The objective of this study was to histologically record the ontogenetic changes in the stomach and hepatopancreas of two sesarmid species, Episesarma singaporense and E. versicolor, studied from the zoeal stage 1 to the crab stage. Specimens of ovigerous females were collected from a hatchery site and all stages (zoea 1 to crab) were processed using the morphology and histological method through semithin section. The results of histological analysis of the digestive system were largely organized within the body and showed a complex organization. The distinction between cardiac and pyloric stomachs in both species was unclear in the zoeal 1 and 2 stages but became evident in zoeal stages 3 and 4. All stomach structures in the megalopa and crab stages, especially the well-developed lateral teeth in the cardiac stomach, were clearer than they were in the zoeal stages. The same development was observed in the hepatopancreas that was fully developed by the zoeal 3 stage and became more intricately branched and larger in later stages. This development is an indicator of larval and later feeding activity, which provides information for aquaculture of two sesarmid species.
A central question in developmental biology is how organs acquire their final shape. Since a conserved organ might form through distinct steps, even within animals belonging to the same class, comparative studies are needed to reveal conserved or unique principles. Sea stars are a useful system to investigate how organs develop their specific structure across various species. This species-rich and diverse class of animals provide embryos that can be easily cultured in large numbers and are optically clear, which allows morphogenesis to be observed live. All sea star larvae develop a coelom: a hollow tube that fills the body cavity. We recently named it the “hydro-vascular organ” (HVO), as most of this organ will form the adult water-vascular system after metamorphosis. Understanding the distinct steps that drive HVO development across species requires comparative studies, but detailed characterizations of embryonic and larval stages have been reported for only a few representatives of asteroidea. Here we use brightfield microscopy and live imaging to document for the first time the development of Asterias forbesi, an ecologically important species that lacks a detailed description of embryonic and larval stages. Leveraging the optical clarity of these larvae, we defined distinct stages of HVO morphogenesis. To understand whether the same organ forms through shared steps across different species, we compare A. forbesi HVO development with sea stars from two other orders, Patiria minata and Astropecten aranciacus.
In spiralians, the relationship between early cleavage patterns and the establishment of the juvenile body plan remains one of the central questions. In the oligochaete Tubifex tubifex, the micromeres other than 2d and 4d are bilaterally symmetrically arranged in an arc-shaped assemblage that surrounds the anterior side of the large 2d micromere. The bilateral configuration of the micromeres in Tubifex is distinct from the radially symmetric micromere arrangement in other spiralians. To address the possibility that the bilaterally symmetric arrangement of the micromeres contributes to establishing bilateral symmetry in Tubifex embryos, we mapped micromere fate using DiI as a lineage tracer. The developmental fates of all the micromeres except 2b, 2d, 3b, and 4d were examined. The results showed that the micromeres in T. tubifex embryos lineage-specifically contribute to the head epidermis, cerebral ganglion, buccal cavity, pharynx, oesophagus, and yolk sac ectoderm, comprising the dorsal temporary epithelium and ventral/ventrolateral epidermis, of the juvenile. The micromeres, except for 1c, 1d, and 2c, contributed to a single structure (tissue or organ) of the juvenile. T. tubifex shares most of these micromere-specific structures with other annelids, such as Helobdella, Capitella, and Platynereis. There are two exceptions. One is the temporary epithelium derived from 1c and 1d, which is clitellate-specific; the other is the ventral epidermis derived from 3c and 3d, which is species-specific. The present results showed that the micromeres located to the left of the midline at the 22-cell stage generate the left side of the embryo in terms of tissues and organs, and those located to the right of the midline give rise to the right side of the embryo based on the position of individual micromeres relative to the (future) midline. The pattern of micromere contribution to the left and right sides of the Tubifex embryo is almost identical to that in other spiralians. These results imply that in T. tubifex, the bilateral juvenile body plan is set up by the early cleavage pattern.
The homeobox gene engrailed is a multifunctional regulator with diverse developmental roles across Bilateria, ranging from epithelial boundary formation and neural regionalization to lineage-specific innovations such as arthropod segmentation and molluscan shell-field patterning. Despite this broad functional repertoire, its deployment within Gnathifera has remained largely unknown. Here, I characterize the genomic architecture, protein structure, orthology, and embryonic expression of the single engrailed gene in the monogonont rotifer Brachionus manjavacas. Phylogenetic analyses recover the sequence within the protostome engrailed clade, confirming its orthology. The gene retains the full canonical bilaterian motif complement, including EH1, EH2, the homeodomain (EH4), and the C-terminal EH5 region, and exhibits an intron within EH2 whose position and phase are invariant across protostomes and deuterostomes, indicating deep evolutionary conservation despite extreme variation in intron length among taxa. Embryonic in situ hybridization and immunofluorescence staining reveal a distinctly noncanonical expression pattern. Instead of segmental or ectodermal boundary stripes, engrailed is localized to the protonephridial terminal organs, canal cells, and Huxley’s anastomose (a characteristic interconnection within the protonephridial canal system), and appears transiently in two neurons of the developing foot. These domains display epithelial, ciliary, and neural characteristics, consistent with multifunctional cell identities typical of rotifers. Comparative analysis across Metazoa shows that engrailed expression broadly converges on epithelial and neural boundary contexts, suggesting that such local boundary-type functions may represent the ancestral deployment of the gene. Together, these findings broaden the known developmental repertoire of engrailed and highlight the value of rotifers for comparative studies of bilaterian gene function.
Sex determination, involving the physiological and morphological separation of male and female gamete-producing structures, promotes outcrossing and helps maintain genetic diversity in land plants. In homosporous ferns, which lack sex chromosomes, sex determination is specified during the gametophyte stage and is regulated by intergametophytic signaling mediated by the pheromone antheridiogen. Ceratopteris richardii has long served as a model for dissecting the molecular and cellular mechanisms underlying fern sex determination and associated meristem development in fern gametophytes, and in recent years, important new progress has been achieved. In this review, we summarize recent findings that uncover key environmental and molecular factors influencing antheridiogen responses and highlight the cellular basis of sex-type specification and the initiation and maintenance of meristems in Ceratopteris gametophytes. We also discuss emerging directions in the field, emphasizing the importance of spatial expression dynamics and interacting regulatory networks in fern sexual differentiation. Future advances will likely be driven by integrating genetic tools, multi-omics platforms, and quantitative live-imaging approaches, offering a more comprehensive view of the regulatory logic underlying sex determination and meristem development in ferns.
Evolution and development of the arthropod head are heavily debated topics often referred to as “The arthropod head problem” (AHP) or the “Endless dispute”. One aspect of the AHP concerns the evolutionary origin and homology of the most anterior head segments, the pre-gnathal segments (PGS), that are associated with the tripartite brain of arthropods. It has been suggested that the PGS could have evolved independently from the segments that build the rest of the arthropod body. One argument supporting this hypothesis is that the PGS are patterned by an initial transverse stripe of hedgehog (hh)-expression that splits once or twice, giving (in the case of double splitting) raise to the three PGS in distantly related arthropods such as the fly Drosophila melanogaster and the spider Parasteatoda tepidariorum. It has been implied that this splitting-event may recapitulate evolution of these segments, i.e. the splitting of an initial anterior body unit into three, or at least that the single splitting may represent a remnant of this process. In this paper, I show that two-fold splitting of an initial anterior hh-stripe is not conserved in chelicerates or even spiders. Instead, I find that a single splitting event correlated to the development of the most anterior two segments, the protocerebral and the deuterocerebral segment, is conserved among arthropods as a whole. There are, however, deviations from this pattern including a third or even fourth consecutive head segment, or even hh-splitting in more posterior segments.
β-Catenin has two major functions conserved across metazoans. It enables the interaction of classical cadherin with actin and it is the main transcription factor activated by the canonical Wnt pathway. In these two functions, it acts in patterning of the major body axis in early embroys, in cell differentiation and proliferation. In flatworms, four β-catenin homologs have been identified in the planarian Schmidtea mediterranea. Functional studies revealed that only Smed-β-catenin1 can transduce the Wnt signal and plays a part in defining posterior identity. We made a phylogenetic reconstruction of β-catenin homologs retrieved from a wide range of flatworms and analysed the role of β-catenin during regeneration in Macrostomum lignano. We identified at least two copies of β-catenin in all major taxa except in Catenulida; this suggests that duplication of β-catenin occurred ancestrally in Rhabditophora. In M. lignano, we detected 3 β-catenin homologs. Upon knockdown of the 3 homologs, only Mlig-β-catenin1 blocked blastema formation and regeneration of a tail. After knockdown, posterior regenerates restored normal tails but with instances of imperfect or duplicated tails. Different to planarians, knockdown of Mlig-β-catenins individually or in combination failed to rescue a head in all amputation levels in anterior regenerates. Together, these findings suggest that β-catenin1 is responsible for posterior identity specification also in M. lignano. Our study demonstrates that the ability to rescue a head upon knockdown of β-catenin1 may be an apomorphy of planarians, but is not an ancestral character in flatworms.
Wilhelm Roux promoted the newly emerged field of developmental mechanics by establishing the journal ‘Archiv für Entwicklungsmechanik’, currently known as ‘Development, Genes and Evolution’. The founder and supporters of the journal were all men, as were the authors in the first 3 years of the journal’s existence. We therefore addressed the question—in what ways did women scientists contribute to this new research field and what impact did they have. By investigating the careers and research environment of women authors in the first 50 years of the journal, we show that women contributed to all research areas of developmental mechanics and shaped its future direction.
The chromodomain helicase DNA binding domain 2 (CHD2) gene is an ATPase and a member of the SNF2-like family of helicase-related enzymes. CHD2 plays critical roles in human brain development and function, and homozygous mutation of Chd2 in mice results in perinatal lethality. To further elucidate the effects of chd2, we used CRISPR/Cas9 to create two chd2-knockout strains (fdu901, 11,979-11982delGGGT, and fdu902, 27350delG) in zebrafish. We found that the deformity and mortality rates of fdu901 and fdu902 were higher than those of the wild type. Developmental delay was more obvious and embryo mortality was higher in fdu901 than in fdu902. However, the embryo deformity rate in fdu902 was higher than that in fdu901. Although there were no significant differences in behavior between the two knockout zebrafish and wild-type zebrafish at 7 days post fertilization (dpf), fdu901 and fdu902 zebrafish showed different alterations. The excitability of fdu902 was higher than that of fdu901. Overall, our data demonstrate that two homozygous chd2 knockout mutations were survivable and could be stably inherited and that fdu901 and fdu902 zebrafish differed in behavior and morphology. These two models might be good tools for understanding the functions of the different domains of chd2.
Organisms display a remarkable diversity in their shapes. Although substantial progress has been made in unraveling the mechanisms that govern cell fate determination during development, the mechanisms by which fate-determined cells give rise to the final shapes of organisms remain largely unknown. This study describes in detail the process of the final shape formation of the tarsus, which is near the distal tip of the adult leg, during the pupal stage in Drosophila melanogaster. Days-long live imaging revealed unexpectedly complicated cellular dynamics. The epithelial cells transiently form the intriguing structure, which we named the Parthenon-like structure. The basal surface of the epithelial cells and localization of the basement membrane protein initially show a mesh-like structure and rapidly shrink into the membranous structure during the formation and disappearance of the Parthenon-like structure. Furthermore, macrophage-like cells are observed moving around actively in the Parthenon-like structure and engulfing epithelial cells. The findings in this research are expected to significantly contribute to our understanding of the mechanisms involved in shaping the final structure of the adult tarsus.
Folsomia candida is a tiny soil-living arthropod belonging to the Collembola, which is an outgroup to Insecta. It resembles insects as having a pair of antennae and three pairs of thorax legs, while it also possesses three abdominal appendages: a ventral tube located in the first abdominal segment (A1), a retinaculum in A3, and a furca in A4. Collembolan Ubx and AbdA specify abdominal appendages, but they are unable to repress appendage marker gene Dll. The genetic basis of collembolan appendage formation and the mechanisms by which Ubx and AbdA regulate Dll transcription and appendage development remains unknown. In this study, we analysed the developmental transcriptomes of F. candida and identified candidate appendage formation genes, including Ubx (FcUbx). The expression data revealed the dominance of Dll over Ubx during the embryonic 3.5 and 4.5 days, suggesting that Ubx is deficient in suppressing Dll at early appendage formation stages. Furthermore, via electrophoretic mobility shift assays and dual luciferase assays, we found that the binding and repression capacity of FcUbx on Drosophila Dll resembles those of the longest isoform of Drosophila Ubx (DmUbx_Ib), while the regulatory mechanism of the C-terminus of FcUbx on Dll repression is similar to that of the crustacean Artemia franciscana Ubx (AfUbx), demonstrating that the function of collembolan Ubx is intermediate between that of Insecta and Crustacea. In summary, our study provides novel insights into collembolan appendage formation and sheds light on the functional evolution of Ubx. Additionally, we propose a model that collembolan Ubx regulates abdominal segments in a context-specific manner.
The zebrafish is an invaluable model organism for genetic, developmental, and disease research. Although its high conservation with humans is often cited as justification for its use, the zebrafish harbors oft-ignored genetic characteristics that may provide unique insights into gene structure and function. Zebrafish, along with other teleost fish, underwent an additional round of whole genome duplication after their split from tetrapods—resulting in an abundance of duplicated genes when compared to other vertebrates. These duplicated genes have evolved in distinct ways over the ensuing 350 million years. Thus, each gene within a duplicated gene pair has nuanced differences that create a unique identity. By investigating both members of the gene pair together, we can elucidate the mechanisms that underly protein structure and function and drive the complex interplay within biological systems, such as signal transduction cascades, genetic regulatory networks, and evolution of tissue and organ function. It is crucial to leverage such studies to explore these molecular dynamics, which could have far-reaching implications for both basic science and therapeutic development. Here, we will review the role of gene duplications and the existing models for gene divergence and retention following these events. We will also highlight examples within each of these models where studies comparing duplicated genes in the zebrafish have yielded key insights into protein structure, function, and regulation.
The antennal flagellum of the locust S. gregaria is an articulated structure bearing a spectrum of sensilla that responds to sensory stimuli. In this study, we focus on the basiconic-type bristles as a model for sensory system development in the antenna. At the end of embryogenesis, these bristles are found at fixed locations and then on only the most distal six articulations of the antenna. They are innervated by a dendrite from a sensory cell cluster in the underlying epithelium, with each cluster directing fused axons topographically to an antennal tract running to the brain. We employ confocal imaging and immunolabeling to (a) identify mitotically active sense organ precursors for sensory cell clusters in the most distal annuli of the early embryonic antenna; (b) observe the subsequent spatial appearance of their neuronal progeny; and (c) map the spatial and temporal organization of axon projections from such clusters into the antennal tracts. We show that early in embryogenesis, proliferative precursors are localized circumferentially within discrete epithelial domains of the flagellum. Progeny first appear distally at the antennal tip and then sequentially in a proximal direction so that sensory neuron populations are distributed in an age-dependent manner along the antenna. Autotracing reveals that axon fasciculation with a tract is also sequential and reflects the location and age of the cell cluster along the most distal annuli. Cell cluster location and bristle location are therefore represented topographically and temporally within the axon profile of the tract and its projection to the brain.
Bilateria encompass the vast majority of the animal phyla. As the name states, they are bilaterally symmetric, that is with a morphologically clear main body axis connecting their anterior and posterior ends, a second axis running between their dorsal and ventral surfaces, and with a left side being roughly a mirror image of their right side. Bone morphogenetic protein (BMP) signalling has widely conserved functions in the formation and patterning of the second, dorso-ventral (DV) body axis, albeit to different extents in different bilaterian species. Whilst initial findings in the fruit fly Drosophila and the frog Xenopus highlighted similarities amongst these evolutionarily very distant species, more recent analyses featuring other models revealed considerable diversity in the mechanisms underlying dorsoventral patterning. In fact, as phylogenetic sampling becomes broader, we find that this axis patterning system is so evolvable that even its core components can be deployed differently or lost in different model organisms. In this review, we will try to highlight the diversity of ways by which BMP signalling controls bilaterality in different animals, some of which do not belong to Bilateria. Future research combining functional analyses and modelling is bound to give us some understanding as to where the limits to the extent of the evolvability of BMP-dependent axial patterning may lie.
Dmrt (doublesex and mab-3 related transcription factor) is a protein family of transcription factors implicated in sexual regulation. Dmrt proteins are widely conserved and known for their involvement in sex determination and differentiation across species, from invertebrates to humans. In this study, we identified a novel gene with a DM (doublesex/Mab-3)-domain gene in the river prawn, Macrobrachium nipponense, which we named MniDmrt1B due to its similarities and close phylogenetic relationship with Dmrt1B in Macrobrachium rosenbergii. Through amino acid alignments and structural predictions, we observed conservation and identified putative active sites within the DM domain. qRT-PCR analysis revealed that MniDmrt1B exhibited high expression levels in the testis, with consistently higher expression in males compared to females during development. Additionally, similar to other sex-regulated genes, the MniDmrt1B gene exhibited high expression levels during the sex differentiation-sensitive periods in M. nipponense. These results strongly indicated that MniDmrt1B probably plays an important role in testis development and sex differentiation in M. nipponense.
Most of annelids grow all over their asexual life through the continuous addition of segments from a special zone called “segment addition zone” (SAZ) adjacent to the posterior extremity called pygidium. Amputation of posterior segments leads to regeneration (posterior regeneration-PR) of the pygidium and a new SAZ, as well as new segments issued from this new SAZ. Amputation of anterior segments leads some species to regeneration (anterior regeneration-AR) of the prostomium and a SAZ which produces new segments postero-anteriorly as during PR. During the 1960s and 1970s decades, experimental methods on different species (Syllidae, Nereidae, Aricidae) showed that the function of SAZ depends on the presence and number of mesodermal regeneration cells. Selective destruction of mesodermal regeneration cells in AR had no effect on the regeneration of the prostomium, but as for PR, it inhibited segment regeneration. Thus, worms deprived of mesodermal regeneration cells are always able to regenerate the pygidium or the prostomium, but they are unable to regenerate segments, a result which indicates that the SAZ functions only if these regeneration cells are present during PR or AR. Additionally, during AR, nerve fibres regenerate from the cut nerve cord toward the newformed brain, a situation which deprives the SAZ of local regenerating nerve fibres and their secreted growth factors. In contrast, during PR, nerve fibres regenerate both during the entire regeneration phase and then in normal growth. This review summarizes the experimental evidence for mesoderm cell involvement in segment regeneration, and the differential impact of the digestive tube and the regenerated nerve cord during PR vs AR.
AF4/FMR2 family member (AFF) proteins are a group of transcriptional regulators that can regulate gene transcription and play an important role in cellular physiological processes such as proliferation and differentiation. The transcriptome data of the lamprey spinal cord injury were analyzed in previous research. We then identified a hub gene, Lr-AFF3, from this dataset. Phylogenetic tree analysis determined the evolutionary relationships of the AFF gene family across different species. In addition, analysis of motifs, domains, and 3D structures further confirmed the conservatism of the AFF gene family. In particular, the gene structure of the AFF3 gene was not conserved, possibly because of intron insertion. It was also found that the neighboring genes of the Lr-AFF3 gene had a higher diversity than that in jawed vertebrates through synteny analysis. The results of the MTT and EdU experiments showed that the C-terminal homology domain (CHD) and N-terminal homology domain (NHD) of Lr-AFF3 promoted cell proliferation. In summary, our research will not only provide new insights into the origin and evolution of the AFF gene family in different species, but also provide new clues for the functions of Lr_AFF3.
The family Tephritidae comprises numerous fruit fly species, some of which are economically significant, such as several in the genus Anastrepha. Most pest species in this genus belong to the fraterculus group, characterized by closely related species that are difficult to differentiate due to recent divergence and gene flow. Identifying genetic markers for their study is paramount for understanding the group’s evolution and eventual phytosanitary control. Because there is variation in eggshell morphology among species in the genus, the study of the rapidly evolving defective chorion 1 (dec-1) gene, which is crucial for chorion formation and reproduction, could provide relevant information for Anastrepha differentiation. We compared transcriptome sequences of dec-1 from two of the most important pest species in the genus, Anastrepha fraterculus and Anastrepha obliqua to dec-1 sequences from Anastrepha ludens, which was used for structure prediction. Furthermore, we amplified a conserved exon across populations of these species. These data revealed three alternative transcripts in A. fraterculus and A. obliqua, consistent with patterns found in other Tephritidae; we obtained orthologous sequences for these other tephritids from NCBI to investigate patterns of selection affecting this gene at different hierarchical levels using different methods. These analyses show a general pattern of purifying selection across the whole gene and throughout its history at different hierarchical levels, from populations to more distantly related species. That notwithstanding, we still found evidence of positive and episodic diversifying selection at different levels. Different parts of the gene have shown distinct evolutionary rates, which were associated with the diverse proproteins produced by posttranslational changes of DEC-1, with proproteins that are incorporated in the chorion earlier in egg formation being in general more conserved than others that are incorporated later. This correlation appears more evident in certain lineages, including the branch that separates Anastrepha, as well as other internal branches that differentiate species within the genus. Our data showed that this gene shows remarkable variation across its different exons, which has proven to be informative at different evolutionary levels. These changes hold promise not only for studying differentiation in Anastrepha but also for the eventual management of selected pest species.
One hurdle in the development of zebrafish models of human disease is the presence of multiple zebrafish orthologs resulting from whole genome duplication in teleosts. Mutations in inositol polyphosphate 5-phosphatase K (INPP5K) lead to a syndrome characterized by variable presentation of intellectual disability, brain abnormalities, cataracts, muscle disease, and short stature. INPP5K is a phosphatase acting at position 5 of phosphoinositides to control their homeostasis and is involved in insulin signaling, cytoskeletal regulation, and protein trafficking. Previously, our group and others have replicated the human phenotypes in zebrafish knockdown models by targeting both INPP5K orthologs inpp5ka and inpp5kb. Here, we show that inpp5ka is the more closely related orthologue to human INPP5K. While both inpp5ka and inpp5kb mRNA expression levels follow a similar trend in the developing head, eyes, and tail, inpp5ka is much more abundantly expressed in these tissues than inpp5kb. In situ hybridization revealed a similar trend, also showing unique localization of inpp5kb in the pineal gland and retina indicating different transcriptional regulation. We also found that inpp5kb has lost its catalytic activity against its preferred substrate, PtdIns(4,5)P2. Since most human mutations are missense changes disrupting phosphatase activity, we propose that loss of inpp5ka alone can be targeted to recapitulate the human presentation. In addition, we show that the function of inpp5kb has diverged from inpp5ka and may play a novel role in the zebrafish.
Current sequencing technology allows for the relatively affordable generation of highly contiguous genomes. Technological advances have made it possible for researchers to investigate the consequences of diverse sorts of genomic variants, such as gene gain and loss. With the extraordinary number of high-quality genomes now available, we take stock of how these genomic variants impact phenotypic evolution. We take care to point out that the identification of genomic variants of interest is only the first step in understanding their impact. Painstaking lab or fieldwork is still required to establish causal relationships between genomic variants and phenotypic evolution. We focus mostly on arthropod research, as this phylum has an impressive degree of phenotypic diversity and is also the subject of much evolutionary genetics research. This article is intended to both highlight recent advances in the field and also to be a primer for learning about evolutionary genetics and genomics.
