Mesodermal organogenesis in the embryo of the primitive moth,Neomicropteryx nipponensis Issiki (Lepidoptera, Micropterygidae)

Evolution of a cytoplasmic determinant: evidence for the biochemical basis of functional evolution of the novel germ line regulator oskar

Germ line specification is essential in sexually reproducing organisms. Despite their critical role, the evolutionary history of the genes that specify animal germ cells is heterogeneous and dynamic. In many insects, the gene oskar is required for the specification of the germ line. However, the germ line role of oskar is thought to be a derived role resulting from co-option from an ancestral somatic role. To address how evolutionary changes in protein sequence could have led to changes in the function of Oskar protein that enabled it to regulate germ line specification, we searched for oskar orthologs in 1,565 publicly available insect genomic and transcriptomic data sets. The earliest-diverging lineage in which we identified an oskar ortholog was the order Zygentoma (silverfish and firebrats), suggesting that oskar originated before the origin of winged insects. We noted some order-specific trends in oskar sequence evolution, including whole gene duplications, clade-specific losses, and rapid divergence. An alignment of all known 379 Oskar sequences revealed new highly conserved residues as candidates that promote dimerization of the LOTUS domain. Moreover, we identified regions of the OSK domain with conserved predicted RNA binding potential. Furthermore, we show that despite a low overall amino acid conservation, the LOTUS domain shows higher conservation of predicted secondary structure than the OSK domain. Finally, we suggest new key amino acids in the LOTUS domain that may be involved in the previously reported Oskar−Vasa physical interaction that is required for its germ line role.

Embryogenesis of Heliconius erato (Lepidoptera, Nymphalidae): a contribution to the anatomical development of an evo-devo model organism

This study reports on the embryogenesis of Heliconius erato phyllis between blastoderm formation and the prehatching larval stage. Syncytial blastoderm formation occurred approximately 2 h after egg laying (AEL) and at about 4 h, the cellular blastoderm was formed. The germ band arose from the entire length of the blastoderm, and rapidly became compacted occupying approximately two-thirds of the egg length. At about 7 h AEL, protocephalon and protocorm differentiation occurred. Continued proliferation of the germ band was followed by penetration into the yolk mass, forming a C-shaped embryo at about 10 h. Approximately 12 h AEL, the gnathal, thoracic and abdominal segments became visible. The primordium of the mouthparts and thoracic legs formed as paired evaginations, while the prolegs formed as paired lobes. At about 30 h, the embryo reversed dorsoventrally. Approximately 32 h AEL, the protocephalon and gnathal segments fused, shifting the relative position of the rudimentary appendages in this region. At about 52 h, the embryo was U-shaped in lateral view and at approximately 56 h, the bristles began evagination from the larval cuticle. Larvae hatched at about 72 h. We found that H. erato phyllis followed an embryonic pattern consistent with long-germ embryogenesis. Thus, we believe that H. erato phyllis should be classified as a long-germ lepidopteran. The study of H. erato phyllis embryogenesis provided a structural glimpse into the morphogenetic events that occur in the Heliconius egg period. This study could help future molecular approaches to understanding the evolution of Heliconius development.