Fat2 is an atypical cadherin with a large extracellular domain containing multiple cadherin repeats. Although members of the Fat family have been implicated in organ development, the role of Fat2 in neural development remains poorly understood. Here, we investigated the function of Fat2 in zebrafish, focusing on its involvement in the development of cerebellar granule cells. Granule cells in the rostromedial cerebellum project their axons, known as parallel fibers, to Purkinje cell dendrites. In contrast, granule cells in the caudolateral cerebellum project their axons to Purkinje cells and further extend them caudally to innervate crest cells, Purkinje-like neurons located in the dorsal hindbrain region called the medio-octaval lateralis. We found that in fat2 mutants, axons of caudolateral cerebellar granule cells projecting to crest cells exhibit abnormal branching and frequently overshoot their targets. These results indicate that Fat2 is required for proper axon formation in at least a subset of cerebellar granule cells.
Changes in sperm motility can serve as an early indicator of reproductive effects caused by environmental chemicals or genetic perturbations. However, sperm motility is highly sensitive to external factors such as osmolarity, ionic composition, and the timing of measurement after activation, making it challenging to obtain consistent and reproducible measurements. Here, we present a standardized protocol for assessing sperm motility in Japanese medaka (Oryzias latipes) using a sperm motility analysis system (SMAS), an application for computer-aided sperm motility analysis (CASA). This protocol details the procedures for sperm collection, activation, and quantitative motility assessment, with particular focus on changes in the percentage of motile sperm post activation and the effects of sperm cryopreservation. We demonstrate time-dependent declines in sperm motility and velocity, and highlight the importance of early post-activation measurements to accurately capture peak motility. Notably, cryopreservation significantly accelerated the decline in sperm motility rate without affecting the initial proportion of motile sperm. To enable reliable comparisons among experimental groups, we recommend standardizing the initiation time after sperm activation by using CASA, and show that measurements should be initiated within 1 min after activation to obtain consistent and reliable data. This standardized SMAS-based protocol provides a robust and reproducible framework for sperm motility analysis in medaka and will be valuable not only for studies in reproductive biology, toxicology, and environmental risk assessment but also for applied research, such as breeding of aquacultural fishes.
Three-dimensional (3D) genome organization is dynamically restructured during early vertebrate development, yet how chromatin domains are established remains poorly understood. In particular, the contribution of individual cohesin regulators to this process during embryogenesis is unclear. PDS5 proteins are key modulators of cohesin dynamics, but their depletion has been reported to cause context-dependent and sometimes contrasting architectural effects in cultured cells. Here, we investigated the roles of the cohesin regulators Pds5a and Pds5b during early development using the medaka embryo. Developmental transcriptome analysis revealed distinct but overlapping expression dynamics of pds5a and pds5b around the transition from zygotic genome activation to gastrulation. Morpholino-mediated depletion of either paralog resulted in only mild morphological phenotypes, whereas simultaneous depletion caused more severe developmental defects. In situ Hi-C analysis showed that single depletion of pds5a or pds5b induced only modest changes in 3D genome organization. In contrast, double depletion led to pronounced architectural alterations, including increased long-range chromatin contacts and de novo formation of extended chromatin loops. Transcriptome analysis revealed largely shared, with some condition-specific, gene expression changes in both single- and double-knockdown embryos, indicating that transcriptional effects can occur even in the absence of major architectural disruption. Together, our findings demonstrate that Pds5a and Pds5b act cooperatively to constrain cohesin-mediated long-range interactions during embryogenesis and highlight the importance of analyzing cohesin regulator function within a developmental context to understand how 3D genome organization is established in vivo.
Germ cells in zebrafish are specified by a preformation mechanism, unlike in mice. Max (Myc associated factor X) and its associated PRC1.6 (polycomb repressive complex 1.6) act as negative regulators of germ cell- and meiosis-related genes in mice; however, their function in zebrafish remains unknown. Here, we generated max mutants in zebrafish using genome-editing techniques to investigate the role of Max in germ cell development and meiosis. No obvious morphological abnormalities were observed in the mutants up to 4 days post fertilization (dpf), likely due to maternally supplied max mRNAs. However, the mutants failed to form an inflated swim bladder and gradually died after 10 dpf. The number of primordial germ cells (PGCs) did not differ between the max mutant and wild-type larvae up to 12 dpf. In contrast, analysis of protein expression levels of germ cell-related and meiosis-related genes in PGCs at 9 dpf revealed that the levels of Sycp2, Sycp3, and Dmc1 proteins were significantly increased in max mutants, whereas the expression of Ddx4 and Piwil1 remained unchanged. Together, these results suggest that zebrafish Max selectively represses the expression of a subset of meiotic genes in PGCs.
The Joint Meeting of the 77th Japan Society for Cell Biology (JSCB) and the 58th Japan Society of Developmental Biologists (JSDB) was held from July 16 to 18, 2025, in Nagoya, Japan. With the goal of fostering discussion across disciplinary boundaries and envisioning future directions in cell biology, developmental biology, and related areas of life science, the conference featured various presentations over the course of 3 days: plenary lectures by Keiko Torii (University of Texas/HHMI) and Tian Xu (Westlake University), an educational lecture by Masayuki Miura (National Institute for Basic Biology), 404 poster presentations, and 220 oral presentations. Special panel discussions were organized by the conference chairs, titled "Our Mistakes," followed by "This is My Path in Research," which sparked discussions on life science research through the lens of the Nobel Prize, highlighting dreams, hopes, and passion in scientific careers.
