Involvement of Notch and Delta genes in spider segmentation

Abstract

It is currently debated whether segmentation in different animal phyla has a common origin and shares a common genetic mechanism. The apparent use of different genetic networks in arthropods and vertebrates has become a strong argument against a common origin of segmentation. Our knowledge of arthropod segmentation is based mainly on the insect Drosophila, in which a hierarchical cascade of transcription factors controls segmentation. The function of some of these genes seems to be conserved among arthropods, including spiders, but not vertebrates. The Notch pathway has a key role in vertebrate segmentation (somitogenesis) but is not involved in Drosophila body segmentation. Here we show that Notch and Delta genes are involved in segmentation of another arthropod, the spider Cupiennius salei. Expression patterns of Notch and Delta, coupled with RNA interference experiments, identify many similarities between spider segmentation and vertebrate somitogenesis. Our data indicate that formation of the segments in arthropods and vertebrates may have shared a genetic programme in a common ancestor and that parts of this programme have been lost in particular descendant lineages.

Mouse miRNA-709 directly regulates miRNA-15a/16-1 biogenesis at the posttranscriptional level in the nucleus: evidence for a microRNA hierarchy system

“…It is generally believed that biological processes are controlled by activating a hierarchical cascade of interdependent regulators, such as transcription factors or protein kinases [26,27]. By illustrating that a miRNA can regulate the biogenesis of other miRNAs, the results of the present study suggest that certain miRNAs can serve as a novel group of interdependent regulators at post-transcriptional level, in a so-called "miRNA hierarchy system" (Supplementary information, Figure S9).…”

Early origin of the bilaterian developmental toolkit

“…A more complicated issue is that of segmentation. Segmentation is distinct from serial repetition, and the Delta-Notch signalling system is involved in defining segmental boundaries in vertebrates and spiders (where Notch patterns the ectoderm, rather than the mesoderm, as in vertebrates) (Stollenwerk et al 2003;Tautz 2004;Pueyo et al 2008;reviewed in Erwin 2006). While the Notch signalling pathway is present in cnidarians, the Delta-Notch cascade appears to be a later innovation.…”

“…The complexity of this toolkit varies as new studies and broader comparative studies are reported, but minimally includes the following: anterior/posterior (A/P) patterning with seven or eight HOX genes (de Rosa et al 1999;Balavoine et al 2002), and the associated microRNA responsible for inhibiting translation of HOX mRNAs (de Robertis 2008); the HOX genes part of a larger super cluster of at least eight other ANTP-class genes including the ParaHox and NK cluster genes (Butts et al 2008); dorsal/ventral (D/V) patterning controlled by the sog/chordin dpp/ BMP2/4 system (Arendt & Nubler-Jung 1994;De Robertis & Sasai 1996); anterior patterning via ems/ Emx and otd/Otx and a tripartite brain (Arendt & Nubler-Jung 1999;Reichert & Simeone 2001;Arendt et al 2008) with posterior patterning via evenskipped/evx and caudal/cdx; segmentation through engrailed and Delta -Notch (Holland et al 1997;Balavoine & Adoutte 2003;Stollenwerk et al 2003;Tautz 2004); eye formation controlled by a dense network of genes, including Pax6 and ey (Quiring et al 1994;Halder et al 1995;Gehring 2004), but see Arendt et al (2004) and Fernald (2000); endoderm formation and a regionalized through gut via GATA transcription factors, brachyury and goosecoid (Arendt et al 2001); heart formation via Nkx2.5/tinman (Harvey 1996;Bodmer & Venkatesh 1998;Olson 2006); and distal-less involvement in appendage formation (Panganiban et al 1997;Panganiban & Rubenstein 2002;Pueyo & Couso 2005). The pattern of acquisition of microRNAs tracks increasing morphological complexity and provides important information on the evolution of developmental control (Sempere et al 2006;Gimson et al 2008;Wheeler et al 2009).…”

Changing cell behaviours during beetle embryogenesis correlates with slowing of segmentation

“…Typically if variation exists in segment period, it is simply a gradual decrease in segmentation rate as segmentation 'winds down' in the posterior of the embryo 6 or a brief initial period of rapid addition prior to a more regular rate 7 . A clock mechanism for regulating segmentation has recently been extended to sequentially segmenting arthropods [8][9][10][11][12][13] . Support for a clock includes a clear demonstration of molecular oscillations in the flour beetle, Trobolium casteneum 14 .…”