Proceedings of the National Academy of Sciences of the United States of America最新文献

Evolutionary transitions in land plant fertilization from zooidogamy to siphonogamy were characterized by transformations of male reproductive cells. Basal land plants such as bryophytes and pteridophytes have motile sperm, whereas most seed plants have nonmotile sperm, delivered by a pollen tube. Despite being seed plants, gymnosperm cycads and ginkgo uniquely form highly multiflagellated and large motile sperm within pollen tubes. However, the evolutionary state of these male reproductive cells remains unknown. We clarified the gene expression profiles of Cycas revoluta pollen tubes and motile sperm swimming toward female reproductive cells. Male cycad cells expressed fewer genes associated with transcription, translation, and related processes, which is consistent across land plants. We compared the distinctive orthologous groups (OGs) of the genes specifically expressed in sperm and pollen tubes with those in other plants. Cycad pollen tubes shared several OGs with angiosperms but possessed significantly fewer gene copies and lacked cell wall remodeling and plasma membrane-localized receptor genes that contribute to rapid and guided growth. The growth mechanism of cycad pollen tubes might be largely different from angiosperm pollen tubes. In contrast, despite their morphological uniqueness, cycad sperm shared representative OGs with angiosperm sperm cells to the same extent as egg cells. In addition, a sperm-specific histone variant may contribute to transcriptional regulation via chromatin condensation like other male gametes. As an extant gymnosperm that retains zooidogamy with pollen tubes, the cycad represents a molecular intermediate state in the transition from zooidogamy to siphonogamy, providing insight into the evolution of land plant fertilization.

Controlling the mechanical response of soft glassy materials-such as emulsions, foams, and colloidal suspensions-is key for many industrial processes. While their steady-state flow behavior is reasonably well understood, their response to complex flow histories, as encountered in operations like pumping or mixing, remains poorly known. Using a custom multiaxis shear apparatus that enables arbitrary changes in flow direction, we investigate how shear history influences the mechanical behavior of a model soft glassy system. We uncover a transient shear response orthogonal to the applied shear direction, together with an anisotropic yield surface. These effects point to an underlying anisotropic distribution of internal stresses imprinted by previous deformation. To rationalize this behavior, we use a mesoscopic elastoplastic model, demonstrating that local mechanical disorder governs the emergence of macroscopic stress-flow misalignment. Our findings offer a route to experimentally probe the distribution of local yield stresses in soft glassy materials.

Studying dopamine signaling in nonmodel organisms is crucial for understanding the broad range of behaviors not represented in traditional model systems. However, exploring new species is often hindered by a scarcity of tools suitable for nongenetic models. In this work, we introduce near-infrared catecholamine nanosensors (nIRCats) to investigate dopamine dynamics in meadow voles, a rodent species that exhibits distinct changes in social behavior and neurobiology across photoperiods. We observe increased dopamine release and release site density in voles housed in short photoperiods (which induce a social phenotype), suggesting adaptations linked to environmental changes. Moreover, pharmacological and extracellular manipulations demonstrate that short photoperiod/social voles exhibit heightened responsiveness to dopamine-increasing interventions and resilience against suppressive conditions. These findings highlight a significant association between dopamine signaling and photoperiod-driven changes in social behavior and establish nIRCats as an effective tool for expanding our understanding of dopamine dynamics across nonmodel organisms.

There hardly is a fluid mechanics phenomenon attracting more attention than the impact of a droplet, due to its undeniable beauty, many applications, and the numerous challenges it poses. One of the crucial factors turns out to be the cushioning effect of the gas surrounding the droplet. This fact, together with the observation that almost all of the relevant literature was done in air, triggers the question what would happen when the liquid was a boiling liquid, i.e., a liquid in thermal equilibrium with its own vapor, as is the case during transport of cryogenic liquids such as liquid hydrogen. To investigate precisely this question, we experimentally generate droplets in thermodynamical equilibrium with their own vapor, even before impact, such that minute energy exchanges of the droplet with its surroundings can trigger phase change. Using a frustrated total internal reflection setup, we make the exciting observation that depending on the impact speed and vapor conditions, the entrapment of vapor can be completely suppressed under boiling liquid conditions. We create a simplified model based on scaling arguments and perform numerical simulations considering both the compressible and condensable properties of the vapor layer that are in very good agreement with our experimental findings. Our results can be of great consequence to the pressures exerted during droplet impact and on an industrial scale may help better understand the loads experienced during sloshing wave impact inside cryogenic liquid containers.