Planarian homeobox gene Dtprd-1 is expressed in specific gland cells and belongs to a new family within the paired-like class
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The genome of the planarian (Platyhelminthes; Turbellaria; Tricladida) Dugesia (Girardia) tigrina includes a paired-like type of homeobox gene. The Dtprd-1 gene encodes a protein of 382 amino acids. The open reading frame of Dtprd-1 is interrupted by two short introns of 65 and 56 bp, and one long intron of 4.8 kb. The intron positions are not located in the homeobox and are not shared with any other known paired-like gene. The Dtprd-1 homeodomain conserves most of the residues characteristic of the paired-like class. Similarity with other members of this class is low, except with the rat, mouse and Caenorhabditis elegans proteins PHD1, Uncx-4.1 and unc-4, with 86–83% of similarity in the homeodomain, plus several peptides in the flanking regions. Such proteins share specific residues in their homeodomains that can be used to define a new family in the paired-like class of genes. The spatial distribution of gene transcript and product in adult tissues, as revealed by RT-PCR, northern blots and polyclonal antibody, demonstrates that Dtprd-1 is highly expressed in cyanophilic gland cells located in the ventral parenchyma close to the nervous system. No expression is observed during the early stages of regeneration (0–3 days). This suggests a possible role for this homeobox gene within these secretory gland cells, but not in the pattern formation mechanisms known to occur at the early stages of regeneration.
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