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How did cells of early metazoan organisms first organize themselves to form a body axis? The canonical Wnt pathway has been shown to be sufficient for induction of axis in Cnidaria, a sister group to Bilateria, and is important in bilaterian axis formation. Here, we provide experimental evidence that in cnidarian Hydra the Hippo pathway regulates the formation of a new axis during budding upstream of the Wnt pathway. The transcriptional target of the Hippo pathway, the transcriptional coactivator YAP, inhibits the initiation of budding in Hydra and is regulated by Hydra LATS. In addition, we show functions of the Hippo pathway in regulation of actin organization and cell proliferation in Hydra. We hypothesize that the Hippo pathway served as a link between continuous cell division, cell density, and axis formation early in metazoan evolution.

Fat, Fat-like, and Dachsous family cadherins are giant proteins that regulate planar cell polarity (PCP) and cell adhesion in bilaterians. Their evolutionary origin can be traced back to prebilaterian species, but their ancestral function(s) are unknown. We identified Fat-like and Dachsous cadherins in Hydra, a member of phylum Cnidaria a sister group of bilaterian. We found Hydra does not possess a true Fat homolog, but has homologs of Fat-like (HyFatl) and Dachsous (HyDs) that localize at the apical membrane of ectodermal epithelial cells and are planar polarized perpendicular to the oral-aboral axis of the animal. Using a knockdown approach we found that HyFatl is involved in local cell alignment and cell-cell adhesion, and that reduction of HyFatl leads to defects in tissue organization in the body column. Overexpression and knockdown experiments indicate that the intracellular domain (ICD) of HyFatl affects actin organization through proline-rich repeats. Thus, planar polarization of Fat-like and Dachsous cadherins has ancient, prebilaterian origins, and Fat-like cadherins have ancient roles in cell adhesion, spindle orientation, and tissue organization.

The atypical cadherin FAT4 has established roles in the regulation of planar cell polarity and Hippo pathway signaling that are cell context dependent. The recent identification of FAT4 mutations in Hennekam syndrome, features of which include lymphedema, lymphangiectasia, and mental retardation, uncovered an important role for FAT4 in the lymphatic vasculature. Hennekam syndrome is also caused by mutations in collagen and calcium binding EGF domains 1 (CCBE1) and ADAM metallopeptidase with thrombospondin type 1 motif 3 (ADAMTS3), encoding a matrix protein and protease, respectively, that regulate activity of the key prolymphangiogenic VEGF-C/VEGFR3 signaling axis by facilitating the proteolytic cleavage and activation of VEGF-C. The fact that FAT4, CCBE1, and ADAMTS3 mutations underlie Hennekam syndrome suggested that all 3 genes might function in a common pathway. We identified FAT4 as a target gene of GATA-binding protein 2 (GATA2), a key transcriptional regulator of lymphatic vascular development and, in particular, lymphatic vessel valve development. Here, we demonstrate that FAT4 functions in a lymphatic endothelial cell-autonomous manner to control cell polarity in response to flow and is required for lymphatic vessel morphogenesis throughout development. Our data reveal a crucial role for FAT4 in lymphangiogenesis and shed light on the mechanistic basis by which FAT4 mutations underlie a human lymphedema syndrome., Introduction Hennekam syndrome (OMIM #235510 and #616006) is an autosomal-recessive disorder characterized by congenital lymphedema and lymphangiectasia, unusual facial morphology, attributed at least in part to intrauterine facial lymphedema, and [...]

Doctors in specialist training posts in the Mersey Deanery are expected to reflect on their clinical practice and to document their learning experiences in an e-portfolio. This study aims specifically to explore how they have engaged in reflection on their practice and how they utilise their learning portfolio to document evidence of this. A modified Delphi technique was used to develop a grading system to identify the level of reflection recorded by participants in the e-portfolio. Transcripts of the reflective accounts were then analysed using a qualitative approach which involved coding and categorising the data. This study demonstrated a wide variation in both the quantity and quality of reflection. Of particular note in the qualitative data analysis were themes relating to clinical knowledge and skills, learning in practice, communication, feelings, types of learning experience reflected on and wider aspects of medical practice. Findings indicate there is variation is the extent to which doctors both engage in and document evidence of reflection. Further research is needed to explore factors that enable or inhibit the use of the e-portfolio for reflection and whether recorded reflection is a true picture of the cognitive process involved. (Contains 2 tables.)

Determining how growth and differentiation are coordinated is key to understanding normal development, as well as disease states such as cancer, where that control is lost. We have previously shown that growth and neuronal differentiation are coordinated by the insulin receptor/target of rapamycin (TOR) kinase (InR/TOR) pathway. Here we show that the control of growth and differentiation diverge downstream of TOR. TOR regulates growth by controlling the activity of $6 kinase (S6K) and eIF4E. Loss of s6k delays differentiation, and is epistatic to the loss of tsc2, indicating that S6K acts downstream or in parallel to TOR in differentiation as in growth. However, loss of eIF4E inhibits growth but does not affect the timing of differentiation. We also show, for the first time in Drosophila, that there is crosstalk between the InR/TOR pathway and epidermal growth factor receptor (EGFR) signaling. InR/TOR signaling regulates the expression of several EGFR pathway components including pointedP2 (pntP2). In addition, reduction of EGFR signaling levels phenocopies inhibition of the InR/TOR pathway in the regulation of differentiation. Together these data suggest that InR/TOR signaling regulates the timing of differentiation through modulation of EGFR target genes in developing photoreceptors.

Iroquois transcription factors regulate diverse aspects of developmental patterning in all metazoans. Despite their widespread importance, the direct targets of the Iroquois are poorly understood. Here, we use in vitro site selection to define the DNA-binding preference of the Drosophila Iroquois Mirror. We use electrophoretic mobility shift assays to determine the critical nucleotides for Mirror binding and to show that this site is recognized by other Drosophila Iroquois transcription factors. This site also is recognized by vertebrate Iroquois transcription factors. Transgenic analysis demonstrates that Drosophila Iroquois proteins recognize this site in vivo to mediate transcriptional repression. We further show that Iroquois transcription factors form homodimers and heterodimers, suggesting that combinatorial binding may contribute to gene regulation by this family. development | Drosophila | Notch | planar polarity | fringe

Author(s): Dali Ma [1]; Chung-hui Yang [2]; Helen McNeill [3]; Michael A. Simon [2]; Jeffrey D. Axelrod (corresponding author) [1] The polarity of Drosophila wing hairs displays remarkable fidelity. Each [...]