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PubMed2023

The gastropod Lottia peitaihoensis as a model to study the body patterning of trochophore larvae.

The body patterning of trochophore larvae is important for understanding spiralian evolution and the origin of the bilateral body plan. However, considerable variations are observed among spiralian lineages, which have adopted varied strategies to develop trochophore larvae or even omit a trochophore stage. Some spiralians, such as patellogastropod mollusks, are suggested to exhibit ancestral traits by producing equal-cleaving fertilized eggs and possessing "typical" trochophore larvae. In recent years, we developed a potential model system using the patellogastropod Lottia peitaihoensis (= Lottia goshimai). Here, we introduce how the species were selected and establish sources and techniques, including gene knockdown, ectopic gene expression, and genome editing. Investigations on this species reveal essential aspects of trochophore body patterning, including organizer signaling, molecular and cellular processes connecting the various developmental functions of the organizer, the specification and behaviors of the endomesoderm and ectomesoderm, and the characteristic dorsoventral decoupling of Hox expression. These findings enrich the knowledge of trochophore body patterning and have important implications regarding the evolution of spiralians as well as bilateral body plans.

Animals↗

PubMed1975

[Effect of actinomycin D and sibiromycin on the embryonic and larval development of Nereis virens (Sars.)].

The morphogenetic function of nuclear apparatus has been studied by means of "chemical enucleation" using actinomycin D (60 microgram/ml, 3 hrs) and sibiromycin (10--100 microgram/ml, 3 hrs) at different developmental stages of Nereis virens (Sars.). The embryos were subjected to the effect of the inhibitors at the successive stages every 6 hrs beginning from the fertilization. The development proceeded in the normal way til the throchophore stage in spite of the inhibition of DNA-dependent RNA synthesis what agrees with the concept of P. P. Ivanov on the existence in Polychaeta of a developmental tendency to trochophore. The first period of morphogenetic activity of the genome which ensures the transition from trochophore to metatrochophore coincides with the gastrula stage and the second period which ensures the transformation of metatrochophore into nectochaete with the final phases of the trochophore stage.

Animals↗

PubMed1992

[Study on the effect of bromoacetamide upon the development of snail eggs].

This paper deals with the influence of bromoacetamide on the development of snail eggs, its effect on inducing diapause of snail eggs at different developmental stages (blastula, gastrula, trochophore and veliger) both at different concentrations of bromoacetamide at the same time and at same concentration at different times. Besides, the oviposition of the snails and the eggs within snails have also been studied. The results are as follows: 1. When the snail eggs were immersed in bromoacetamide at concentrations of 0.034ppm-0.067ppm, deformation of snail eggs appeared from unicellular to gastrula stages, but it was not observed after the trochophore-veliger stages. When the eggs at different stages were separately immersed in bromoacetamide, they were all found deformed. The molluscicidal concentration for inducing deformation of eggs was higher at the trochophore-veliger and metamophotic stages than that at the blastula and gastrula stages (Figs. 1-5). 2. After immersed in bromoacetamide solution, the development of the snail eggs were obviously retarded. The effects varied with different concentrations. Within the same exposure time, the higher the bromoacetamide concentration, the higher the diapause rate. 3. The longer the immersion time, the lower concentration was needed to delay the development and the lower hatching rate was for the eggs at the same or different stages. 4. After treatment with bromoacetamide, the average number of eggs laid by a female snail was reduced. 5. By using 3H-labeled bromoacetamide, it was found that the radioactivity of 3H-labeled bromoacetamide per hundred snail eggs was raised along with the increasing of the molluscicide concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetamides↗

PubMed1977

[Effect of actinomycin D and sibiromycin on 3H-thymidine incorporation into the early developmental stages of Nereis virens Sars].

The Nereis virens embryos at the stages of 2, 8, 16 and 32 blastomeres end of cleavage and beginning of rotation were placed in the actinomycin D or sibiromycin solutions and the effect of antibiotics on 3H-thymidine incorporation during cleavage, at the beginning of rotation and in trochophore was determined by means of autoradiography after careful washing the embryos off. Under the effect of actinomycin D the intensity of 3H-thymidine incorporation during cleavage decreased insignificantly, at the gastrula stage somewhat exceeded that in the control, and at the stages of trochophore formation decreased twice. At the later stages it approached the normal level. In the experiments with sibiromycin which proved to have more distinct inhibitory effect, the stage of trochophore formation was also found to be the most sensitive to the antibiotic.

Animals↗

PubMed2023

Emerging trends in the study of spiralian larvae.

Many animals undergo indirect development, where their embryogenesis produces an intermediate life stage, or larva, that is often free-living and later metamorphoses into an adult. As their adult counterparts, larvae can have unique and diverse morphologies and occupy various ecological niches. Given their broad phylogenetic distribution, larvae have been central to hypotheses about animal evolution. However, the evolution of these intermediate forms and the developmental mechanisms diversifying animal life cycles are still debated. This review focuses on Spiralia, a large and diverse clade of bilaterally symmetrical animals with a fascinating array of larval forms, most notably the archetypical trochophore larva. We explore how classic research and modern advances have improved our understanding of spiralian larvae, their development, and evolution. Specifically, we examine three morphological features of spiralian larvae: the anterior neural system, the ciliary bands, and the posterior hyposphere. The combination of molecular and developmental evidence with modern high-throughput techniques, such as comparative genomics, single-cell transcriptomics, and epigenomics, is a promising strategy that will lead to new testable hypotheses about the mechanisms behind the evolution of larvae and life cycles in Spiralia and animals in general. We predict that the increasing number of available genomes for Spiralia and the optimization of genome-wide and single-cell approaches will unlock the study of many emerging spiralian taxa, transforming our views of the evolution of this animal group and their larvae.

Animals↗

PubMed1978

Morphogenesis of larval cuticle in the polychaete Phragmatopoma lapidosa. A correlated scanning and transmission electron microscopic study from egg envelope formation to larval metamorphosis.

The development of the egg envelope and its incorporation into the larval cuticle of the polychaete Phragmatopoma lapidosa, was studied by correlative scanning and transmission electron microscopy. The mature egg possesses an envelope composed of five zones including an outer granular zone formed by the tips of the egg microvilli. The formation of the granules is described and their functions are discussed. The entire egg envelope is retained as the larval cuticle up to the 16 h trochophore stage. From this stage to about the 60 h larval stage, the envelope is gradually lost and replaced by a cuticle consisting of branching microvilli. The cuticle of the 20 day larva is composed of highly branching microvilli penetrating a homogeneous electron opaque cuticle. The possible functions of the cuticle among the Annelida are discussed.

Animals↗

PubMed1978

Ultrastructure of a cephalic sensory organ in larvae of the gastropod Phestilla sibogae (Aeolidacea, Nudibrachia).

The cephalic sensory organ is a superficial sensory receptor located between the velar lobes at the level of the shell aperture. Three cell types make up this sensory area: (1) six flask-shaped cells bearing numerous cilia: (2) adjacent supporting or accessory cells which have numerous, often branched, microvilli; and (3) vacuolated cells which occupy the center of the area. The flask-shaped cells appear to be the sensory units. These cells have a deep invaginated lumen, with ciliar arising from the cell surface in the lumen oriented either toward the base of the lumen or toward the epidermal surface these cilia, some of which extend slightly above the body surface, are presumed to be non-motile, as they lack (dynein?) arms on the axonemal A tubules and lack striated rootlets. The six flask cells are in intimate contact with the underlying cerebral ganglia and axons from each cell pass into ganglionic tissue. The supporting cells may be sensory, but no direct connection with the nervous system was seen. The function of the central vacuolated cells is not known. This cephalic organ may be a derivative of the original apical tuft of the trochophore stage.

Animals↗