Pigment cell lineage-specific expression activity of the ascidian tyrosinase-related gene

An examination of melanogenic traits and <i>TYRP1</i> polymorphism in Nanping and Romney Marsh sheep breeds

Abstract. The effects of mutations of the gene for tyrosinase-related protein 1 (TYRP1) on the black muscles and coat color in Nanping black-boned sheep were investigated. Tyrosinase activity and melanin content in plasma were measured and compared in three random groups of sheep: Nanping black-boned (101 heads), Nanping normal (106 heads) and Romney Marsh sheep (82 heads, Ovis aries). Eight exons and their partial flanking regions of the TYRP1 gene were amplified. Six intronic mutations and six exonic polymorphisms including two non-synonymous mutations [c.203C > T (p.A68V) and c.1202T > C (p.V401A)] were identified. Using a bi-directional polymerase chain reaction allele-specific amplification (bi-PASA) of the mutation c.203C > T it was shown that the frequencies of allele C in the Nanping black-boned, Nanping normal and Romney Marsh sheep were respectively 0.955, 0.967 and 0.744. For the mutation c.1202T > C, the frequencies of allele T in the three populations of sheep were respectively 0.777, 0.745 and 0.793 as measured using the single-strand conformation polymorphism. When the data from sheep of all three populations with the CC genotype of SNP c.203C > T were pooled, it was found that there was significantly higher (P < 0.05) tyrosinase activity, content of alkali-soluble melanin and ratio of eumelanin : total melanin than in the plasma of sheep with the CT and TT genotypes. This was not so within each of the three groups of sheep. No significant effect of the TRYP1 genotype on coat color was found. Further studies will be necessary to determine the cause of the black traits in Nanping black-boned sheep.

Microinjection of Exogenous DNA into Eggs of Halocynthia roretzi

Exogenous gene expression assays during development, including reporters under the control of 5' upstream enhancer regions of genes, constitute a powerful technique for understanding the mechanisms of tissue-specific gene expression regulation and determining the characteristics, behaviors, and functions of cells that express these genes. The simple marine chordate Halocynthia roretzi has been used for these transgenic analyses for a long time and is an excellent model system for such studies, especially in comparative analyses with other ascidians. In this study, I describe simple methods for microinjecting H. roretzi eggs with exogenous DNA, such as a promoter construct consisting of a 5' upstream region and a reporter gene, which are prerequisites for transgenic analyses. I also describe basic knowledge regarding this ascidian species, providing reasons why it is an ideal subject for developmental biology studies.

New insights into the evolution of metazoan tyrosinase gene family

Tyrosinases, widely distributed among animals, plants and fungi, are involved in the biosynthesis of melanin, a pigment that has been exploited, in the course of evolution, to serve different functions. We conducted a deep evolutionary analysis of tyrosinase family amongst metazoa, thanks to the availability of new sequenced genomes, assessing that tyrosinases (tyr) represent a distinctive feature of all the organisms included in our study and, interestingly, they show an independent expansion in most of the analyzed phyla. Tyrosinase-related proteins (tyrp), which derive from tyr but show distinct key residues in the catalytic domain, constitute an invention of chordate lineage. In addition we here reported a detailed study of the expression territories of the ascidian Ciona intestinalis tyr and tyrps. Furthermore, we put efforts in the identification of the regulatory sequences responsible for their expression in pigment cell lineage. Collectively, the results reported here enlarge our knowledge about the tyrosinase gene family as valuable resource for understanding the genetic components involved in pigment cells evolution and development.

FGF/MAPK/Ets signaling renders pigment cell precursors competent to respond to Wnt signal by directly controlling Ci-Tcf transcription

FGF and Wnt pathways constitute two fundamental signaling cascades, which appear to crosstalk in cooperative or antagonistic fashions in several developmental processes. In vertebrates, both cascades are involved in pigment cell development, but the possible interplay between FGF and Wnt remains to be elucidated. In this study, we have investigated the role of FGF and Wnt signaling in development of the pigment cells in the sensory organs of C. intestinalis. This species possesses the basic features of an ancestral chordate, thus sharing conserved molecular developmental mechanisms with vertebrates. Chemical and targeted perturbation approaches revealed that a FGF signal, spreading in time from early gastrulation to neural tube closure, is responsible for pigment cell precursor induction. This signal is transmitted via the MAPK pathway, which activates the Ci-Ets1/2 transcription factor. Targeted perturbation of Ci-TCF, a downstream factor of the canonical Wnt pathway, indicated its contribution to pigment cell differentiation Furthermore, analyses of the Ci-Tcf regulatory region revealed the involvement of the FGF effector, Ci-Ets1/2, in Ci-Tcf transcriptional regulation in pigment cell precursors. Our results indicate that both FGF and the canonical Wnt pathways are involved in C. intestinalis pigment cell induction and differentiation. Moreover, we present a case of direct transcriptional regulation exerted by the FGF signaling cascade, via the MAPK-ERK-Ets1/2, on the Wnt downstream gene Ci-Tcf. Several examples of FGF/Wnt signaling crosstalk have been described in different developmental processes; however, to our knowledge, FGF-Wnt cross-interaction at the transcriptional level has never been previously reported. These findings further contribute to clarifying the multitude of FGF-Wnt pathway interactions.

Eye evolution: common use and independent recruitment of genetic components

Animal eyes can vary in complexity ranging from a single photoreceptor cell shaded by a pigment cell to elaborate arrays of these basic units, which allow image formation in compound eyes of insects or camera-type eyes of vertebrates. The evolution of the eye requires involvement of several distinct components-photoreceptors, screening pigment and genes orchestrating their proper temporal and spatial organization. Analysis of particular genetic and biochemical components shows that many evolutionary processes have participated in eye evolution. Multiple examples of co-option of crystallins, Galpha protein subunits and screening pigments contrast with the conserved role of opsins and a set of transcription factors governing eye development in distantly related animal phyla. The direct regulation of essential photoreceptor genes by these factors suggests that this regulatory relationship might have been already established in the ancestral photoreceptor cell.

Decoding cis-regulatory systems in ascidians

Ascidians, or sea squirts, are lower chordates, and share basic gene repertoires and many characteristics, both developmental and physiological, with vertebrates. Therefore, decoding cis-regulatory systems in ascidians will contribute toward elucidating the genetic regulatory systems underlying the developmental and physiological processes of vertebrates. cis-Regulatory DNAs can also be used for tissue-specific genetic manipulation, a powerful tool for studying ascidian development and physiology. Because the ascidian genome is compact compared with vertebrate genomes, both intergenic regions and introns are relatively small in ascidians. Short upstream intergenic regions contain a complete set of cis-regulatory elements for spatially regulated expression of a majority of ascidian genes. These features of the ascidian genome are a great advantage in identifying cis-regulatory sequences and in analyzing their functions. Function of cis-regulatory DNAs has been analyzed for a number of tissue-specific and developmentally regulated genes of ascidians by introducing promoter-reporter fusion constructs into ascidian embryos. The availability of the whole genome sequences of the two Ciona species, Ciona intestinalis and Ciona savignyi, facilitates comparative genomics approaches to identify cis-regulatory DNAs. Recent studies demonstrate that computational methods can help identify cis-regulatory elements in the ascidian genome. This review presents a comprehensive list of ascidian genes whose cis-regulatory regions have been subjected to functional analysis, and highlights the recent advances in bioinformatics and comparative genomics approaches to cis-regulatory systems in ascidians.