6533b82efe1ef96bd1293bde

RESEARCH PRODUCT

The amphibian globin gene repertoire as revealed by the <i>Xenopus </i>genome

subject

description

The draft genome sequence of the Western clawed frog <i>Xenopus (Silurana) tropicalis</i> facilitates the identification, expression analysis and phylogenetic classification of the amphibian globin gene repertoire. Frog and mammalian neuroglobin display about 67% protein sequence identity, with the expected predominant expression in frog brain and eye. Frog and mammalian cytoglobins share about 69% of their amino acids, but the frog protein lacks the mammalian-type extension at the C-terminus. Like in mammals, <i>X. tropicalis</i> cytoglobin is expressed in many organs including neural tissue. Neuroglobin and cytoglobin genomic regions are syntenically conserved in all vertebrate classes. Frog and fish globin X show only 57% amino acid identity, but gene synteny analysis confirms orthology. The expression pattern of <i>X. laevis</i> globin X differs from that in fish, with a prominent expression in the eye and weak expression in most other examined tissues. Globin X is possibly present as two paralogous copies in <i>X. tropicalis</i>, with one copy showing transition stages of non-functionalization. The amphibian genome contains a previously unknown globin type (tentatively named ‘globin Y’) which is expressed in a broad range of tissues and is distantly related to the cytoglobin lineage. The globin Y gene is linked to a cluster of larval and adult hemoglobin α and β genes which contains substantially more paralogous hemoglobin gene copies than previously published. Database and gene synteny analyses confirm the absence of a myoglobin gene in <i>X. tropicalis</i>.