Search PubMed⌕ Search

Biomedical subjects

M Smalley

Publications and source records attributed to M Smalley.

6 recordsLinked to original sources
PubMed2000

Wnt/Shh interactions regulate ectodermal boundary formation during mammalian tooth development.

Interactions between the Wnt (wingless) and hedgehog signaling pathways were first described as playing a role in establishing boundaries between ectodermal cells in Drosophila segmentation. During the initiation of mammalian tooth development, boundaries that distinguish oral from dental ectoderm must be formed to correctly position the sites of tooth formation. We describe a reciprocal relationship between the expression of Wnt-7b in presumptive oral ectoderm and Shh in presumptive dental ectoderm in mouse embryos that mark boundaries between these cells with different developmental fates. By using a murine retrovirus to ectopically express Wnt-7b in presumptive dental ectoderm in mandibular arch explants, we show that Shh expression in the ectoderm and Ptc expression in the underlying ectomesenchyme are down-regulated, and tooth development is subsequently arrested. This suggests that Wnt-7b acts to repress Shh expression in oral ectoderm, thus maintaining the boundaries between oral and dental ectodermal cells. Implantation of beads soaked in Shh protein into Wnt-7b-infected explants resulted in complete rescue of tooth development, confirming that the repressive action of Wnt-7b specifically affects Shh signaling.

Animals↗
PubMed2000

Sequence variants of the axin gene in breast, colon, and other cancers: an analysis of mutations that interfere with GSK3 binding.

Axin is a recently discovered component of a multiprotein complex containing APC, beta-catenin, GSK3, and PP2A, which functions in the degradation of the beta-catenin protein. As part of WNT signal transduction, the function of the Axin complex is inhibited, leading to the accumulation of beta-catenin. The inappropriate stabilization of beta-catenin has been implicated in a range of human tumors. Two oncogenic mechanisms leading to beta-catenin stabilization are the loss of the APC tumor suppressor protein and the mutational activation of beta-catenin, such that the Axin/APC complex can no longer regulate it. Studies in Drosophila and mammalian tissue culture showed loss of Axin function interfered with beta-catenin turnover and activated beta-catenin/TCF-dependent transcription. Based on these observations, Axin was screened for mutations in a range of human tumor cell lines and primary breast tumor samples. We identified two sequence variants causing amino acid substitutions in four colon cancer cell lines, a Ser-to-Leu at residue 215 in LS513 and a Leu-to-Met at residue 396 in HCT-8, HCT-15, and DLD-1. The Axin L396M mutation was selected for further study since it lay within a region that was shown to interact with glycogen synthase kinase-3. Biochemical and functional studies showed that the L396M change interfered with Axin's ability to bind GSK3. Interestingly, this mutation and a neighboring L392M change differentially altered Axin's ability to interfere with two upstream activators of TCF-dependent transcription, Frat1 and Disheveled.

Amino Acid Sequence↗
PubMed1999

Behavior of a cell line derived from normal human hepatocytes on non-physiological and physiological-type substrates: evidence for enhancement of secretion of liver-specific proteins by a three-dimensional growth pattern.

The behavior of a recently described cell line, HH25, derived from normal human hepatocytes, has been investigated on several different substrates--tissue-culture plastic, glass, a thin layer of rat-tail collagen I, and thin layers or thick gels of extracellular matrix derived from the Engelbreth-Holm-Swarm murine sarcoma (EHS matrix). Cellular morphology, proliferation, and secretion of three hepatocyte-specific proteins (albumin, alpha1 acid glycoprotein, and alpha1 antitrypsin) have been examined. There were no differences in morphology, proliferation, or differentiated function in the cells on either plastic, glass, collagen, I, or a thin layer of EHS matrix, but on a thick EHS matrix gel the cells altered their morphology (forming three-dimensional colonies with canalicular-like structures) and their production of albumin and alpha1 acid glycoprotein was enhanced. This suggests that the enhanced differentiated function is associated with the morphological change (occurring only on the thick EHS gel) rather than with receptor-mediated cell-matrix interactions (which can also occur on the thin layer of EHS matrix). This cell line is therefore a good in vitro cellular model for the investigation of the roles of morphological changes and of cell-cell and cell-matrix interactions in the control of human hepatocyte behavior without the need for an extensive source of primary tissue.

Albumins↗