SPFKH1 ENCODES A TRANSCRIPTION FACTOR IMPLICATED IN GUT FORMATION DURING SEA-URCHIN DEVELOPMENT

A member of the forkhead class of transcription factors from sea urchi ns (Spfkh1) that is expressed specifically in the endoderm of developi ng embryos has been identified. Spfkh1 was expressed transiently in th e embryo, with peak levels of messenger ribonucleic acid (mRNA) accumu lating at the time endoderm invaginated into the interior of the embry o. Expression was limited to the invaginating endoderm in the early ga strula, then became further restricted to the base of the invaginating gut at the mid-gastrula stage. Expression diminished by the end of ga strulation. This expression pattern indicates that Spfkh1 mRNA accumul ates in endodermal cells as they invaginate, but disappears rapidly in endodermal cells that undergo convergent extension. Treatment of embr yos during cleavage stages with lithium or phorbol esters caused an in crease in Spfkh1 mRNA accumulation and expanded the domain of expressi on of Spfkh1, suggesting that signaling through the inositol-tris-phos phate protein kinase C (IP3-PKC) signaling pathway is upstream of Spik h1 expression. The expression pattern of Spfkh1 suggests that it is ce ntrally involved in specification and/or differentiation of the gut. D isruption of the extracellular matrix (ECM) prevents formation of the gut, but does not inhibit initiation of Spfkh1 expression. Embryos arr ested prior to gastrulation continued to express Spfkh1 well past time it was downregulated in normal embryos, suggesting the ECM or cell mo vement is required for the decrease in Spfkh1 mRNA during gastrulation .