Zebra fish myc family and max genes: differential expression and oncogenic activity throughout vertebrate evolution

Two c-myc genes from a tetraploid fish, the common carp (Cyprinus carpio)

Two c-myc genes have been isolated from a tetraploid fish, the common carp (Cyprinus carpio). The nucleotide (nt) sequences of the two genes and their flanking regions (CAM1, 8675 bp and CAM2, 5784 bp) have been determined. Both genes contain two coding exons which are homologs of c-myc exons 2 and 3 in higher vertebrates. The nt sequence homologous to c-myc exon 1 of higher vertebrates has not been found. Carp CAM1 and CAM2 presumably encode peptides of 394 and 401 amino acids (aa), respectively. These two peptides share 55-91% aa identity with those of humans, chickens, frog, rainbow trout and zebra fish. The two carp c-Myc have a Glu stretch at the beginning region of exon 3. This Glu stretch is also present in zebra fish, suggesting that it may be characteristic to c-myc genes of cyprinid fishes. The existence of two c-myc in carp is attributed to the tetraploid nature of carp. These two genes share 92.4% nt identity in the coding region and 84.2% in the intron. The two deduced peptides share 94.2% aa identity, suggesting that the tetraploid event probably occurred 58 million years ago. Both of the genes' cDNA clones were obtained from a cDNA library of carp peripheral blood leukocytes, implying that both of the genes are expressed.

Involvement of wnt1 and pax2 in the formation of the midbrain-hindbrain boundary in the zebrafish gastrula

The secreted signalling molecule encoded by the wnt1 gene and the paired box-containing pax2 gene are thought to play an integral role in patterning the zebrafish rostral nervous system. Using a double-label analysis, we compare the expression patterns of wnt1 RNA and pax2 protein during zebrafish embryogenesis to determine whether they were expressed in identical or overlapping patterns in individual embryos. During gastrulation, wnt1 RNA was detected in a pattern similar but not identical to the pax2 protein. Later, wnt1 and pax2 co-localize to the midbrain-hindbrain boundary. Exogenous retinoic acid, a teratogen that is known to affect the formation of the midbrain-hindbrain boundary, has a profound affect on both wnt1 and pax2 expression at gastrulation. Furthermore, when pax2 is overexpressed in zebrafish embryos, the wnt1 pattern of expression expands ventrally in the prospective rostral neuroepithelium. Despite the widespread and random distribution of exogenous pax2 RNA, it alone is unable to induce wnt1 expression in other ectopic sites. These results are consistent with the coordinate expression of wnt1 and pax2 being in a pathway responsible for establishing the midbrain-hindbrain boundary and support the earlier interpretation that pax2 may regulate wnt1 expression [Krauss et al., 1992], although only in a subset of embryonic cells. These data suggest that a predisposition for the regionalization of the central nervous system exists at gastrulation.