Genomic organization of the CYP19b genes in the rainbow trout (Oncorhynchus mykiss Walbaum).
We report the occurrence of two CYP19b genes, namely CYP19b-I and CYP19b-II, encoding forms I and II of cytochrome P450aromB, the prevalently cerebral variant of aromatase in fish, in the nuclear genome of the rainbow trout. The CYP19b-I gene is 7.6 kbp-long, more than double the size of the known fish CYP19a and b genes, owing to the presence of three introns (1, 4 and 5) that enclose repeated sequences and are longer than 1 kbp. Unlike the CYP19a genes, but similarly to the CYP19b gene of the Nile tilapia, it contains 10, and not 9, exons, including an untranslated exon 1 (83 bp), as found also in the 5' non-coding region of mammalian CYP19 genes. The 5'-UTR is composed by exon 1 and the first 41 bp of exon 2 (150 bp), whose coding region covers the first 36 amino acid residues that incorporate the transmembrane domain. The CYP19b-II gene is only 2.5 kbp-long, because it contains only one intron, corresponding to the third intron of CYP19b-I, and lacks also its first two exons. Thus, it encodes for a presumably soluble protein. Apart from this difference, the rest of the coding region is virtually the same as that of the CYP19b-I gene. The 5'-UTR corresponds in part to the 3'-end (132 bp) of the second intron of the CYP19b-I gene, while the remaining portion (208 bp) bears no homology. CYP19b-II could be regarded as a pseudogene of the CYP19b-I gene, though it is unclear whether it is a processed or a duplicated pseudogene. Moreover, since it is transcriptionally active, it may retain a functional role for the overall brain aromatase activity in the rainbow trout.
Dalla Valle
L
L
Comparative Endocrinology Laboratory, Department of Biology, University of Padova, Via U. Bassi 58/B, 35131 Padova, Italy. luisadv@mail.bio.unipd.it
Toffolo
V
V
Vianello
S
S
Ikuo
Hirono
H
Takashi
Aoki
A
Belvedere
P
P
Colombo
L
L
D000818:Animals; D001141:Aromatase / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers; D005091:Exons / Q000235:genetics; D016678:Genome; D007438:Introns / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000235:genetics*
D017931:DNA Primers; D007527:Isoenzymes; D001141:Aromatase