Achaearanea tepidariorum, the common American house spider is an emerging species for developmental biology with the increasing availability of micro-injections to facilitate these studies. Due to their short generation time and ability to use techniques such as RNAi and in-situ hybridization at the earliest of stages in embryonic development, they have become a model organism to study.
A dynamic expression of genes is required throughout the embryo for proper anterior to posterior development. Orthodenticle pRNAi embryos blocks the expression of these genes, thus inhibiting segmentation. Gene expression across a field of cells is required for anterior regionalization and segmentation. These positional values are specified via a morphogen-independent mechanism (Pechmann, 2009).
The development of this spider undergoes a 16 cell stage before forming a blastoderm via a series of gene expressions from anterior to posterior regions of the embryo. Wnt genes are part of a family responsible for cell signaling pathways and many of these have played key roles in developmental biology. Wnt8 gene specifically is responsible for posterior development in Achaearanea tepidariorum through regulation of growth-zone cells in spiders. Knockout of the Wnt8 gene via parental RNAi results in misregulation of Delta (Dl), Hairy (h), Twist (twi), and Caudal (cad) causing a failure of opisthosoma development due to the lack of establishment of a posterior growth zone (McGregor, 2008).
Pechmann, M., A. P. McGregor, et al. (2009). “Dynamic gene expression is required for anterior regionalization in a spider.” Proc Natl Acad Sci U S A 106(5): 1468-1472.
McGregor, A. P., M. Pechmann, et al. (2008). “Wnt8 is required for growth-zone establishment and development of opisthosomal segments in a spider.” Curr Biol 18(20): 1619-1623.
Oda, H., O. Nishimura, et al. (2007). “Progressive activation of Delta-Notch signaling from around the blastopore is required to set up a functional caudal lobe in the spider Achaearanea tepidariorum.” Development 134(12): 2195-2205.