Journal of experimental zoology. Part B, Molecular and developmental evolution最新文献

Biomineralization, the formation of mineralized tissues like skeletons and shells, is an essential developmental process in diverged phyla. Vertebrates' biomineralization involves the secretion of specialized extracellular matrix (ECM) proteins and the formation of Integrin-based focal adhesions, yet less is known about the role of such factors in invertebrates. A recent study has shown that focal adhesions form around the calcite spicule of the sea urchin larva, however, the skeletogenic expression and role of adhesion related proteins in this system are understudied. Here, we identified a set of ECM and adhesion genes that show enriched expression in the sea urchin skeletogenic cells and studied the role of the ECM protein, Npnt, in Paracentrotus lividus. The integrin alpha proteins, Pl-Ahi, Pl-Aji, Pl-Api, and the Pl-Talin protein are highly conserved between sea urchin and humans and the expression of these genes is enriched in the skeletogenic cells during early skeletogenesis. Pl-npnt is expressed specifically in skeletogenic cells throughout skeletogenesis and requires Vascular Endothelial Growth Factor (VEGF) signaling for its maintenance. Genetic perturbations of Pl-npnt result in skeletal defects, including reduced length of skeletal rods, ectopic spicule formation and branching, while skeletogenic cell migration remained unaffected. The activation of focal adhesion kinase (FAK) around the spicules is independent of Pl-Npnt activity in agreement with the loss of Integrin binding site in the sea urchin Npnt protein. Our findings set the stage for further analyses of ECM and adhesion-mediated mechanisms that drive sea urchin biomineralization, and most likely participate in skeletal development across metazoans.

Nemertea is a phylum of predominantly marine worms that exhibit various larval forms, including the iconic pilidium. Pelagic lecithotrophic pilidia are considered more derived than pelagic planktotrophic pilidia, but data on the structure of lecithotrophic larvae are limited to the light-optical level. Here, we study the lecithotrophic reversed Iwata's larvae of an undescribed heteronemertean, Nipponomicrura sp. Using transmission electron microscopy and confocal laser scanning microscopy with F-actin, acetylated α-tubulin, and serotonin (5-hydroxytryptamine) labeling, the provisional structures of the larva are described. The larval envelope of Nipponomicrura sp. consists of three layers: the epidermis, the circular musculature, and the epithelium of the amnion. The larval epidermis contains a considerable amount of yolk, only half of which is consumed by the end of metamorphosis. The apical plate consists of 5-hydroxytryptamine-negative cells, each bearing a cilium surrounded by a collar of eight to nine microvilli. Four monociliated 5-hydroxytryptamine-like-immunoreactivity sensory apical neurons are associated with the apical plate. For the first time, a pair of longitudinal muscles running along the body of the juvenile and joining the anterior and posterior parts of the provisional epithelium has been identified in nemertean larvae. These muscles serve as retractors of the apical plate and fix the position of the juvenile within the larva. The obtained data indicate a similar morphology of the apical organ in Pilidiophora larvae; however, in the Nipponomicrura sp. larva, there are more layers under the apical plate, and the muscle-retractor is derived from two longitudinal muscle cords that pass through the juvenile's body, and in posterior pole, attach at the base of the larval envelope.

Cilia are found on the epithelia of almost all metazoans, so their absence from the epithelia of all but one class of Porifera is puzzling. Homoscleromorph sponges possess ciliated epithelia, but their function and evolutionary history within Porifera are unclear. We compared the ciliary beat frequencies (CBFs) of cilia on outer epithelia of the homoscleromorph sponge Oscarella sp. with those of other animals to suggest possible functions for the cilia. Settled Stage 4 buds, or juveniles, were found to have a higher CBF than free-moving Stage 1 buds, and CBF was within the range of cilia that function in mucus transport in other aquatic invertebrates. Scanning Electron Microscopy (SEM) images of buds fixed with ruthenium red to detect the presence of mucus showed that mucus was associated with the cilia of the exopinacoderm and both SEM and immunofluorescence images revealed fields of homogeneously oriented cilia. Confocal imaging of fluorescent beads also showed that cilia beat in the same direction. Movement of beads was reduced by nocodazole treatment indicating that the movement of particles over the surface was caused by ciliary beat. These results suggest that cilia on the epithelia of Homoscleromorph sponges are involved in mucociliary-driven particle flux, and may be used to clean the surface using mucus.

In vertebrates, the provision of nutrients to developing embryos varies widely, ranging from yolk-dependent strategies to highly specialized forms of placental nourishment. Vitellogenins (VTGs) are essential proteins for egg yolk formation in oviparous and lecithotrophic species. In contrast, in eutherian mammals, the loss of VTGs is associated with the evolution of matrotrophy (placentotrophy and lactation), where maternal nutrition via the placenta replaces the need for large yolk reserves during embryonic development. Marisora sp., a placentotrophic viviparous lizard with the most complex placenta known in reptiles, exhibits truncated vitellogenesis, resulting in the production of microlecithal eggs. This study investigated the presence of VTGs in Marisora sp. using RNA-seq from the liver and ovary at previtellogenesis and vitellogenesis stages. No corresponding annotations for VTGs were found. This absence may be associated with the placentotrophic nutrition of the embryo, suggesting modifications in lipid production and transport to the ovarian follicles. Apolipoprotein B (ApoB) and microsomal triglyceride transfer proteins (MTP) were identified, which are closely related to VTGs and could fulfill their function, especially ApoB, which is involved in yolk formation in lecithotrophic species in which VTGs are absent. The absence of VTGs in the Marisora sp. transcriptome represents a key discovery in the evolution of obligate placentotrophic viviparity in reptiles, highlighting convergent traits with mammals. Genomic studies are required to determine if changes in VTG genes prevent or modify their expression, and proteomic studies are needed to fully understand the role of other lipid transport proteins in the preovulatory ovarian follicles of these lizards.

Thyroid hormones (THs) are important regulators of somatic development in vertebrates. In anurans, they control critical processes such as early limb differentiation, tail resorption, and tissue and organ restructuring, enabling the transition from aquatic larvae to terrestrial adults. However, their role in gonadal development remains less understood, particularly as gonadal differentiation often occurs independently of larval growth and metamorphic remodeling. In this study, we analyzed the morphogenesis of gonads in Pleurodema borellii, revealing an asynchrony between ovarian and testicular differentiation during larval development. We then evaluated the effects of methimazole (a TH synthesis inhibitor) and thyroxine (T4, an endogenous TH agonist) on gonadal development under mesocosm conditions at different larval stages. Methimazole exposure affected testicular morphogenesis more profoundly during later stages, leading to a disorganized morphology, that is, with poorly defined seminiferous tubules, indistinct cysts of spermatogonia, and scattered germ and somatic cells. Early exposure to T4 affected testicular organization as well, while later exposure accelerated differentiation. In ovaries, the timing of T4 exposure significantly influenced lobulation and ovarian cavity formation, with early exposure exerting greater effects than late exposure. These findings suggest that gonadal differentiation appears to reflect an early sensitivity or response to initial TH signals during premetamorphic stages. Collectively, our results highlight the importance of THs in coordinating early gonadal development, reflecting the complexity of endocrine regulation in amphibian sexual differentiation, likely involving interactions with other hormonal axes such as corticosteroids and sex steroids.

The growth of teeth and jaw bones is intimately linked in vertebrates, especially in mammals due to their specialized dentition and limited body growth. However, the relative patterns of growth and level of integration (i.e., co-variation) of these structures are insufficiently known, which hinders our ability to understand how the jaw bones accommodate the diverse dental shapes and eruption patterns observed in mammals. Here, we studied the cranial ontogenetic series of 23 ungulate species among artiodactyls, perissodactyls, and hyracoids having different dental shapes and eruption patterns. We evaluated the variation of the teeth-palate complex, as well as the co-variation of teeth and palate during growth using 3D geometric morphometrics. We found a major ontogenetic component common to all the species studied, corresponding to an elongated dental row relative to the palate in juveniles and vice versa in adults. This pattern agrees with the prolonged growth of the palate as compared to teeth during development but is also reminiscent of an intraspecific allometric pattern previously observed in some dwarf ungulates. Moreover, most artiodactyls, especially ruminants, departed from other ungulates in having a higher co-variation between the dental row and the palate. This stronger integration seen in ruminants might be associated with their inherited rapid growth and relatively fast eruption pattern. This is in contrast to ungulates with late eruption of last molars, whose teeth-palate complex might be less constrained, but further investigation is needed to substantiate these hypotheses and better understand the factors influencing covariations within the upper jaw.

Toxodonts constitute a group of extinct native South American ungulates that have been subject of extensive paleobiological research. Among the traits analyzed, enamel crest complexity (ECC; through fractal dimension) and occlusal surface tooth area (OTA) have recently been studied. However, they have not yet been applied to evaluate differences between ontogenetic stages, (e.g., juveniles, subadults, and adults). Here, we analyzed these traits in the p2-m3 of three species of Toxodontidae, Adinotherium ovinum (n = 8), Nesodon imbricatus (n = 11), and Toxodon platensis (n = 19), along ontogeny by standardized major axis regressions using OTA of m1 as an age proxy, and compared adult and young individuals (i.e., m3 not fully erupted) by Kruskal-Wallis test. Our results showed that ECC decreases with age in all teeth, and p2-m1 seems to share a common slope for Adinotherium and Nesodon. Kruskal-Wallis test showed significant differences between age and species in p3 and molars, with young individuals having higher ECC values than adults. There is a decreasing trend in ECC values from A. ovinum (highest), through N. imbricatus (intermediate), to T. platensis (lowest). These differences are more pronounced from m1 to m3. We conclude that both ECC and OTA can serve as effective tools for differentiating adult toxodonts from those that have not yet reached adulthood. The lower ECC in adult molars may be due to crown simplification during ontogeny, as teeth wear over time by abrasion from food particles during chewing. Conversely, OTA increases in adults as a mixed effect of wear and the larger size of their teeth compared to younger individuals.

Understanding how genomic information is selectively utilized across different life stages is essential for deciphering the developmental and evolutionary strategies of metazoans. In holometabolous insects, the dynamic expression of genes enables distinct functional adaptations at embryonic, larval, pupal, and adult stages, likely contributing to their evolutionary success. While Drosophila melanogaster (D. melanogaster) has been extensively studied, less is known about the evolutionary dynamics that could govern stage-specific gene expression. To address this question, we compared the distribution of stage-specific genes, that is, genes expressed in temporally restricted developmental stages, across the development of D. melanogaster and Aedes aegypti (A. aegypti). Using tau-scoring, a computational method to determine gene expression specificity, we found that, on average, a large proportion of genes (20%–30% of all protein-coding genes) in both species exhibit restricted expression to specific developmental stages. Phylostratigraphy analysis, a method to date the age of genes, further revealed that stage-specific genes fall into two major categories: highly conserved and recently evolved. Notably, many of the recently evolved and stage-specific genes identified in A. aegypti and D. melanogaster are restricted to Diptera order (20%–35% of all stage-specific genes), highlighting ongoing evolutionary processes that continue to shape life-stage transitions. Overall, our findings underscore the complex interplay between gene evolutionary age, expression specificity, and morphological transformations in development. These results suggest that the attraction of genes to critical life-stage transitions is an ongoing process that may not be constant across evolutionary time or uniform between different lineages, offering new insights into the adaptability and diversification of dipteran genomes.