Differential evolution of duplicated medakafish mitf genes

Molecular characterization, spatiotemporal expression, and background adaptation regulation of tyrosinase in loach (Misgurnus anguillicaudatus)

The Poyang Lake region is home to large-blackspot loaches (LBL), small-blackspot loaches (SBL), and non-blackspot loaches (NBL), Misgurnus anguillicaudatus. To investigate the impact of tyrosinase on spot development, the complementary DNAs (cDNA) of tyrosinase in M. anguillicaudatus (designated as Matyr) were cloned using the rapid amplification of cDNA ends (RACE)-PCR method. The full-length cDNA for Matyr was 2020 bp, and the open-reading frame comprised 1617 bp, encoding a predicted protein with 538 amino acids. Phylogenetic studies revealed that MaTyr was first grouped with Tyr of Triplophysa tibetana and Leptobotia taeniops, and then Tyr of other cyprinid fish. The quantitative reverse-transcription-PCR results show that Matyr was highly expressed in the muscle, caudal fin, and dorsal skin. The Matyr gene's messenger RNA expression pattern steadily increased from the fertilized ovum period to the somitogenesis period, and from the muscle effect stage to 6 days after fertilization, it considerably increased (p < 0.01). The Matyr hybridization signals with similar location could be found in all developmental stages of three kinds of loaches using whole-mount in situ hybridization (WISH) technology and were the strongest during the organ development period and melanin formation period. Dot hybridization signals in LBLs rapidly spread to the back of the body beginning at the period when the eyes first formed melanin, and their dimensions were larger than those of NBLs during the same time period. The body color of loaches could change reversibly with black/white background adaptation. The α-msh, mitfa, and tyr are mainly expressed in loaches adapted with a black background. Tyr gene could be involved in the development of blackspots and body color polymorphism, and contribute to organ development in the loach.

Adaptive phenotypic and genomic divergence in the common chaffinch (Fringilla coelebs) following niche expansion within a small oceanic island

According to models of ecological speciation, adaptation to adjacent, contrasting habitat types can lead to population divergence given strong enough environment-driven selection to counteract the homogenizing effect of gene flow. We tested this hypothesis in the common chaffinch (Fringilla coelebs) on the small island of La Palma, Canary Islands, where it occupies two markedly different habitats. Isotopic (δ13 C, δ15 N) analysis of feathers indicated that birds in the two habitats differed in ecosystem and/or diet, and analysis of phenotypic traits revealed significant differences in morphology and plumage colouration that are consistent with ecomorphological and ecogeographical predictions respectively. A genome-wide survey of single-nucleotide polymorphism revealed marked neutral structure that was consistent with geography and isolation by distance, suggesting low dispersal. In contrast, loci putatively under selection identified through genome-wide association and genotype-environment association analyses, revealed amarked adaptive divergence between birds in both habitats. Loci associated with phenotypic and environmental differences among habitats were distributed across the genome, as expected for polygenic traits involved in local adaptation. Our results suggest a strong role for habitat-driven local adaptation in population divergence in the chaffinches of La Palma, a process that appears to be facilitated by a strong reduction in effective dispersal distances despite the birds' high dispersal capacity.

Molecular and functional analysis of the microphthalmia-associated transcription factor (mitf) gene duplicates in red tilapia

In vertebrates, the microphthalmia-associated transcription factor (mitf) is at the hub of the melanin synthesis regulation network. However, little information is known about its molecular characterization, expression, location, or function in skin color differentiation and variation of red tilapia. The full-length cDNA sequences (1977 bp and 1999 bp) of mitfa and mitfb, encoding polypeptides of 491 and 514 amino acids, were effectively identified from red tilapia in this study. The Mitfa and Mitfb sequences of red tilapia clustered first with O. aureus, then with other teleost fish, according to phylogenetic analysis. Mitfa and mitfb mRNA were highly expressed in the brain, dorsal skin and eye tissues using quantitative real-time PCR. The mRNA expressions of mitfa and mitfb were the highest in the cleavage stage during the early development of red tilapia. Among three different colors of red tilapia, the expression levels of mitfa and mitfb were highest in the PB (pink with scattered black spots) dorsal skin. After overwintering, the mitfa and mitfb mRNA expressions were high in the dorsal skin of PB (color changed from pink to black). Mitfa and mitfb were mostly found in the epidermal layer of the dorsal skin, according to in situ hybridization (ISH) analysis. After injecting mitf-dsRNA duplicates along the tail vein of red tilapia, the activity of tyrosinase and the level of melanin in the dorsal skin both decreased significantly. The mRNA expressions of mitfa and its downstream genes (tyrb, tyrp1a and dct) decreased, whereas the mRNA expression of mitfb increased after mitfa-dsRNA injection. The mRNA expressions of mitfb, tyrb, tyrp1a and dct decreased, whereas the mRNA expression of mitfa increased after injecting mitfb-dsRNA. These findings suggest that mitf gene duplicates may play an important role in red tilapia skin color differentiation and variation via the melanogenesis pathway.

Medaka Oct4 is essential for pluripotency in blastula formation and ES cell derivation

The origin and evolution of molecular mechanisms underlying cellular pluripotency is a fundamental question in stem cell biology. The transcription factor Oct4 or Pou5f1 identified in mouse features pluripotency expression and activity in the inner cell mass and embryonic stem (ES) cells. Pou2 identified in zebrafish is the non-mammalian homolog prototype of mouse Oct4. The genes oct4 and pou2 have reportedly evolved by pou5 gene duplication in the common ancestor of vertebrates. Unlike mouse oct4, however, zebrafish pou2 lacks pluripotency expression and activity. Whether the presence of pluripotency expression and activity is specific for mammalian Oct4 or common to the ancestor of vertebrate Oct4 and Pou2 proteins has remained to be determined. Here we report that Oloct4, the medaka oct4/pou2, is essential for early embryogenesis and pluripotency maintenance. Oloct4 exists as a single copy gene and is orthologous to pou2 by sequence and chromosome synteny. Oloct4 expression occurs in early embryos, germ stem cells and ES cells like mouse oct4 but also in the brain and tail bud like zebrafish pou2. Importantly, OlOct4 depletion caused blastula lethality or blockage. We show that Oloct4 depletion abolishes ES cell derivation from midblastula embryos. Thus, Oloct4 has pluripotency expression and is essential for early embryogenesis and pluripotency maintenance. Our results demonstrate the conservation of pluripotency expression and activity in vertebrate Oct4 and Pou2 proteins. The finding that Oloct4 combines the features of mouse oct4 and zebrafish pou2 in expression and function suggests that Oloct4 might represent the ancestral prototype of vertebrate oct4 and pou2 genes.

Alternative splicing of the sheep MITF gene: novel transcripts detectable in skin

Microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factor, which regulates the differentiation and development of melanocytes and pigment cell-specific transcription of the melanogenesis enzyme genes. Though multiple splice variants of MITF have been reported in humans, mice and other vertebrate species, in merino sheep (Ovis aries), MITF gene splicing has not yet been investigated until now. To investigate the sheep MITF isoforms, the full length mRNA/cDNAs from the skin of merino sheep were cloned, sequenced and characterized. Reverse transcriptase (RT)-PCR analysis and molecular prediction revealed two basic splice variants with (+) and without (-) an 18 bp insertion viz. CGTGTATTTTCCCCACAG, in the coding region (CDS) for the amino acids 'ACIFPT'. It was further confirmed by the complete nucleotide sequencing of splice junction covering intron-6 (2463 bp), wherein an 18bp intronic sequence is retained into the CDS of MITF (+) isoform. Further, full-length cDNA libraries were enriched by the method of 5' and 3' rapid amplification of cDNA ends (RACE-PCR). A total of seven sheep MITF splice variants, with distinct N-terminus sequences such as MITF-A, B, E, H, and M, the counterparts of human and mouse MITF, were identified by 5' RACE. The other two 5' RACE products were found to be novel splice variants of MITF and represented as 'MITF truncated form (Trn)-1, 2'. These alternative splice (AS) variants were illustrated using comparative genome analysis. By means of 3' RACE three different MITF 3' UTRs (625, 1083, 3167bp) were identified and characterized. We also demonstrated that the MITF gene expression determined at transcript level is mediated via an intron-6 splicing event. Here we summarize for the first time, the expression of seven MITF splice variants with three distinct 3' UTRs in the skin of merino sheep. Our data refine the structure of the MITF gene in sheep beyond what was previously known in humans, mice, dogs and other mammals.

Alternative transcription generates multiple Mitf isoforms with different expression patterns and activities in medaka

Microphthalmia-associated transcription factor (Mitf) is best known for distinct functions in multiple cell lineages including melanocytes, mast cells, and osteoclasts. In mammals, mitf produces multiple Mitf isoforms by alternative transcription and splicing. The fish medaka has two mitf genes, mitf1 and mitf2. Here, we report differential expression and activities of medaka Mitf isoforms. Molecular cloning identified four mitf1 variants encoding isoforms Mitf1A, MitfB, MitfH, and MitfM, and only one mitf2RNA encoding Mitf2M, which exhibited differential expression. Mitf1 isoforms and Mitf2M differed dramatically in activating the dazl and tyrosinase promoters DAZ and TYR. Interestingly, Mitf1ΔN, an N-terminus-less Mitf1 mutant form, retained activity to activate TYR but not DAZ. Importantly, Mitf1B was also sufficient for inducing melanocyte differentiation and endogenous tyrosinase RNA expression in medaka embryonic stem cells. Intriguingly, Mitf1 isoforms possessed considerable differences in inducing the expression of multiple cell lineage marker genes. Therefore, alternative mitf transcription is a conserved mechanism from fish to mammals, and medaka Mitf1 isoforms show differences in expression and activity. We conclude that differential expression of isoforms contributes to multiple distinct functions of Mitf in vertebrates.