We previously determined that yquem harbors a mutation in the gene encoding uroporphyrinogen decarboxylase (UROD), the fifth enzyme in heme biosynthesis, and established zebrafish yquem (yqe tp61 ) as a vertebrate model for human hepatoerythropoietic porphyria (HEP). Here we report that six exocrine peptidase precursor genes, carboxypeptidase A, trypsin precursor, trypsin like, chymotrypsinogen B1, chymotrypsinogen 1-like, and elastase 2 like, are downregulated in yquem/urod (2/ 2), identified initially by microarray analysis of yquem/urod zebrafish and, subsequently, confirmed by in situ hybridization. We then determined downregulation of these six zymogens specifically in the exocrine pancreas of sauternes (sau tb223 ) larvae, carrying a mutation in the gene encoding d-aminolevulinate synthase (ALAS2), the first enzyme in heme biosynthesis. We also found that ptf1a, a transcription factor regulating exocrine zymogens, is downregulated in both yquem/urod (2/2) and sau/alas2 (2/2) larvae. Further, hemin treatment rescues expression of ptf1a and these six zymogens in both yquem/urod (2/2) and sauternes/alas2 (2/2) larvae. Thus, it appears that heme deficiency downregulates ptf1a, which, in turn, leads to downregulation of exocrine zymogens. Our findings provide a better understanding of heme deficiency pathogenesis and enhance our ability to diagnose and treat patients with porphyria or pancreatic diseases.

To study genes that are specifically expressed in the eyes, we employed microarray and in situ hybridization analyses to identify and characterize differentially expressed ocular genes in eyeless masterblind (mbl-/-) zebrafish (Danio rerio). Among 70 differentially expressed genes in the mbl-/- mutant identified by microarray analysis, 8 down-regulated genes were characterized, including 4 eye-specific genes, opsin 1 short-wave-sensitive 1 (opn1sw1), crystallinbetaa1b (cryba1b), crystallinbetaa2b (cryba2b), and crystallingamma M2d3 (crygm2d3); 2 eye and brain genes, ATPase, H+ transporting, lysosomal, V0 subunit c (atp6v0c) and basic leucine zipper and W2 domains 1a (bzw1a); and 2 constitutive genes, heat shock protein 8 (hspa8) and ribosomal protein L7a (rpl7a). In situ hybridization experiments confirmed down-regulation of these 8 ocular formation genes in mbl-/- zebrafish and showed their ocular and dynamic temporal expression patterns during zebrafish early development. Further, an automated literature analysis of the 70 differentially expressed genes identified a sub-network of genes with known associations, either with each other or with ocular structures or development, and shows how this study contributes to the current body of knowledge.