Mode Of Embryogenesis Research Articles

Evolutionarily conserved function of the even-skipped ortholog in insects revealed by gene knock-out analyses in Gryllus bimaculatus

Comparing the developmental mechanisms of segmentation among insects with different modes of embryogenesis provides insights on how the function of segmentation genes evolved. Functional analysis of eve by genetic mutants shows that the Drosophila pair-rule gene, even-skipped (eve), contributes to initial segmental patterning. However, eve orthologs tends to have diverse functions in other insects. To compare the evolutionary functional divergence of this gene, we evaluated eve function in a phylogenetically basal insect, the cricket Gryllus bimaculatus. To investigate the phenotypic effects of eve gene knock-out, we generated CRISPR/Cas9 system-mediated mutant strains of the cricket. CRISPR/Cas9 mutagenesis of multiple independent sites in the eve coding region revealed that eve null mutant embryos were defective in forming the gnathal, thoracic, and abdominal segments, consequently shortening the anterior-posterior axis. In contrast, the structures of the anterior and posterior ends (e.g., antenna, labrum, and cercus) formed normally. Hox gene expression in the gnathal, thoracic, and abdominal segments was detected in the mutant embryos. Overall, this study showed that Gryllus eve plays an important role in embryonic elongation and the formation of segmental boundaries in the gnathal to abdominal region of crickets. In the light of studies on other species, the eve function shown in Gryllus might be ancestral in insects.

Short germ insects utilize both the ancestral and derived mode of Polycomb group-mediated epigenetic silencing of Hox genes.

In insect species that undergo long germ segmentation, such as Drosophila, all segments are specified simultaneously at the early blastoderm stage. As embryogenesis progresses, the expression boundaries of Hox genes are established by repression of gap genes, which is subsequently replaced by Polycomb group (PcG) silencing. At present, however, it is not known whether patterning occurs this way in a more ancestral (short germ) mode of embryogenesis, where segments are added gradually during posterior elongation. In this study, two members of the PcG family, Enhancer of zeste (E(z)) and Suppressor of zeste 12 (Su(z)12), were analyzed in the short germ cricket, Gryllus bimaculatus. Results suggest that although stepwise negative regulation by gap and PcG genes is present in anterior members of the Hox cluster, it does not account for regulation of two posterior Hox genes, abdominal-A (abd-A) and Abdominal-B (Abd-B). Instead, abd-A and Abd-B are predominantly regulated by PcG genes, which is the mode present in vertebrates. These findings suggest that an intriguing transition of the PcG-mediated silencing of Hox genes may have occurred during animal evolution. The ancestral bilaterian state may have resembled the current vertebrate mode of regulation, where PcG-mediated silencing of Hox genes occurs before their expression is initiated and is responsible for the establishment of individual expression domains. Then, during insect evolution, the repression by transcription factors may have been acquired in anterior Hox genes of short germ insects, while PcG silencing was maintained in posterior Hox genes.

A new molecular logic for BMP-mediated dorsoventral patterning in the leech Helobdella.

Bone morphogenetic protein (BMP) signaling is broadly implicated in dorsoventral (DV) patterning of bilaterally symmetric animals [1-3], and its role in axial patterning apparently predates the birth of Bilateria [4-7]. In fly and vertebrate embryos, BMPs and their antagonists (primarily Sog/chordin) diffuse and interact to generate signaling gradients that pattern fields of cells [8-10]. Work in other species reveals diversity in essential facets of this ancient patterning process, however. Here, we report that BMP signaling patterns the DV axis of segmental ectoderm in the leech Helobdella, a clitellate annelid (superphylum Lophotrochozoa) featuring stereotyped developmental cell lineages, but the detailed mechanisms of DV patterning in Helobdella differ markedly from fly and vertebrates. In Helobdella, BMP2/4s are expressed broadly, rather than in dorsal territory, whereas a dorsally expressed BMP5-8 specifies dorsal fate by short-range signaling. A BMP antagonist, gremlin, is upregulated by BMP5-8 in dorsolateral, rather than ventral territory, and yet the BMP-antagonizing activity of gremlin is required for normal ventral cell fates. Gremlin promotes ventral fates without disrupting dorsal fates by selectively inhibiting BMP2/4s, not BMP5-8. Thus, DV patterning in the development of the leech revealed unexpected evolutionary plasticity of the conserved BMP patterning system, presumably reflecting its adaptation to different modes of embryogenesis.

Evolution of an anterior morphogenetic center in long germ insects

Plenary session I: Developmental Biology Symposium: Evolution of developmental regulatory systems Program/Abstract # 25 Evolution of an anterior morphogenetic center in long germ insects Claude Desplan, Ava Brent, Eugenia Olesnicky, Miriam Rosenberg, Claude Desplan Department of Biology, NYU, New York, NY, USA In the derived long-germ mode of insect development, the embryo occupies the entire egg and all segments form simultaneously in a syncytial environment. In Drosophila, this patterning is mediated by a gradient of Bicoid protein but this is a new invention of higher Diptera. We analyzed axis formation in Nasonia, a wasp (Hymenoptera) that has developed long germ independently from higher Diptera. Like bicoid in Drosophila, Nasonia orthodenticle (Nv-otd1) maternal mRNA is localized at the anterior of the eggwhere it generates amorphogenetic gradient. It is also localized at the posterior where it induces the expression of posterior genes much earlier than in short germ insects, where their expression is delayed to the growth zone. mRNA localization in Nasonia also mediates permissive functions achieved by Bicoid in flies: caudal mRNA is posteriorly localized to restrict its function to posterior segments. In Drosophila, this is achieved by translational regulation of caudal mRNA by Bicoid. giant mRNA is localized, anteriorly, where it represses mid-body genes such as Kruppel. This repression thus occurs early in spite of the much slower early Nasonia developmental timing that would not allow zygotic Giant to be expressed early enough to repressKruppel. Therefore, the network ofNasonia developmental genes is made of very similar genes to flies, and these exhibit similar crossinteractions. However, the network has been modified in Nasonia and relies on localized maternal genes to accommodate developmental changes such as the absence of bicoid, the slowermode of development, or the long germ mode of embryogenesis. doi:10.1016/j.ydbio.2009.05.033 Program/Abstract # 26 How many ways to make a chordate: Comparison of the developmental programs of ascidians and vertebrates Daniel Sobral, Andrea Pasini, Patrick Lemaire IBDML, CNRS-Universite de la Mediterranee, Marseille, France Tunicates, including ascidians are the closest living relatives of vertebrates, with whom they share a tadpole-like larval form. At the morphological and embryological level, however, vertebrates share structures and processes that have been lost in ascidians. For example, tail extension in ascidians relies on cell rearrangements and intercalation, rather than on the growth of a tailbud as in vertebrates. More generally, the ascidian stereotyped embryogenesis departs from that of vertebrates, as it is based on invariant cell lineages. We are trying to understand how chordates can form similar tadpole-like larvae in spite of apparently different developmental strategies. We have addressed this question by quantifying the extent of divergence of gene expression profiles between orthologs from Ciona intestinalis and the teleost fishDanio rerio.We found a surprisingly high level of divergence at all stages, including the phylotypic stage. This extent of divergence was similar for developmental regulators and their effectors, but differed between tissues. The muscle program was best conserved in spite of the lack of somites in Ciona. Surprisingly, we found that a complex genetic program similar to that found in vertebrates to regulate the formation of successive somites acts along the ascidian tail, where it has been recruited for A/P epidermal patterning. doi:10.1016/j.ydbio.2009.05.034 Program/Abstract # 27 Diversity of X-chromosome inactivation patterns during early mammalian development Ikuhiro Okamoto, Veronique Duranthon, Dominique Thepot, Nathalie Peynot, Jean Paul Renard, Edith Heard Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR3215, INSERM U934, 26 rue d'Ulm, Paris 75005, France Biologie du Developpement et de la Reproduction, INRA 78 352 Jouy en

Polyembryony in parasitic wasps: evolution of a novel mode of development.

Major developmental innovations have been associated with adaptive radiations that have allowed particular groups of organisms to occupy empty ecospace. Well-known developmental novelties associated with the conquest of new habitats include the evolution of the tetrapode limb, allowing the radiation of vertebrates into a terrestrial habitat, and formation of insect wings that permitted their dispersal into the air. However, an understanding of the evolutionary forces and molecular mechanisms behind developmental novelties still remains tenuous. A little-studied adaptive radiation in insects from the developmental perspective is the evolution of parasitism. The parasitic lifestyle has allowed parasitic insects to occupy a novel ecological niche where they have evolved a plethora of life history strategies and modes of embryogenesis, developing on or within the body of the host. One of the most striking adaptations to development within the body of the host includes polyembryonic development, where certain wasps form clonally up to 2000 embryos from a single egg. Taking advantage of well-established insect phylogeny, techniques developed in a model insect, the fruit fly, and a wealth of knowledge in comparative insect embryology, we are starting to tease apart the evolutionary events that have led to this novel mode of development in insects.

Leg Formation in the Honeybee Broodmite Varroa jacobsoni (Acarina: Varroidae)

Embryonic development in the parasitic honeybee mite Varroa jacobsoni Oudemans 1904 was studied by scanning electron microscopy with special emphasis on the formation of the legs (pedes). Immediately after segmentation of the germ band stage the anlagen of all the 6 pairs of extremities are formed in the prosoma. Subsequently, the 4 pairs of pedes are differentiated simultaneously. Therefore, already in the embryonic phase an 8-legged intraovarian instar is occuring and, in contrast to most of the closely related Gamasida mites, no 6-legged egg larva is formed. This direct development of all pairs of pedes results in a protonymph hatching several hours after oviposition of the egg. Presumably, such an abbreviated mode of embryogenesis has to be interpreted as an adaptation to the short time available for reproduction during the capped period in the development of the host

Origin and Ontogenesis of Somatic Embryos in Hevea brasiliensis (Euphorbiaceae)

In Hevea, currently described culture conditions allow the induction of two modes of embryogenesis in callus formed on excised portions of the internal integument of immature seeds. One mode is of unicellular origin and is transitory, only resulting in the production of globular proembryos. The other is of multicellular origin and produces embryos. Specific culture conditions appear to favor one or the other mode of development in a given genotype. The ontogenesis of embryos of multicellular origin bypasses the classical stages of zygotic embryogenesis. The structural abnormalities observed in most somatic embryos are probably responsible for the low germination rates obtained.

ORIGIN AND ONTOGENESIS OF SOMATIC EMBRYOS IN HEYEA BRASILIENSIS (EUPHORBIACEAE)

In Hevea, currently described culture conditions allow the induction of two modes of embryogenesis in callus formed on excised portions of the internal integument of immature seeds. One mode is of unicellular origin and is transitory, only resulting in the production of globular proembryos. The other is of multicellular origin and produces embryos. Specific culture conditions appear to favor one or the other mode of development in a given genotype. The ontogenesis of embryos of multicellular origin bypasses the classical stages of zygotic embryogenesis. The structural abnormalities observed in most somatic embryos are probably responsible for the low germination rates obtained.

クロマツの胚発生の組織化学的研究

On the mode of embryogenesis in Pinus thunbergii, its course can be divided approximately into six stages.With histochemical methods the appearance and disappearance of proteins and polysaccharides are studied. The localization of these substances in the different stages of embryogenesis is elucidated.In the cells of the middle part of prothallium where the suspensor elongates, abundant starch and proteins begin to appear in the proembryo stage. These substances rapidly increase and reach the maximum state in the case of proteins when the suspensor has elongated to half of its full length, or in the case of starch when the embryo begins to differentiate into two portions. These substances disappear when the cells containing them break down. The proteins completely disappearjust after the embryo initial has formed, and after some intervals the most of starch gradually decreases its amount till the basal portion of embryo begins to differentiate into two parts though a small quantity of them remains in the tissue surrounding the embryo. From the above facts it may be concluded that these substances are converted into soluble state and serve as nutrients for the early development of embryo.Protein granules begin to accumulate in the remaining prothallium from the stage of suspensor elongation and in the embryo from the stage of cotyledon differentiation. These protein granules gradually increase their amounts and in the mature stage of embryo attain to large quantities. Also many starch grains and much of amorphous polysaccharides begin to accumulate in the basal portion of embryo from the stage of cotyledon differentiation. These substances are considered as the storage material for the coming germination.