Wasps, beetles and the beginning of the ends

Abstract

Recent papers investigating the genes regulating early embryogenesis in the wasp Nasonia vitripennis and the beetle Tribolium castaneum have provided us with important clues as to how early development is controlled in insects other than higher dipterans such as Drosophila melanogaster. The results of these studies demonstrate that in insects that do not have bicoid, anterior patterning is regulated by a combination of maternal orthodenticle and hunchback. Furthermore, during the evolution of long-germ-band development, Nasonia and Drosophila may have evolved different mechanisms to pattern posterior segments, marginalising the important role of the terminal system in short-germ-band embryos.

Dynamic gene expression is required for anterior regionalization in a spider

“…In Drosophila development the syncytial blastoderm allows transcription factor morphogen gradients, like the Bcd gradient, to directly determine positional values for the expression of target genes and where segmental boundaries eventually will arise (1, 6). In other holometabolous insects an Otd gradient may play a role like Bcd in anterior segmentation (7)(8)(9). However, the cellular blastoderm of many other arthropods does not allow the formation of diffusion gradients (10, 11) and thus requires a different mechanism for providing positional clues across a field of cells.…”

“…RNAi knockdown of otd in Nasonia vitripennis (a wasp) and Tribolium castaneum (a beetle) resulted in loss of anterior segments, presumably as a consequence of a shift of target gene expression toward the anterior pole (8). The fast evolving gene bcd therefore may have usurped a possible ancestral patterning system involving otd in the lineage leading to higher dipterans (7)(8)(9).…”

“…The gradients of Bcd or Otd acting in holometabolous insects depend on the lack of cell membranes in the syncytial blastoderm embryo that allows diffusion of these transcription factors to form gradients (2)(3)(4)(7)(8)(9). The blastoderm stages of many other arthropod embryos, however, are cellularized rather than syncytial, which does not allow the formation of transcription factor diffusion gradients (12)(13)(14)(15)(16).…”

The Wnt and Delta-Notch signalling pathways interact to direct pair-rule gene expression via caudal during segment addition in the spider Parasteatoda tepidariorum

“…Unlike in Parasteatoda, however, cad represses Dl in the Periplaneta SAZ (Chesebro et al, 2013). Furthermore, it is likely that Wnt1 is required for cad expression during posterior development in Tribolium as in Gryllus (Shinmyo et al, 2005;McGregor, 2006;Oberhofer et al, 2014) and a recent study has shown that the graded expression of Tc-cad is required for the dynamic expression of Tc-eve (El-Sherif et al, 2014). This suggests that although there are differences in the regulation of segment addition among short-germ arthropods, the regulation of eve by cad, probably directed by upstream signalling pathways, may have been used ancestrally in arthropods.…”

Cupiennius salei and Achaearanea tepidariorum: Spider models for investigating evolution and development

“…(4,5) After all, many features of Drosophila development are not representative of insects, but comparisons between Nasonia, Tribolium and Drosophila have been rewarding, for example, in understanding how the regulation of anteroposterior (AP) polarity has evolved in this class. (6,7) In addition, more considered sampling among animals can also allow studies of important evolutionary innovations that are not necessarily found in standard model organisms, such as wing spots in butterflies (8) and the production of silk in spiders. (9,10) Outside insects, new models are emerging in the other arthropod classes, such as the crustaceans Parhyale, (11) Artemia (12) and Daphnia, (13) and the myriapods Lithobius, (14) Strigamia (15) and Glomeris.…”