SIP1 Mediates Cell-Fate Decisions between Neuroectoderm and Mesendoderm in Human Pluripotent Stem Cells

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Highlights? Smad-interacting protein 1 (SIP1) regulates hESC differentiation ? SIP1 upregulation promotes neuroectodermal differentiation ? SIP1 inhibits mesendodermal and endodermal differentiation ? SMAD2/3 and NANOG/OCT4/SOX2 cooperatively regulate SIP1 expression     

Totipotent migratory stem cells in a hydroid

Hydroids, members of the most ancient eumetazoan phylum, the Cnidaria, harbor multipotent, migratory stem cells lodged in interstitial spaces of epithelial cells and are therefore referred to as interstitial cells or i-cells. According to traditional understanding, based on studies in Hydra, these i-cells give rise to several cell types such as stinging cells, nerve cells, and germ cells, but not to ectodermal and endodermal epithelial cells; these are considered to constitute separate cell lineages. We show here that, in Hydractinia, the developmental potential of these migratory stem cells is wider than previously anticipated. We eliminated the i-cells from subcloned wild-type animals and subsequently introduced i-cells from mutant clones and vice versa. The mutant donors and the wild-type recipients differed in their sex, growth pattern, and morphology. With time, the recipient underwent a complete conversion into the phenotype and genotype of the donor. Thus, under these experimental conditions the interstitial stem cells of Hydractinia exhibit totipotency.     

Comparative phylogenetic analysis of the evolution of semelparity and life history in salmonid fishes

The selective pressures involved in the evolution of semelparity and its associated life-history traits are largely unknown. We used species-level analyses, independent contrasts, and reconstruction of ancestral states to study the evolution of body length, fecundity, egg weight, gonadosomatic index, and parity (semelparity vs. degree of iteroparity) in females of 12 species of salmonid fishes. According to both species-level analysis and independent contrasts analysis, body length was positively correlated with fecundity, egg weight, and gonadosomatic index, and semelparous species exhibited a significantly steeper slope for the regression of egg weight on body length than did iteroparous species. Percent repeat breeding (degree of iteroparity) was negatively correlated with gonadosomatic index using independent contrasts analysis. Semelparous species had significantly larger eggs by species-level analysis, and the egg weight contrast for the branch on which semelparity was inferred to have originated was significantly larger than the other egg weight contrasts, corresponding to a remarkable increase in egg weight. Reconstruction of ancestral states showed that egg weight and body length apparently increased with the origin of semelparity, but fecundity and gonadosomatic index remained more or less constant or decreased. Thus, the strong evolutionary linkages between body size, fecundity, and gonadosomatic index were broken during the transition from iteroparity to semelparity. These findings suggest that long-distance migrations, which increase adult mortality between breeding episodes, may have been necessary for the origin of semelparity in Pacific salmon, but that increased egg weight, leading to increased juvenile survivorship, was crucial in driving the transition. Our analyses support the life-history hypotheses that a lower degree of repeat breeding is linked to higher reproductive investment per breeding episode, and that semelparity evolves under a combination of relatively high juvenile survivorship and relatively low adult survivorship.     

Structural characterization of Escherichia coli sialic acid synthase

Wnt-1, the vertebrate counterpart of the Drosophila wingless gene, plays an important role in the early morphogenesis of neural tissues. In this report, we have shown that overexpression of Wnt-1 can direct embryonic carcinoma P19 cells to differentiate into neuron-like cells in the absence of retinoic acid. Immunocytochemistry showed that these cells expressed neuronal markers, such as the neurofilament (NF) and microtubule-associated protein 2 (MAP2), but failed to express the glial cell marker, glial fibrillary acidic protein (GFAP). RT-PCR revealed that two basic helix-loop-helix (bHLH) genes, Mash-1 and Ngn-1, were up-regulated during the differentiation stage of Wnt-1-overexpressing P19 cells. These results suggest that the Wnt-1 gene promotes neuronal differentiation and inhibits gliogenesis during the neural differentiation of P19 cells, and that neural bHLH genes might be involved in this process.     

The damselfishes (Pisces: Osteichthyes: Pomacentridae) of Peninsular Malaysia and Singapore: systematics,ecology and conservation

Damselfishes (Pomacentridae) are among the most common of reef fishes in tropical seas, comprising 320 species in all, with 268 species alone in the Indo-West Pacific regions. 15 genera (Abudefduf, Amblyglyphidodon, Amphiprion, Chelioprion, Chromis, Chrysiptera, Dascyllus, Pristotis, Dischistodus, Hemiglyphidodon, Neoglyphidodon, Neopomacentrus, Plectroglyphidodon, Pomacentrus, Stegastes) and at least 39 species inhabit the waters of Peninsular Malaysia and Singapore. They are important ecologically because many species are extremely abundant in reefs, and also economically, as several are collected in large numbers for the lucrative aquarium trade. This demand has led to some fishermen using destructive methods in obtaining the fishes, to the point that original standing populations may not be recoverable. This threat poses a need for conservation of the reefs. The present study based primarily on fishes collected from the waters of Singapore and specimens from the Zoological Reference Collection at the National University of Singapore, will serve the dual purpose of establishing a current species list for Malaysia and Singapore, and to update and clarify the local taxonomy of the group. An annotated list (with localities) is provided of the known or reported species to aid studies on reefs.     

A new cluster model for the FeMo-cofactor of nitrogenase.

A new structural model for the FeMo-cofactor of nitrogenase, consisting of two Fe₄S₄ clusters bridged by an S₂Mo₂ unit, is proposed. Available chemical, spectroscopic, and EXAFS data are shown to be consistent with the proposed structure. In particular, EXAFS data are in agreement with m(Mo-Fe):n(Mo-S) of either 2:4 or 3:4; comparison with known Mo-Fe-S and Fe-S systems leads us to favor the former. Based on the proposed structural model, a possible mechanism of reduction of N₂ is suggested.