Biology subjects

Masai, I.

Publications and source records attributed to Masai, I..

7 recordsLinked to original sources

bioRxiv2023

Fibroblast Growth Factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac

The spheroidal shape of the eye lens is critical for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating lamellipodium is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin, and actin reduced the height of both early and later fibers, indicating elongation of these fibers relies on actomyosin contractility. Consistently, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose it to do so through regulation of Rho activity. Summary statementFGF differentially regulates Rho- and Rac-activity at the lens equator to promote lens fiber cell elongation and migration.

developmental biology↗

bioRxiv2023

Dynamics of dominance: maneuvers, contests, and assessment in the posture-scalemovements of interacting zebrafish

While two-body fighting behavior occurs throughout the animal kingdom to settle dominance disputes, important questions such as how the dynamics ultimately lead to a winner and loser are unresolved. Here we examine fighting behavior at high-resolution in male zebrafish. We combine multiple cameras, a large volume containing a transparent interior cage to avoid reflection artifacts, with computer vision to track multiple body points across multiple organisms while maintaining individual identity in 3D. In the body point trajectories we find a spectrum of timescales which we use to build informative joint coordinates consisting of relative orientation and distance. We use the distribution of these coordinates to automatically identify fight epochs, and we demonstrate the post-fight emergence of an abrupt asymmetry in relative orientations-a clear and quantitative signal of hierarchy formation. We identify short-time, multi-animal behaviors as clustered transitions between joint configurations, and show that fight epochs are spanned by a subset of these clusters, which we denote as maneuvers. The resulting space of maneuvers is rich but interpretable, including motifs such as "attacks" and "circling". In the longer-time dynamics of maneuver frequencies we find differential and changing strategies, including that the eventual loser attacks more often towards the end of the contest. Our results suggest a reevaluation of relevant assessment models in zebrafish, while our approach is generally applicable to other animal systems.

biophysics↗

bioRxiv2023

Male germ cell-associated kinase (MAK) is required for axoneme formation during ciliogenesis in zebrafish photoreceptors

Vertebrate photoreceptors are highly specialized retinal neurons that have cilium-derived membrane organelles called outer segments (OS), which function as platforms for phototransduction. Male germ cell-associated kinase (MAK) is a cilium-associated serine/threonine kinase, and its genetic mutation causes photoreceptor degeneration in mice and retinitis pigmentosa in humans. However, the role of MAK in photoreceptors is not fully understood. Here, we report that zebrafish mak mutants show rapid photoreceptor degeneration during embryonic development. In mak mutants, both cone and rod photoreceptors completely lack OSs and undergo apoptosis. Interestingly, zebrafish mak mutants fail to generate axonemes during photoreceptor ciliogenesis, whereas basal bodies are specified. These data suggest that MAK contributes to axoneme development in zebrafish, in contrast to mouse Mak mutants, which have elongated photoreceptor axonemes. Furthermore, the kinase activity of MAK is critical in ciliary axoneme development and photoreceptor survival. Thus, MAK is required for ciliogenesis and OS formation in zebrafish photoreceptors to ensure intracellular protein transport and photoreceptor survival. Summary statementMale germ cell-associated kinase (MAK) is a cilium-associated serine/threonine kinase that promotes axoneme development during ciliogenesis in zebrafish photoreceptors to ensure intracellular protein transport and photoreceptor survival.

cell biology↗

bioRxiv2022

Single-cell transcriptome analysis reveals heterogeneity and a dynamic regenerative response of quiescent radial glia in adult zebrafish brain

In zebrafish telencephalon, radial glial cells (RGs) show a remarkable ability to regenerate damaged neural tissue by re-initiating cell proliferation to produce neural precursors to rebuild the lost neural circuit. However, it is not fully understood how RGs respond to brain damage to initiate this regenerative response. Here we applied single-cell transcriptomics to RGs in adult zebrafish telencephalon and identified five RG subtypes, which are classified into four quiescent RGs (qRGs) and one proliferating RG (pRG). The four qRGs differentially express distinct subsets of qRG markers, suggesting heterogeneity of qRG in zebrafish adult brain. Interestingly, one qRG subtype shows high expression of ribosomal proteins, and its fraction increases in response to brain damage. Consistently, the mTOR pathway is activated in RGs near the injury site. It was reported that inflammatory responses of brain-resident immune cells, microglia, are required for inducing regenerative responses of RGs in zebrafish. Genetical elimination of microglia not only suppressed the damage-induced regenerative response of RGs, but also decreased the fraction of the ribosomal expression-enriched qRGs. Our pseudo-time analysis suggests that putative dormant RGs produce ribosomal expression-enriched qRGs through activation of ribosomal genesis, as well as suppression of cholesterol biogenesis, and pRGs through activation of the JAK/STAT pathway. Our findings reveal heterogeneity of qRGs in adult zebrafish brain and their dynamic regenerative response to brain damage.

neuroscience↗

bioRxiv2021

Banp regulates DNA damage response and chromosome segregation during the cell cycle in zebrafish retina

Btg3-associated nuclear protein (Banp) was originally identified as a nuclear matrix-associated region (MAR)-binding protein and it functions as a tumor suppressor. At the molecular level, Banp regulates transcription of metabolic genes via a CGCG-containing motif called the Banp motif. However, its physiological roles in embryonic development are unknown. Here we report that Banp is indispensable for the DNA damage response and chromosome segregation during mitosis. Zebrafish banp mutants show mitotic cell accumulation and apoptosis in developing retina. We found that DNA replication stress and tp53-dependent DNA damage responses were activated to induce apoptosis in banp mutants, suggesting that Banp is required for regulation of DNA replication and DNA damage repair. Furthermore, consistent with mitotic cell accumulation, chromosome segregation was not smoothly processed from prometaphase to anaphase in banp morphants, leading to a prolonged M-phase. Our RNA- and ATAC-sequencing identified 31 candidates for direct Banp target genes that carry the Banp motif. Interestingly, a DNA replication fork regulator, wrnip1, and two chromosome segregation regulators, cenpt and ncapg, are included in this list. Thus, Banp directly regulates transcription of wrnip1 for recovery from DNA replication stress, and cenpt and ncapg for chromosome segregation during mitosis. Our findings provide the first in vivo evidence that Banp is required for cell-cycle progression and cell survival by regulating DNA damage responses and chromosome segregation during mitosis.

cell biology↗

bioRxiv2021

Strip1 regulates retinal ganglion cell survival by suppressing Jun-mediated apoptosis to promote retinal neural circuit formation

In the vertebrate retina, an interplay between retinal ganglion cells (RGCs), amacrine, and bipolar cells establishes a synaptic layer called the inner plexiform layer (IPL). This circuit conveys signals from photoreceptors to visual centers in the brain. However, the molecular mechanisms involved in its development remain poorly understood. Striatin-interacting protein 1 (Strip1) is a core component of the STRIPAK complex, and it has shown emerging roles in embryonic morphogenesis. Here, we uncover the importance of Strip1 in inner retina development. Using zebrafish, we show that loss of Strip1 causes defects in IPL formation. In strip1 mutants, RGCs undergo dramatic cell death shortly after birth. Amacrine and bipolar cells subsequently invade the degenerating RGC layer, leading to a disorganized IPL. Mechanistically, zebrafish Strip1 interacts with its STRIPAK partner, Striatin3, and both show overlapping functions in RGC survival. Furthermore, loss of Strip1 or Striatin 3, leads to activation of the pro-apoptotic marker, Jun, within RGCs, and Jun knockdown rescues RGC survival in strip1 mutants. In addition to its function in RGC maintenance, Strip1 is required for RGC dendritic patterning, which likely contributes to proper IPL formation. Taken together, we propose that a series of Strip1-mediated regulatory events coordinates inner retinal circuit formation by maintaining RGCs during development, which ensures proper positioning and neurite patterning of inner retinal neurons.

developmental biology↗

bioRxiv2021

Mechanisms underlying microglial colonization of developing neural retina in zebrafish

Microglia are brain-resident macrophages that function as the first line of defense in brain. Embryonic microglial precursors originate in peripheral mesoderm and migrate into the brain during development. However, the mechanism by which they colonize the brain is incompletely understood. The retina is one of the first brain regions to accommodate microglia. In zebrafish, embryonic microglial precursors use intraocular hyaloid blood vessels as a pathway to migrate into the optic cup via the choroid fissure. Once retinal progenitor cells exit the cell cycle, microglial precursors associated with hyaloid blood vessels start to infiltrate the retina preferentially through neurogenic regions, suggesting that colonization of retinal tissue depends upon the neurogenic state. Along with blood vessels and retinal neurogenesis, IL34 also participates in microglial precursor colonization of the retina. Altogether, CSF receptor signaling, blood vessels, and neuronal differentiation function as cues to create an essential path for microglial migration into developing retina.

developmental biology↗