Use of chimeras to study gene function in mesodermal tissues during gastrulation and early organogenesis

Transcriptomic Analysis of Induced Pluripotent Stem Cells Derived from Patients with Bipolar Disorder from an Old Order Amish Pedigree

Fibroblasts from patients with Type I bipolar disorder (BPD) and their unaffected siblings were obtained from an Old Order Amish pedigree with a high incidence of BPD and reprogrammed to induced pluripotent stem cells (iPSCs). Established iPSCs were subsequently differentiated into neuroprogenitors (NPs) and then to neurons. Transcriptomic microarray analysis was conducted on RNA samples from iPSCs, NPs and neurons matured in culture for either 2 weeks (termed early neurons, E) or 4 weeks (termed late neurons, L). Global RNA profiling indicated that BPD and control iPSCs differentiated into NPs and neurons at a similar rate, enabling studies of differentially expressed genes in neurons from controls and BPD cases. Significant disease-associated differences in gene expression were observed only in L neurons. Specifically, 328 genes were differentially expressed between BPD and control L neurons including GAD1, glutamate decarboxylase 1 (2.5 fold) and SCN4B, the voltage gated type IV sodium channel beta subunit (-14.6 fold). Quantitative RT-PCR confirmed the up-regulation of GAD1 in BPD compared to control L neurons. Gene Ontology, GeneGo and Ingenuity Pathway Analysis of differentially regulated genes in L neurons suggest that alterations in RNA biosynthesis and metabolism, protein trafficking as well as receptor signaling pathways may play an important role in the pathophysiology of BPD.

Mouse gastrulation: the formation of a mammalian body plan

The process of gastrulation is a pivotal step in the formation of the vertebrate body plan. The primary function of gastrulation is the correct placement of precursor tissues for subsequent morphogenesis. There is now mounting evidence that the body plan is established through inductive interactions between germ layer tissues and by the global patterning activity emanating from embryonic organizers. An increasing number of mouse mutants have been described that have gastrulation defects, providing important insights into the molecular mechanisms that regulate this complex process. In this review, we explore the mouse embryo before and during gastrulation, highlighting its similarities with other vertebrate embryos and its unique characteristics.

fgfr-1 is required for embryonic growth and mesodermal patterning during mouse gastrulation

Experiments in amphibians have implicated fibroblast growth factors (FGFs) in the generation and patterning of mesoderm during embryogenesis. We have mutated the gene for fibroblast growth factor receptor 1 (fgfr-1) in the mouse to genetically dissect the role of FGF signaling during development. In the absence of fgfr-1 signaling, embryos displayed early growth defects; however, they remained capable of gastrulating and generating mesoderm. The nascent mesoderm of fgfr-1 homozygous mutant embryos differentiated into diverse mesodermal subtypes, but mesodermal patterning was aberrant. Somites were never generated and axial mesoderm was greatly expanded at the expense of paraxial mesoderm. These results suggest that FGFR-1 transduces signals that specify mesodermal cell fates and regional patterning of the mesoderm during gastrulation.