  During embryonic development, a complex organism is formed from a single
starting cell. These processes of growth and differentiation are driven by
large transcriptional changes, which are following the expression and activity
of transcription factors (TFs). This study sought to compare TF expression
during embryonic development in a diverse group of metazoan animals:
representatives of vertebrates (Danio rerio, Xenopus tropicalis), a chordate
(Ciona intestinalis) and invertebrate phyla such as insects (Drosophila
melanogaster, Anopheles gambiae) and nematodes (Caenorhabditis elegans) were
sampled, The different species showed overall very similar TF expression
patterns, with TF expression increasing during the initial stages of
development. C2H2 zinc finger TFs were over-represented and Homeobox TFs were
under-represented in the early stages in all species. We further clustered TFs
for each species based on their quantitative temporal expression profiles. This
showed very similar TF expression trends in development in vertebrate and
insect species. However, analysis of the expression of orthologous pairs
between more closely related species showed that expression of most individual
TFs is not conserved, following the general model of duplication and
diversification. The degree of similarity between TF expression between Xenopus
tropicalis and Danio rerio followed the hourglass model, with the greatest
similarity occuring during the early tailbud stage in Xenopus tropicalis and
the late segmentation stage in Danio rerio. However, for Drosophila
melanogaster and Anopheles gambiae there were two periods of high TF
transcriptome similarity, one during the Arthropod phylotypic stage at 8-10
hours into Drosophila development and the other later at 16-18 hours into
Drosophila development.
