OptoProfilin: A Single Component Biosensor of Applied Cellular Stress

The actin cytoskeleton is a biosensor of cellular stress and a potential prognosticator of human disease. In particular, aberrant cytoskeletal structures such as stress granules formed in response to energetic and oxidative stress are closely linked to ageing, cancer, cardiovascular disease, and viral infection. Whether these cytoskeletal phenomena can be harnessed for the development of biosensors for cytoskeletal dysfunction and, by extension, disease progression, remains an open question. In this work, we describe the design and development of an optogenetic iteration of profilin, an actin monomer binding protein with critical functions in cytoskeletal dynamics. We demonstrate that this optically activated profilin ('OptoProfilin') can act as an optically triggered biosensor of applied cellular stress in select immortalized cell lines. Notably, OptoProfilin is a single component biosensor, likely increasing its utility for experimentalists. While a large body of preexisting work closely links profilin activity with cellular stress and neurodegenerative disease, this, to our knowledge, is the first example of profilin as an optogenetic biosensor of stress-induced changes in the cytoskeleton.

The emerging tools for precisely manipulating microtubules

Cells generate a highly diverse microtubule network to carry out different activities. This network is comprised of distinct tubulin isotypes, tubulins with different post-translational modifications, and many microtubule-based structures. Defects in this complex system cause numerous human disorders. However, how different microtubule subtypes in this network regulate cellular architectures and activities remains largely unexplored. Emerging tools such as photosensitive pharmaceuticals, chemogenetics, and optogenetics enable the spatiotemporal manipulation of structures, dynamics, post-translational modifications, and cross-linking with actin filaments in target microtubule subtypes. This review summarizes the design rationale and applications of these new approaches and aims to provide a roadmap for researchers navigating the intricacies of microtubule dynamics and their post-translational modifications in cellular contexts, thereby opening new avenues for therapeutic interventions.

Rapid Optogenetic Clustering in the Cytoplasm with BcLOVclust

Protein clustering is a powerful form of optogenetic control, yet remarkably few proteins are known to oligomerize with light. Recently, the photoreceptor BcLOV4 was found to form protein clusters in mammalian cells in response to blue light, although clustering coincided with its translocation to the plasma membrane, potentially constraining its application as an optogenetic clustering module. Herein we identify key amino acids that couple BcLOV4 clustering to membrane binding, allowing us to engineer a variant that clusters in the cytoplasm and does not associate with the membrane in response to blue light. This variant-called BcLOVclust-clustered over many cycles with substantially faster clustering and de-clustering kinetics compared to the widely used optogenetic clustering protein Cry2. The magnitude of clustering could be strengthened by appending an intrinsically disordered region from the fused in sarcoma (FUS) protein, or by selecting the appropriate fluorescent protein to which it was fused. Like wt BcLOV4, BcLOVclust activity was sensitive to temperature: light-induced clusters spontaneously dissolved at a rate that increased with temperature despite constant illumination. At low temperatures, BcLOVclust and Cry2 could be multiplexed in the same cells, allowing light control of independent protein condensates. BcLOVclust could also be applied to control signaling proteins and stress granules in mammalian cells. While its usage is currently best suited in cells and organisms that can be cultured below ∼30 °C, a deeper understanding of BcLOVclust thermal response will further enable its use at physiological mammalian temperatures.

Sequence grammar underlying the unfolding and phase separation of globular proteins

Aberrant phase separation of globular proteins is associated with many diseases. Here, we use a model protein system to understand how the unfolded states of globular proteins drive phase separation and the formation of unfolded protein deposits (UPODs). We find that for UPODs to form, the concentrations of unfolded molecules must be above a threshold value. Additionally, unfolded molecules must possess appropriate sequence grammars to drive phase separation. While UPODs recruit molecular chaperones, their compositional profiles are also influenced by synergistic physicochemical interactions governed by the sequence grammars of unfolded proteins and cellular proteins. Overall, the driving forces for phase separation and the compositional profiles of UPODs are governed by the sequence grammars of unfolded proteins. Our studies highlight the need for uncovering the sequence grammars of unfolded proteins that drive UPOD formation and cause gain-of-function interactions whereby proteins are aberrantly recruited into UPODs.

Directed evolution approaches for optogenetic tool development

Photoswitchable proteins enable specific molecular events occurring in complex biological settings to be probed in a rapid and reversible fashion. Recent progress in the development of photoswitchable proteins as components of optogenetic tools has been greatly facilitated by directed evolution approaches in vitro, in bacteria, or in yeast. We review these developments and suggest future directions for this rapidly advancing field.

Novel InDel variations of the Cry2 gene are associated with litter size in Australian White sheep

Cryptochrome 2 (Cry2) gene regulates circadian rhythm and affects reproduction and pregnancy. Therefore, this study aimed to explore polymorphisms of the Cry2 gene and their associations with litter size at different parity in Australian White (AuW) ewes. Five putative insertion or deletion mutations within the Cry2 gene were selected to study their association with litter size. Two novel deletion mutations were identified in intronic region of Cry2 gene and were genotyped by agarose gel electrophoresis and DNA sequencing. The polymorphism information content (PIC) indicated that both mutations were low polymorphism in tested groups. Statistical analysis revealed that the P1-Del-6-bp was significantly correlated with litter size at third parity (P = 0.010), in which individuals with insertion/deletion (ID) genotype had larger litter size than insertion/insertion (II) genotype (P < 0.05). Whereas, the P2-Del-6-bp was significantly correlated with litter size at first parity (P = 0.036), in which individuals with insertion/insertion (II) genotype had larger litter size than insertion/deletion (ID) genotype (P < 0.05). Collectively, these findings may provide new insights to expedite molecular breeding in sheep through marker-assisted selection strategies (MAS).

A 90-day subchronic toxicity study of transgenic cotton expressing Cry1Ac, Cry2A and CP4-EPSPS proteins in Sprague-Dawley rats

Genetically engineered crops expressing insecticidal and herbicide-tolerant traits offer a new strategy for crop protection and enhanced production; however, at the same time present a challenge in terms of toxicology and safety. The current experiment presents the findings of a 90-day feeding study in Sprague-Dawley rats with transgenic cottonseed which is expressing insecticidal Cry proteins (Cry1Ac and Cry2A), and tolerant to the herbicide glyphosate. There were 100 rats in this experiment divided into 5 groups of 10 rats/sex/group. Cottonseed from transgenic and control (near-isogenic) lines was formulated into standard diets at levels of 10% and 30% (w/w). All formulated diets were nutritionally balanced. Overall appearance, feed consumption, body weight, organ weight, haematology, serum chemistry and urinalysis were comparable between control and treatment groups. In addition, there was no treatment-related difference in findings of microscopic histopathology and gross appearance of tissues. In conclusion, following the 13-week of feeding transgenic cottonseed, no treatment-related adverse effects were observed in any of the parameters measured in this experiment. Thus, this study demonstrated that transgenic cottonseeds do not cause toxicity and are nutritionally equivalent to its conventional counterpart.

Lights, cytoskeleton, action: Optogenetic control of cell dynamics

Cell biology is moving from observing molecules to controlling them in real time, a critical step towards a mechanistic understanding of how cells work. Initially developed from light-gated ion channels to control neuron activity, optogenetics now describes any genetically encoded protein system designed to accomplish specific light-mediated tasks. Recent photosensitive switches use many ingenious designs that bring spatial and temporal control within reach for almost any protein or pathway of interest. This next generation optogenetics includes light-controlled protein-protein interactions and shape-shifting photosensors, which in combination with live microscopy enable acute modulation and analysis of dynamic protein functions in living cells. We provide a brief overview of various types of optogenetic switches. We then discuss how diverse approaches have been used to control cytoskeleton dynamics with light through Rho GTPase signaling, microtubule and actin assembly, mitotic spindle positioning and intracellular transport and highlight advantages and limitations of different experimental strategies.

Cry2 Is Critical for Circadian Regulation of Myogenic Differentiation by Bclaf1-Mediated mRNA Stabilization of Cyclin D1 and Tmem176b

Circadian rhythms regulate cell proliferation and differentiation; however, little is known about their roles in myogenic differentiation. Our synchronized differentiation studies demonstrate that myoblast proliferation and subsequent myotube formation by cell fusion occur in circadian manners. We found that one of the core regulators of circadian rhythms, Cry2, but not Cry1, is critical for the circadian patterns of these two critical steps in myogenic differentiation. This is achieved through the specific interaction between Cry2 and Bclaf1, which stabilizes mRNAs encoding cyclin D1, a G1/S phase transition regulator, and Tmem176b, a transmembrane regulator for myogenic cell fusion. Myoblasts lacking Cry2 display premature cell cycle exit and form short myotubes because of inefficient cell fusion. Consistently, muscle regeneration is impaired in Cry2^-/- mice. Bclaf1 knockdown recapitulated the phenotypes of Cry2 knockdown: early cell cycle exit and inefficient cell fusion. This study uncovers a post-transcriptional regulation of myogenic differentiation by circadian rhythms.

Rhythmic Oxygen Levels Reset Circadian Clocks through HIF1α

The mammalian circadian system consists of a master clock in the brain that synchronizes subsidiary oscillators in peripheral tissues. The master clock maintains phase coherence in peripheral cells through systemic cues such as feeding-fasting and temperature cycles. Here, we examined the role of oxygen as a resetting cue for circadian clocks. We continuously measured oxygen levels in living animals and detected daily rhythms in tissue oxygenation. Oxygen cycles, within the physiological range, were sufficient to synchronize cellular clocks in a HIF1α-dependent manner. Furthermore, several clock genes responded to changes in oxygen levels through HIF1α. Finally, we found that a moderate reduction in oxygen levels for a short period accelerates the adaptation of wild-type but not of HIF1α-deficient mice to the new time in a jet lag protocol. We conclude that oxygen, via HIF1α activation, is a resetting cue for circadian clocks and propose oxygen modulation as therapy for jet lag.

Abnormal Clock Gene Expression and Locomotor Activity Rhythms in Two Month-Old Female APPSwe/PS1dE9 Mice

BACKGROUND

In addition to cognitive decline, Alzheimer's Disease (AD) is also characterized by agitation and disruptions in activity and sleep. These symptoms typically occur in the evening or night and have been referred to as 'sundowning'. They are especially difficult for carers and there are no specific drug treatments. There is increasing evidence that these symptoms reflect pathology of circadian rhythm generation and transmission.

OBJECTIVE

We investigated whether a transgenic mouse model relevant to AD (APPswe/PS1dE9) exhibits circadian alterations in locomotor activity in their home cage and whether expression of clock genes involved in the regulation of the circadian cycle is abnormal in the hippocampus and medulla-pons brain regions isolated from these mice.

RESULTS

In 2month old female mice the APPswe/PS1dE9 transgene alters levels and patterns in circadian rhythm of locomotor activity. Expression of the clock genes Per1, Per2, Cry1 and Cry2 was found to increase at night compared to day in wild-type control mice in the medulla/pons. This effect was blunted for Cry1 and Cry2 gene expression in APPswe/PS1dE9.

CONCLUSION

This study suggests altered circadian regulation of locomotor activity is abnormal in female APPswe/ PS1dE9 mice and that this alteration has biomolecular analogies in a widely available model of AD. The early age at which these effects are manifest suggests that these circadian effects may precede plaque development. The APPswe/PS1dE9 mouse genetic model may have potential to serve as a tool in understanding the neuropathology of circadian abnormalities in AD and as a model system to test novel therapeutic agents for these symptoms.