We examined emergent leadership in small online collaborative learning groups of pre-service math and science teachers. Groups worked online to design interdisciplinary instructional units. We employed a distributed leadership framework (Spillane, 2007) and adapted a coding system previously developed by Li, et al. (2007) to determine that group leadership was highly distributed among participa...

The different papers in this special issue all addressed learning with complex tasks. All of these papers reached only partially the expected results. This discussion on possible factors that may explain these unexpected results. A first issue that is questioned is the functionality of the tools in the studies. Secondly, the learners lack of compliance is addressed. It may have been that the le...

The discovery of the organizer by Spemann and Mangold in 1924 raised two kinds of questions: those about the means of patterning the chordate body axis and those about the mechanisms of cell determination by induction. Some researchers, stressing the second, have suggested over the years that the organizer is poorly named and doesn't really organize because inducers act permissively, because th...

Maternal Wnt11 is both necessary and sufficient for the formation of Spemann organizer in Xenopus embryo. Xnr3 and Siamois have been identified as the direct target genes of maternal Wnt11/β-catenin during organizer induction. The depletion of maternal XTcf3 resulted in the ectopic expression of Xnr3 and Siamois, suggesting the activity of β-catenin/XTcf3 is strictly regulated in the early Xeno...

The vertebrate organizer has been of intense interest since its discovery in amphibia by Spemann and Mangold in the early 1920s (Ref. 1). The organizer was operationally defined as a piece of tissue that can induce a duplicated dorsal body axis and head when transplanted into the ventral side of a host embryo. The original Spemann and Mangold organizer experiment provided the first convincing d...

nucleolar organizer regions (nor) are defined as nucleolar components containing a set of argyrophilic proteins which are selectively stained by colloidal silver nitrate staining. although studies have shown that the number of nor dots or particles is directly related to the rapidity of cell proliferation in cancer cells, prognostic or diagnostic value of nor remains controversial. the aim of t...

Systematic genetic screens in zebrafish have led to the discovery of mutations that affect organizer function and development. The molecular isolation and phenotypic analysis of the affected genes have revealed that TGF-beta signals of the Nodal family play a key role in organizer formation. The activity of the Nodal signals Cyclops and Squint is regulated extracellularly by the EGF-CFC cofacto...

in 1909, several years before the famous `organizer’ experiments of spemann and mangold, ethel browne demonstrated induction of a secondary axis in hydra by grafting a hypostome. based on this and subsequent work, in the late sixties, lewis wolpert proposed the theory of morphogen gradients and positional information. we have studied secondary axis induction by hypostome and foot tissue using t...

The organizer is a unique region in the gastrulating embryo that induces and patterns the body axis. It arises before gastrulation under the influence of the Nieuwkoop center. We show that during gastrulation, cell movements bring cells into and out of the chick organizer, Hensen's node. During these movements, cells acquire and lose organizer properties according to their position. A "node ind...