Biology subjects

Maeno, A.

Publications and source records attributed to Maeno, A..

7 recordsLinked to original sources

bioRxiv2026

Extensive loss of HoxA/D genes does not disrupt anterior vertebral patterning in zebrafish

Hox genes play central roles in specifying positional identities along the vertebrate anterior-posterior axis. In mice, genetic analyses have demonstrated that Hox genes distributed among the four Hox clusters contribute to vertebral patterning, with extensive functional redundancy among paralogous genes. Our previous genetic analysis in zebrafish identified important roles for HoxB- and HoxC-related genes in specifying anterior vertebral identities, whereas the contributions of HoxA- and HoxD-related genes remained unresolved. Here, we examined adult zebrafish carrying extensive combinations of hoxaa, hoxab, and hoxda cluster deletions and generated five-gene homozygous mutants carrying frameshift mutations in hoxa3a, hoxa4a, hoxa5a, hoxd3a, and hoxd4a. X-ray micro-CT analysis revealed no obvious alterations in anterior vertebral morphology in either the compound cluster mutants or the five-gene mutants. These results indicate that HoxA/D genes make only a limited detectable contribution to anterior vertebral patterning in zebrafish. Together with our previous findings, they suggest that vertebral patterning functions are distributed unevenly among zebrafish Hox clusters, with a predominant contribution from HoxB/C-related genes.

developmental biology↗

bioRxiv2025

The phenotypic variation of widefins medaka is due to the insertion of a giant transposon containing a viral genome within hoxca cluster

Phenotypic variation in species arises from genetic differences and environmental influences on gene expression. Differences in epigenetic modifications, such as histone modifications and DNA methylation, can also contribute to phenotypic variations, even among individuals with identical genetic information. However, the underlying molecular mechanisms are not yet fully understood, particularly in vertebrates. The number of fin rays in teleosts, such as medaka, serves as a useful model for studying this variation. In a previous study, we demonstrated that the teleost Hox code plays a crucial role in determining the anterior-posterior identity necessary for the formation of dorsal and anal fins. In this study, we investigated widefins medaka, a spontaneous mutant displaying phenotypic variation in the number of dorsal and anal fin rays. Long-read whole-genome sequencing revealed that an extremely large transposon, Teratorn, containing a herpesvirus genome, was inserted into the hoxc12a 3 UTR. This insertion decreased hoxc12a expression and, in some cases, also affected neighboring hox genes, resulting in variations in fin size and the presence or absence of dorsal fins. Additionally, hoxc6a, located 50 kb away from the insertion, was also downregulated in widefins medaka. These findings suggest that this large transposon insertion leads to a reduction in nearby hox gene expression, contributing to the phenotypic variation observed in widefins medaka. These results highlight the role of transposable elements and epigenetic regulation in generating phenotypic diversity in vertebrates.

genetics↗

bioRxiv2024

Physical constraints on the positions and dimensions of the zebrafish swim bladder by surrounding bones

Precise regulation of organ size and position is crucial for optimal organ function. Since the swim bladder is primarily responsible for buoyancy in teleosts, early development and subsequent inflation of the swim bladder should be appropriately controlled with the body growth. However, the underlying mechanism remains unclear. In this study, we show that the size and position of the swim bladder are physically constrained by the surrounding bones in zebrafish. Non-invasive micro-CT scanning revealed that the anterior edge of the swim bladder is largely attached to the os suspensorium, which is an ossicle extending medioventrally from the 4th vertebra. Additionally, we observed that hoxc6a mutants, which lack the os suspensorium, exhibited an anterior projection of the swim bladder beyond the 4th vertebra. During the swim bladder development, we found that the counterclockwise rotation of the os suspensorium correlates with posterior regression of the swim bladder, suggesting that the os suspensorium pushes the swim bladder posteriorly into its proper position. Furthermore, our results revealed a close association between the posterior region of the swim bladder and the pleural ribs. In hoxaa cluster mutants with additional ribs, the swim bladder expanded posteriorly, accompanied by an enlarged body cavity. Taken together, our results demonstrate the importance of the surrounding bones in the robust regulation of swim bladder size and position in zebrafish.

developmental biology↗

bioRxiv2024

The functional roles of zebrafish HoxA- and HoxD-related clusters in the pectoral fin development

The paralogs 9-13 Hox genes in mouse HoxA and HoxD clusters are critical for limb development. When both HoxA and HoxD clusters are deleted in mice, significant limb truncation is observed compared to the phenotypes of single and compound mutants of Hox9-13 genes in these clusters. In zebrafish, mutations in hox13 genes in HoxA- and HoxD-related clusters result in abnormal morphology of pectoral fins, homologous to forelimbs. However, the effect of the simultaneous deletions of entire HoxA- and HoxD-related clusters on pectoral fin development remains unknown. Here, we generated mutants with several combinations of hoxaa, hoxab, and hoxda cluster deletions and analyzed the pectoral fin development. In hoxaa-/-;hoxab-/-;hoxda-/- larvae, the endoskeletal disc and the fin-fold are significantly shortened in developing pectoral fins. In addition, we show that this anomaly is due to defects in the pectoral fin growth after the fin bud formation. Furthermore, in the surviving adult mutants, micro-CT scanning reveals defects in the posterior portion of the pectoral fin which is thought to represent latent regions of the limb. Our results further support that the functional role of HoxA and HoxD clusters is conserved in the paired appendage formation in bony fishes.

developmental biology↗

bioRxiv2023

Leaf- and diverged shoot meristem programs shape the stem in rice

The stem is the shoot axis in seed plants and has been a primary target in breeding to regulate crop height. However, early processes of stem development remain elusive. Here we show that regulators for shoot meristems and leaves determine the node-internode pattern in rice. Mutants of KNOX1 genes OSH15 and OSH1, known to maintain shoot meristem indeterminacy1,2, showed dwarfism due to enlarged nodes and diminished internodes. These genes confine node differentiation by repressing leaf developmental regulator YABBY genes in internodal vasculatures. YABBY expression, which normally extends from leaves to nodes along vasculatures, promotes nodal vascular differentiation and limits stem elongation. It expands in knox1 mutants, and the loss of YABBY genes reverts their dwarfism. OSH15 also represses node-specific KNOX1 subclade genes OSH6 and OSH71 to allow internode elongation. Importantly, both YABBY and node-specific KNOX1 genes are required for pulvinus formation at the leaf base, further elaborating the nodal structure for gravitropism. Thus, intersections between leaf and sub-functionalized shoot meristem programs shape nodes and internodes along the stem. Phylogenetic analysis showed that KNOX1 sub-functionalization likely occurred in the progenitor of gymnosperms and angiosperms. Given that seed plants acquired their leaves independently from other vascular plant lineages3,4, the emergence of the node-internode pattern and KNOX1-YABBY regulatory module may be linked to seed plant leaf evolution.

plant biology↗

bioRxiv2023

Heat-shock inducible clonal analysis reveals the stepwise establishment of cell fates in the rice stem.

The stem, consisting of nodes and internodes, is one of the major organs in seed plants. In contrast to other organs, however, processes of stem development remain elusive, especially when nodes and internodes are initiated. By introducing an intron into the Cre recombinase gene, we established a heat-shock inducible clonal analysis system in a single binary vector and applied it to the stem in the flag leaf phytomer of rice. With detailed characterizations of stem development, we show that cell fate acquisition for each domain of the stem occurs stepwise. Cell fates for a single phytomer and the foot (non-elongating domain at the stem base) were established in the shoot apical meristem by one plastochron before the leaf initiation. The fate acquisition for the node occurred just before the leaf initiation, separating cell lineages for leaves and stems. Subsequently, fates for the axillary bud were established in early leaf primordia. Finally, cells committed to the internode emerged from, at most, a few tiers of cells when the stem epidermis was at the 12[~]25 celled stage. Thus, the internode is the last part of the stem whose cell fate is established. This study provides a groundwork to unveil underlying molecular mechanisms in stem development and a useful tool for clonal analysis, which can be applied to various species.

plant biology↗

bioRxiv2018

doublesex regulates sexually dimorphic beetle horn formation by integrating spatial and temporal developmental contexts in the Japanese rhinoceros beetle Trypoxylus dichotomus

AbstractMany scarab beetles have sexually dimorphic exaggerated horns that are an evolutionary novelty. Since the shape, number, size, and location of horns are highly diverged within Scarabaeidae, beetle horns are an attractive model for studying the evolution of sexually dimorphic and novel traits. In beetles including the Japanese rhinoceros beetle Trypoxylus dichotomus, the sex determination gene doublesex (dsx) plays a crucial role in sexually dimorphic horn formation during larval-pupal development. However, knowledge of when and how dsx drives the gene regulatory network (GRN) for horn formation to form sexually dimorphic horns during development remains elusive. To address this issue, we identified a Trypoxylus-ortholog of the sex determination gene, transformer (tra), that regulates sex-specific splicing of the dsx pre-mRNA, and whose loss of function results in sex transformation. By knocking down tra function at multiple developmental timepoints during larval-pupal development, we estimated the onset when the sex-specific GRN for horn formation is driven. In addition, we also revealed that dsx regulates different aspects of morphogenetic activities during the prepupal and pupal developmental stages to form appropriate morphologies of pupal head and thoracic horn primordia as well as those of adult horns. Based on these findings, we discuss the evolutionary developmental background of sexually dimorphic trait growth in horned beetles.\n\nAuthor Summary:\n\nBeetle horns are highly enriched in a particular family Scarabaeidae, although the shape, size and number of horns are diversified within the group. In addition, many scarab beetle horns are sexually dimorphic. It has been questioned how a particular group of beetles has originated and diversified evolutionary novel horns. Here we found the exact time when morphological sexual dimorphism of horn primordia appeared, estimated the onset of the developmental program for sexually dimorphic horn formation driven by Doublesex, and revealed that Doublesex regulates different aspects of cell activities of horn primordia depending on the spatiotemporal contexts. Our study provides our understanding regarding regulatory shifts in these mechanisms during the evolution of sexually dimorphic traits in horned beetles.

developmental biology↗