Evolution of the thyroid: Anterior–posterior regionalization of theOikopleuraendostyle revealed byOtx,Pax2/5/8, andHox1expression

Abstract

The thyroid in vertebrates and its homolog, the endostyle in nonvertebrate chordates, share a molecular code for dorsoventral patterning. Little is yet known, however, about mechanisms that pattern the endostyle's anterior-posterior (AP) axis. To extend our understanding of thyroid development and evolution, we studied Oikopleura dioica, a larvacean urochordate that retains a chordate body plan as adults. Transcription factor expression domains revealed AP regionalization of the endostyle, with expression of Otx rostrally, Hox1 caudally, and two Pax2/5/8 paralogs centrally. Comparative analysis suggested that the endostyle of stem chordates expressed orthologs of these genes and that ancestral subfunctions partitioned differentially among lineages. Because the ordered expression of Otx, Pax2/5/8, and Hox1 displays patterning in both the endodermally derived endostyle and the ectodermally derived central nervous system, we propose that this gene set belonged to the developmental genetic toolkit of stem bilaterians and repeatedly provided AP positional information in various developmental situations.

Identification of the Endostyle as a Stem Cell Niche in a Colonial Chordate

“…It exhibits unique spatial and temporal features with site-specific factors that were previously implicated in developmental regulation and stem cell maintenance in other systems. These include thyroid hormones, serotonin, Otx, Hox1, Pax 2/5/8, PL10 and Cadherin (Canestro et al, 2008; Dunn, 1980; Hiruta et al, 2005; Nilsson et al, 1988; Pennati et al, 2001; Rosner et al, 2006; Rosner et al, 2007). The canonical Wnt pathway was shown to be involved in stem cell regulation and proliferation in various stem cells niches (reviewed in Morrison and Spradling, 2008; Scadden, 2006).…”

Metallothioneins of the urochordateOikopleura dioicahave Cys-rich tandem repeats, large size and cadmium-binding preference

“…14 Appendicularians are also ecologically relevant because they contribute to the vertical transport of carbon to deep ocean through the rapid sinking of fecal pellets and discarded houses. [15][16][17] Among Appendicularians, Oikopleura dioica is the most studied species, and it is becoming a new laboratory model for comparative genetic and genomic analyses, [18][19][20][21][22] developmental biology studies, [23][24][25][26][27][28][29][30] as well as ecological and toxicological investigations. [31][32][33][34] The ecological relevance of Appendicularians together with the potential of O. dioica as an experimental model [35][36][37][38] prompted us to survey the MTs of O. dioica to characterize the MT system of an Appendicularian species.…”

Oikopleura dioicaculturing made easy: A Low‐Cost facility for an emerging animal model inEvoDevo

“…O. dioica provides an excellent animal model for studies in developmental biology, as fertilized eggs develop into transparent embryos easy to follow under a stereomicroscope without any further manipulation. Many developmental studies have already described its early embryogenesis (Delsman, 1910;Nishida, 2008), its stereotyped cell fate map (Fujii et al, 2008;Stach et al, 2008), as well as the development of several body structures such as the notochord (Bassham and Postlethwait, 2000;Nishino et al, 2001), the central nervous system (Cañestro et al, 2005;Soviknes et al, 2007), placodal sensory organs , the digestive system (Burighel and Brena, 2001;Cañestro et al, 2010), gonad development (Ganot et al, 2007;Ganot et al, 2008), or the homolog of the thyroid Cañestro et al, 2008). iv).…”