Coordinated and conserved expression of alphoid repeat and alphoid repeat-tagged coding sequences.

We have found an alpha-like simple-sequence DNA repeat that is differentially expressed during early embryogenesis in both chick and zebrafish. Before and during the primitive streak stage, transcripts of the alphoid repeat sequence were ubiquitously expressed throughout zebrafish and chick embryos. After headfold formation, expression was limited to the cardiac neural crest, the head, and the heart. Two types of alphoid repeat sequence transcripts were identified: alphoid repeat RNA and alphoid repeat-tagged mRNA (ESalphaT). Several of the ESalphaTs were identified by (1) searching expressed sequence tag databases, (2) arbitrary rapid amplification of cDNA ends (RACE), and (3) screening embryonic cDNA libraries. The alphoid element was located in the 3' untranslated region of one ESalphaT that was obtained by RACE. The ESalphaT sequences encoded a variety of different types of proteins, but all were expressed within tissues that were positive for the alphoid repeat RNA. The presence of two types of coordinately expressed alphoid-like repeat transcripts in maternal RNA with subsequent restriction to the head and heart, and the conservation of these features in disparate vertebrate embryos, suggest that the alphoid repeat sequence may serve as a control element in the gene regulation network. Copyright 2003 Wiley-Liss, Inc.