsin. Further, long days markedly altered hippocampal clock function and elevated transcription of Insulin-like Growth Factor2 (Igf2). Up-regulation of Igf2 occurred in tandem with suppression of its transcriptional repressor Wilm’s tumor1. Consistent with molecular de-repression of Igf2, IGF2 expression was increased in the hippocampus before and after memory training. Lastly, long days occluded IGF2-induced improvements in recognition memory. Collectively, these results suggest that light changes hippocampal clock function to alter memory, highlighting novel mechanisms that may contribute to the positive effects of light. Furthermore, this study provides insight into how the circadian clock can regulate hippocampus-dependent learning by controlling molecular processes required for memory consolidation.

Autism spectrum disorders (ASD) are characterized by impaired learning of culturally transmitted behaviors like 10 social skills, speech, and language 1-3 . These behaviors are learned by copying parents and other social models during 11 development, a two-stage process that involves forming memories of appropriate behaviors during social 12 experiences and then using those memories to guide imitation. How ASD-linked genes impair these often-13 intertwined aspects of learning is not known, thereby limiting our understanding of the developmental progression 14 of ASD and the targeting of therapeutic interventions. Here we show that these aspects of learning are dissociable 15 and that the ASD-linked gene FoxP1 selectively impairs learning from social experience, but not behavioral imitation. 16 Haploinsufficiency of FOXP1 in humans causes FOXP1 syndrome, a neurodevelopmental disorder typified by severe 17 disruptions in speech and language development, and other ASD-associated symptoms 4,5 . We tested how 18 knockdown of FoxP1 (FP1-KD) affects the cultural transmission of vocal behaviors in zebra finches, a songbird that 19 learns by memorizing and vocally copying the song of an adult 'song-tutor'. We find that FP1-KD blocks song learning20 in juvenile birds by selectively impairing their ability to encode a memory during social experiences with a song-21 tutor. These learning deficits are linked to disruptions in experience-driven structural and functional plasticity. 22However, if birds are exposed to tutor-song prior to FP1-KD, their ability to imitate that song during development is 23 unaffected. Thus, FP1-KD impairs cultural transmission of vocalizations by disrupting the ability to form appropriate 24 vocal memories, yet spares the ability to use previously acquired memories to guide vocal learning. This indicates 25 that learning from social experience may be particularly vulnerable in FOXP1 syndrome. 26 27 28Humans and other animals learn many of their complex and socially oriented behaviors by imitating more experienced 29 individuals in their environment. For example, development of spoken language is rooted in a child's ability to imitate 30 the speech patterns of their parent(s) and other adults 6-8 . This cultural transmission of behavior is impaired in many 31 neurodevelopmental disorders, most notably ASD 1-3 . However, how ASD risk genes impact behavioral imitation is still 32 not known. We sought to examine this issue by testing the role of FoxP1 in the cultural transmission of song between 33 adult and juvenile zebra finches ( Fig. 1a-d, Extended Data Fig. 1). 34 35 2 FOXP1 (forkhead-box protein 1) is one of the top ASD-associated genes, and its haploinsufficiency causes specific 36 language impairment and intellectual disability in children 5 . FoxP1 is expressed in many of the same areas of the pallium 37 and basal ganglia in mammals and songbirds 9-11 . In zebra finches, FoxP1 expression is enriched in many brain regions 38 that are known to be important for song learning [10][11][12] (Fig. ...

The sensory and physiological inputs which govern the larval-pupal transition in Drosophila, and the neuronal circuity that integrates them, are complex. Previous work from our laboratory identified a dosage-sensitive genetic interaction between the genes encoding the Rho-GEF Trio and the zinc-finger transcription factor Sequoia that interfered with the larval-pupal transition. Specifically, we reported heterozygous mutations in sequoia (seq) dominantly exacerbated the trio mutant phenotype, and this seq-enhanced trio mutant genotype blocked the transition of third instar larvae from foragers to wanderers, a requisite behavioral transition prior to pupation. In this work, we use the GAL4-UAS system to rescue this phenotype by tissue-specific trio expression. We find that expressing trio in the class IV dendritic arborization (da) sensory neurons rescues the larval-pupal transition, demonstrating the reliance of the larval-pupal transition on the integrity of these sensory neurons. As nociceptive responses also rely on the functionality of the class IV da neurons, we test mechanical nociceptive responses in our mutant and rescued larvae and find that mechanical nociception is separable from the ability to undergo the larval-pupal transition. This demonstrates for the first time that the roles of the class IV da neurons in governing two critical larval behaviors, the larval-pupal transition and mechanical nociception, are functionally separable from each other.

Daily and annual changes in light are processed by central clock circuits that control the timing of behavior and physiology. The suprachiasmatic nucleus (SCN) in the anterior hypothalamus processes daily photic inputs and encodes changes in day length (i.e., photoperiod), but the SCN circuits that regulate circadian and photoperiodic responses to light remain unclear. Somatostatin (SST) expression in the hypothalamus is modulated by photoperiod, but the role of SST in SCN responses to light has not been examined. Our results indicate that SST signaling regulates daily rhythms in behavior and SCN function in a manner influenced by sex. First, we use cell-fate mapping to provide evidence that SST in the SCN is regulated by light via de novo  Sst activation. Next, we demonstrate that Sst   -/-  mice display enhanced circadian responses to light, with increased behavioral plasticity to photoperiod, jetlag, and constant light conditions. Notably, lack of Sst   -/-  eliminated sex differences in photic responses due to increased plasticity in males, suggesting that SST interacts with clock circuits that process light differently in each sex. Sst   -/-  mice also displayed an increase in the number of retinorecipient neurons in the SCN core, which express a type of SST receptor capable of resetting the molecular clock. Last, we show that lack of SST signaling modulates central clock function by influencing SCN photoperiodic encoding, network after-effects, and intercellular synchrony in a sex-specific manner. Collectively, these results provide insight into peptide signaling mechanisms that regulate central clock function and its response to light.