Nkx2.5 is involved in myeloid cell differentiation at anterior ventral blood islands in the Xenopus embryo

Noggin proteins are multifunctional extracellular regulators of cell signalling

Noggin is an extracellular cysteine knot protein that plays a crucial role in vertebrate dorsoventral patterning. Noggin binds and inhibits the activity of bone morphogenetic proteins via a conserved N-terminal clip domain. Noncanonical orthologs of Noggin that lack a clip domain (“Noggin-like” proteins) are encoded in many arthropod genomes and are thought to have evolved into receptor tyrosine kinase ligands that promote Torso/receptor tyrosine kinase signaling rather than inhibiting bone morphogenic protein signaling. Here, we examined the molecular function of noggin/noggin-like genes (ApNL1 and ApNL2) from the arthropod pea aphid using the dorso-ventral patterning of Xenopus and the terminal patterning system of Drosophila to identify whether these proteins function as bone morphogenic protein or receptor tyrosine kinase signaling regulators. Our findings reveal that ApNL1 from the pea aphid can regulate both bone morphogenic protein and receptor tyrosine kinase signaling pathways, and unexpectedly, that the clip domain is not essential for its antagonism of bone morphogenic protein signaling. Our findings indicate that ancestral noggin/noggin-like genes were multifunctional regulators of signaling that have specialized to regulate multiple cell signaling pathways during the evolution of animals.

Zebrafish foxc1a controls ventricular chamber maturation by directly regulating wwtr1 and nkx2.5 expression

Chamber maturation is a significant process in cardiac development. Disorders of this crucial process lead to a range of congenital heart defects. Foxc1a is a critical transcription factor reported to regulate the specification of cardiac progenitor cells. However, little is known about the role of Foxc1a in modulating chamber maturation. Previously, we reported that foxc1a-null zebrafish embryos exhibit disrupted heart structures and functions. In this study, we observed that ventricle structure and cardiomyocyte proliferation were abolished during chamber maturation in foxc1a-null zebrafish embryos. To observe the endogenous localization of Foxc1a in the hearts of living embryos, we inserted eyfp at the foxc1a genomic locus using TALEN. Analysis of the knockin zebrafish showed that foxc1a was widely expressed in ventricular cardiomyocytes during chamber development. Cardiac RNA sequencing analysis revealed downregulated expression of the Hippo signaling effector wwtr1. Dual-luciferase and chromatin immunoprecipitation assays revealed that Foxc1a could bind directly to three sites in the wwtr1 promoter region. Furthermore, wwtr1 mRNA overexpression was sufficient to reverse the ventricle defects during chamber maturation. Conditional overexpression of nkx2.5 also partially rescued the ventricular defects during chamber development. These findings demonstrate that wwtr1 and nkx2.5 are direct targets of Foxc1a during ventricular chamber maturation.

Multiple origins of embryonic and tadpole myeloid cells in Xenopus laevis

Rabbit anti-serum against a myeloid-cell-specific peroxidase (Mpo) of Xenopus laevis was generated to identify myeloid cells in adult and larval animals. Smears of blood samples from adult hematopoietic organs were co-stained with Mpo and with XL-2, a mouse monoclonal antibody against a leukocyte common antigen. Lymphocytes found in the thymus and spleen were XL-2⁺Mpo^- and granulocytes found in peripheral blood cells and the spleen were XL-2⁺Mpo⁺, indicating that double-staining with these two antibodies allowed classification of the leukocyte lineages. Immunohistochemical analysis of larval organs showed that XL-2⁺Mpo^- cells were scattered throughout the liver, whereas XL-2⁺Mpo⁺ cells were present mainly in the cortex region. Interestingly, a cluster of XL-2⁺Mpo⁺ cells was found in the region of the larval mesonephric rudiment. The ratio of XL-2⁺Mpo⁺ cells to XL-2⁺ cells in the mesonephric region was approximately 80%, which was much higher than that found in other hematopoietic organs. In order to elucidate the embryonic origin of the myeloid cells in the tadpole mesonephros, grafting experiments between X. laevis and X. borealis embryos were performed to trace the X. borealis cells as donor cells. Among the embryonic tissues examined, the tailbud tissue at the early neurula stage contributed greatly to the myeloid cluster in the mesonephric region at stage 48. Therefore, at least four independent origins of the myeloid cell population can be traced in the Xenopus embryo.

Negative Glucocorticoid Response-Like Element from the First Intron of the Chicken Growth Hormone Gene Represses Gene Expression in the Rat Pituitary Tumor Cell Line

The effects of introns, especially the first intron, on the regulation of gene expression remains unclear. Therefore, the objective of the present study was to investigate the transcriptional regulatory function of intron 1 on the chicken growth hormone (cGH) gene in the rat pituitary tumor cell line (GH4-C1). Transient transfection using first-intron-inserted cGH complete coding sequences (CDSs) and non-intron-inserted cGH CDS plasmids, quantitative RT-PCR (qRT-PCR) and western blot assays were used to detect the expression of cGH. The reporter gene assay was also used to investigate the effect of a series of fragments in the first intron of cGH on gene expression in GH4-C1. All of the results revealed that a 200-bp fragment located in the +485/+684 region of intron 1 was essential for repressing the expression of cGH. Further informatics analysis showed that there was a cluster of 13 transcriptional factor binding sites (TFBSs) in the +485/+684 region of the cGH intron 1. Disruption of a glucocorticoid response-like element (the 19-nucleotide sequence 5'-AGGCTTGACAGTGACCTCC-3') containing a T-box motif (TGACCT) located within this DNA fragment increased the expression of the reporter gene in GH4-C1. In addition, an electrophoretic mobility shift assay (EMSA) revealed a glucocorticoid receptor (GR) protein of rat binding to the glucocorticoid response-like element. Together, these results indicate that there is a negative glucocorticoid response-like element (nGRE) located in the +591/+609 region within the first intron of cGH, which is essential for the down-regulation of cGH expression.