Three lines of evidence suggest that tail formation in Xenopus is a direct continuation of events initiated during gastrulation. First, the expression of two gene markers, Xbra and Xnot2, can be followed from the blastopore lip into distinct cell populations of the developing tailbud. Second, the tip of the tail retains Spemann's tail organizer activity until late stages of development. Third, ...

This review explores the historical and current state of our knowledge about urodele limb regeneration. Topics discussed are (1) blastema formation by the proteolytic histolysis of limb tissues to release resident stem cells and mononucleate cells that undergo dedifferentiation, cell cycle entry and accumulation under the apical epidermal cap. (2) The origin, phenotypic memory, and positional m...

Blastema formation, which is the first step of regeneration in adult Metazoa, is generally considered to be merely an accumulation of undifferentiated cells provided by mitotic activity, which occurs near the wound following amputation. Afterwards, these undifferentiated cells are thought to differentiate rapidly, thus affecting the organization of the regenerate. Some authors have postulated t...

The mechanisms by which cells obtain instructions to precisely re-create the missing parts of an organ remain an unresolved question in regenerative biology. Urodele limb regeneration is a powerful model in which to study these mechanisms. Following limb amputation, blastema cells interpret the proximal-most positional identity in the stump to reproduce missing parts faithfully. Classical exper...

An open question remains in cancer stem cell (CSC) biology whether CSCs are by definition at the top of the differentiation hierarchy of the tumor. Wilms' tumor (WT), composed of blastema and differentiated renal elements resembling the nephrogenic zone of the developing kidney, is a valuable model for studying this question because early kidney differentiation is well characterized. WT neural ...

BACKGROUND Nuclear unrest is a term applied to Wilms' tumors (WT) that show nuclear abnormalities close to anaplasia but without abnormal mitoses. p53 is claimed to be associated with anaplasia and poor prognosis. This study was undertaken to evaluate the clinical significance of nuclear unrest and p53 immunostaining in Wilms' tumor. MATERIAL AND METHODS This is a retrospective study of 63 pa...

Two closely related fibroblast growth factor receptors, FGFR1 and FGFR2, have been cloned from a newt (Notophthalmus viridescens) limb blastema cDNA library. Sequence analysis revealed that we have isolated both the bek and KGFR variants of FGFR2. These two variants differ only in the second half of the last of their three Ig-like domains. The expression patterns of FGFR1 and FGFR2 during limb ...

An assay that detects position-related differences in affinity of axolotl regeneration blastema cells in vivo was used to test whether retinoic acid, which proximalizes regenerate pattern, simultaneously proximalizes blastema cell affinity. The assay involved autografting or homografting late bud forelimb blastomas derived from the wrist, elbow or midupper arm levels to the dorsal surface of th...

Regeneration is an ability that has been observed extensively throughout metazoan phylogeny. Amongst vertebrates, the urodele amphibians stand out for their exceptional capacity to regenerate body parts such as the limb. During this process, only the missing portion of the limb is precisely replaced--amputation in the upper arm results in regeneration of the entire limb, while amputation at the...

Previous studies of zebrafish fin regeneration led to the notion that the regeneration blastema is a homogeneous population of proliferating cells. Here, we show that the blastema consists of two components with markedly distinct proliferation properties. During early blastema formation, proliferating cells are evenly distributed. At the onset of regenerative outgrowth, however, blastemal cells...