Genomic analysis has upended chordate phylogeny, placing the tunicates as the sister group to the vertebrates. This taxonomic rearrangement raises questions about the emergence of a tunicate/vertebrate ancestor. Characterization of developmental genes uniquely shared by tunicates and vertebrates is one promising approach for deciphering developmental shifts underlying acquisition of novel, ancestral traits. The matrix glycoprotein Fibronectin (FN) has long been considered a vertebrate-specific gene, playing a major instructive role in vertebrate embryonic development. However, the recent computational prediction of an orthologous "vertebrate-like" Fn gene in the genome of a tunicate, Ciona savignyi, challenges this viewpoint suggesting that Fn may have arisen in the shared tunicate/vertebrate ancestor. Here we verify the presence of a tunicate Fn ortholog. Transgenic reporter analysis was used to characterize a Ciona Fn enhancer driving expression in the notochord. Targeted knockdown in the notochord lineage indicates that FN is required for proper convergent extension. These findings suggest that acquisition of Fn was associated with altered notochord morphogenesis in the vertebrate/tunicate ancestor.
Additional file 1: Table 2. Exon Lengths and Splice Phases in the CinFN gene. Exon length and splice phases of the CinFN gene were estimated by BLAT nucleotide searches of the C. intestinalis genome (Joint Genome Institute v2.0) with the UCSC Genome Browser. Exons are color-coded according to their splice phases.
The dark-like (dal) mutant mouse has a pleiotropic phenotype that includes dark dorsal hairs and reproductive degeneration. Their pigmentation phenotype is similar to Attractin (Atrn) mutants, which also develop vacuoles throughout the brain. In further characterizing the testicular degeneration of dal mutant males, we found that they had reduced serum testosterone and developed vacuoles in their testes. Genetic crosses placed dal upstream of the melanocortin 1 receptor (Mc1r) and downstream of agouti, although dal suppressed the effect of agouti on pigmentation but not body weight. Atrn(mg-3J) and dal showed additive effects on pigmentation, testicular vacuolation, and spongiform neurodegeneration, but transgenic overexpression of Attractin-like-1 (Atrnl1), which compensates for loss of ATRN, did not rescue dal mutant phenotypes. Our results suggest dal and Atrn function in the same pathway and that identification of the dal gene will provide insight into molecular mechanisms of vacuolation in multiple cell types.
Additional file 4: Table 5. Estimates of Evolutionary Divergence between FN Sequences. Evolutionary divergence between tunicate and vertebrate FN protein sequences was calculated in MEGA6 as the number of amino acid differences per site from between sequences. Pairwise differences are shown below the diagonal, and analytical standard error estimates above the diagonal. The analysis involved 11 amino acid sequences with 4516 positions. All ambiguous positions were removed for each sequence pair.
Summary Mutations in mouse Mahogunin Ring Finger‐1 ( Mgrn1 ) were first recognized for their effect on agouti‐mediated pigment‐type switching. Mgrn1 null mutants are completely black and develop spongiform degeneration of the brain. Mgrn1 hypomorphs have dark fur but do not develop neurodegeneration. We characterized a new Mgrn1 hypomorphic allele caused by a gene‐trap insertion. Mice homozygous for this mutation are slightly darker than non‐mutant animals. They show reduced overall expression of Mgrn1 and two of the four normal Mgrn1 isoforms are replaced by β ‐GEO fusion proteins that differ from the normal proteins at their carboxy termini. To investigate the role of different Mgrn1 isoforms in pigment‐type switching, we used quantitative relative reverse transcriptase polymerase chain reaction to examine their expression in the skin of Mgrn1 mutant and control mice. Most Mgrn1 mutants produce little or no normal Mgrn1 in the skin. Mgrn1 null mutant mice overexpressing isoform I or III, which are normally absent or weakly expressed in adult skin, had normal agouti‐banded hairs. Our results indicate that reduced levels of MGRN1 cause the pigmentation phenotypes of Mgrn1 mutant mice and that there are no significant differences in the function of the four MGRN1 isoforms in pigment‐type switching.
DDX11 is a DNA helicase of the conserved FANCJ/RAD3/XPD family involved in maintaining genome stability. Studies in yeast and humans have shown requirements for DDX11 in sister chromatid cohesion and DNA repair. In mouse, loss of Ddx11 results in embryonic lethality. However, the developmental defects of Ddx11 mutants are poorly understood.We describe the characterization and positional cloning of cetus, a mouse ENU-induced mutation in Ddx11. We demonstrate that cetus causes a nonconservative amino acid change in DDX11 motif V and that this mutation is a null allele of Ddx11. cetus mutant embryos failed to thrive beyond embryonic day 8.5 and displayed placental defects similar to those described in Ddx11 null embryos. Additionally, our characterization of Ddx11(cetus) mutants identified embryonic phenotypes that had not been previously reported in Ddx11(KO) embryos, including loss of somitic mesoderm, an open kinked neural tube and abnormal heart looping. We show that loss of Ddx11 causes widespread apoptosis from early embryonic stages and that loss of Ddx11 disrupts somitic mesoderm more dramatically than other embryonic cells.Our results identify novel roles of Ddx11 during embryo morphogenesis and demonstrate that the activity of its motif V is essential for DDX11 function.
