Expression of a novel Ski-like gene in Xenopus development

Epigenetic signature of very low birth weight in young adult life

BACKGROUND

Globally, one in ten babies is born preterm (<37 weeks), and 1-2% preterm at very low birth weight (VLBW, <1500 g). As adults, they are at increased risk for a plethora of health conditions, e.g., cardiometabolic disease, which may partly be mediated by epigenetic regulation. We compared blood DNA methylation between young adults born at VLBW and controls.

METHODS

157 subjects born at VLBW and 161 controls born at term, from the Helsinki Study of Very Low Birth Weight Adults, were assessed for peripheral venous blood DNA methylation levels at mean age of 22 years. Significant CpG-sites (5'-C-phosphate-G-3') were meta-analyzed against continuous birth weight in four independent cohorts (pooled n = 2235) with cohort mean ages varying from 0 to 31 years.

RESULTS

In the discovery cohort, 66 CpG-sites were differentially methylated between VLBW adults and controls. Top hits were located in HIF3A, EBF4, and an intergenic region nearest to GLI2 (distance 57,533 bp). Five CpG-sites, all in proximity to GLI2, were hypermethylated in VLBW and associated with lower birth weight in the meta-analysis.

CONCLUSION

We identified differentially methylated CpG-sites suggesting an epigenetic signature of preterm birth at VLBW present in adult life.

IMPACT

Being born preterm at very low birth weight has major implications for later health and chronic disease risk factors. The mechanism linking preterm birth to later outcomes remains unknown. Our cohort study of 157 very low birth weight adults and 161 controls found 66 differentially methylated sites at mean age of 22 years. Our findings suggest an epigenetic mark of preterm birth present in adulthood, which opens up opportunities for mechanistic studies.

RARγ is required for mesodermal gene expression prior to gastrulation in Xenopus

The developing vertebrate embryo is exquisitely sensitive to retinoic acid (RA) concentration, particularly during anteroposterior patterning. In contrast to Nodal and Wnt signaling, RA was not previously considered to be an instructive signal in mesoderm formation during gastrulation. Here, we show in Xenopus that RARγ is indispensable for the expression of early mesoderm markers and is, therefore, an obligatory factor in mesodermal competence and/or maintenance. We identified several novel targets upregulated by RA receptor signaling in the early gastrula that are expressed in the circumblastoporal ring and linked to mesodermal development. Despite overlapping expression patterns of the genes encoding the RA-synthesizing enzyme Aldh1a2 and the RA-degrading enzyme Cyp26a1, RARγ1 functions as a transcriptional activator in early mesoderm development, suggesting that RA ligand is available to the embryo earlier than previously appreciated. RARγ1 is required for cellular adhesion, as revealed by spontaneous dissociation and depletion of ncam1 mRNA in animal caps harvested from RARγ1 knockdown embryos. RARγ1 knockdown obliterates somite boundaries, and causes loss of Myod protein in the presomitic mesoderm, but ectopic, persistent expression of Myod protein in the trunk. Thus, RARγ1 is required for stabilizing the mesodermal fate, myogenic commitment, somite boundary formation, and terminal skeletal muscle differentiation.

Regulation of early xenopus embryogenesis by Smad ubiquitination regulatory factor 2

BACKGROUND

Smad ubiquitination regulatory factor (Smurf) 1 and 2 are E3 ubiquitin ligases originally identified as inhibitors of transforming growth factor beta signaling and are shown to modulate multiple cellular activities. The roles of Smurfs in vertebrate embryogenesis, however, are not completely understood.

RESULTS

Here we investigate the function of Smurf2 during early Xenopus development. We show that distinctly from Smurf1, overexpression of Smurf2 in presumptive mesoderm interfered with mesoderm induction and caused axial defects, whereas knockdown of Smurf2 with antisense morpholino oligonucleotides resulted in expansion of the mesoderm. These results imply that Smurf2 may modulate nodal-mediated mesodermal induction. Consistently, ventral expression of Smurf2 induced a partial secondary axis with head structures. In the ectoderm, Smurf2 resembled Smurf1 in controlling neural and epidermal marker expression and influencing head formation. Smurf1, but not Smurf2, additionally affected neural tube closure. Interestingly, both Smurfs could enhance as well as repress neural crest markers, implying that they modulate their targets dynamically during neural plate border specification.

CONCLUSION

Our data demonstrate that Smurf1 and Smurf2 have overlapping and distinct functionalities during early frog embryogenesis; collectively, they regulate ectodermal and mesodermal induction and patterning to ensure normal development of Xenopus embryos.

Genetic defects of human brain development

This review focuses on malformations of the central nervous system that have a genetic etiology. One can view each malformation as giving us unique details on a map entitled "how to make a human brain." The gene(s) that cause each malformation are being identified, allowing discovery of their specific role in neurodevelopment, and defining a "road" on the map. The malformation is then the developmental consequence of "taking a wrong turn." Assimilation of complementary data from other species with human malformation phenotype and genotype is revealing just how wonderful and complex the neurodevelopment map is. Here we highlight recent research on brain malformations and how this is illuminating the map of normal human brain formation.