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ADAM metalloproteinase disintegrins have emerged as the major proteinase family that mediates ectodomain shedding, the proteolytic release of extracellular domains from their membrane-bound precursors. Recent gene-manipulation studies have established the role of ADAM-mediated shedding in mammalian physiology and, in addition, raised the issue of functional redundancy among ADAM sheddases. ADAM sheddases activate, for example, growth factors and cytokines, thus regulating signalling pathways that are important in development and pathological processes such as cancer. The recent studies have also begun to elucidate the substrate specificity and the mechanisms that control ADAM-mediated shedding events that regulate, for example, growth-factor and Notch signalling, and the processing of the amyloid precursor protein.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tibs.2005.05.006 Byline: Ari-Pekka J. Huovila (a), Anthony J. Turner (b), Markku Pelto-Huikko (c), Iivari Karkkainen (a), Rebekka M. Ortiz (a) Abstract: ADAM metalloproteinase disintegrins have emerged as the major proteinase family that mediates ectodomain shedding, the proteolytic release of extracellular domains from their membrane-bound precursors. Recent gene-manipulation studies have established the role of ADAM-mediated shedding in mammalian physiology and, in addition, raised the issue of functional redundancy among ADAM sheddases. ADAM sheddases activate, for example, growth factors and cytokines, thus regulating signalling pathways that are important in development and pathological processes such as cancer. The recent studies have also begun to elucidate the substrate specificity and the mechanisms that control ADAM-mediated shedding events that regulate, for example, growth-factor and Notch signalling, and the processing of the amyloid precursor protein. Author Affiliation: (a) Institute of Medical Technology, University of Tampere and Tampere University Hospital, Biokatu 6, FIN-33520 Tampere, Finland (b) Proteolysis Research Group, School of Biochemistry and Microbiology, University of Leeds, Leeds LS2 9JT, UK (c) Departments of Developmental Biology and Pathology, University of Tampere Medical School and Tampere University Hospital, 33014 University of Tampere, Finland

A forkhead gene, FoxE3, has been shown to be necessary for closure of the lens vesicle and lens epithelial proliferation in eye development. The cloning of this gene, expressed in the lens epithelium, has been carried out. It is mutated in a classic mouse model with ensuing defective lens development. In the mouse mutant dysgenetic lens (dyl) the lens vesicle does not separate from the ectoderm and fusion between lens and cornea results. With no proliferating anterior lens epithelium absence of secondary lens fibers and a dysplastic cataractic lens results.

The forkhead transcription factor FREAC-1 is a potent transcriptional activator. We have localized a transcriptional activation domain in the C-terminus of FREAC-1 and another one to a stretch of approximately 60 amino acids in the central part of the protein. While the C-terminal activation domain activates in all cell lines tested, the activation domain in the central part of the protein is functional only in cell lines derived from lung. This cell-type-specific activity is retained when the activation domain is fused to the heterologous DNA binding domain of Ga14. The human FREAC-1 gene was found to consist of two exons separated by an intron of 1.2 kb. Exon 1 encodes the forkhead DNA binding domain and the cell-type-specific activation domain. Exon 2 encodes the general activation domain. The distribution of FREAC-1 expression during embryogenesis was investigated by in situ hybridization. FREAC-1 mRNA was found in mesenchyme in immediate proximity to endodermal epithelia throughout the digestive, urinary, and respiratory tracts. Mesenchyme surrounding the notochord and adjacent to the ectodermal epithelia of the oral cavity and developing teeth also expresses FREAC-1. The pattern of FREAC-1 expression, with highest levels in the mesenchyme next to the epithelium and gradually diminishing as the distance from the epithelium increases, suggests that FREAC-1 expression is a response to epithelial paracrine signaling and that FREAC-1 may play a role in epitheliomesenchymal interactions.

We have cloned a novel member of the nuclear receptor superfamily. The cDNA of clone 29 was isolated from a rat prostate cDNA library and it encodes a protein of 485 amino acid residues with a calculated molecular weight of 54.2 kDa. Clone 29 protein is unique in that it is highly homologous to the rat estrogen receptor (ER) protein, particularly in the DNA-binding domain (95%) and in the C-terminal ligand-binding domain (55%). Expression of clone 29 in rat tissues was investigated by in situ hybridization and prominent expression was found in prostate and ovary. In the prostate clone 29 is expressed in the epithelial cells of the secretory alveoli, whereas in the ovary the granulosa cells in primary, secondary, and mature follicles showed expression of clone 29. Saturation ligand-binding analysis of in vitro synthesized clone 29 protein revealed a single binding component for 17[Beta]-estradiol (E2) with high affinity ([K.sub.d] = 0.6 nM). In ligand-competition experiments the binding affinity decreased in the order E2 > diethylstilbestrol > estriol > estrone > 5[Alpha]-androstane-3[Beta], 17[Beta]-diol >> testosterone = progesterone = corticosterone = 5[Alpha]-androstane-3[Alpha], 17[Beta]-diol. In cotransfection experiments of Chinese hamster ovary cells with a clone 29 expression vector and an estrogen-regulated reporter gene, maximal stimulation (about 3-fold) of reporter gene activity was found during incubation with 10 nM of E2. Neither progesterone, testosterone, dexamethasone, thyroid hormone, all-trans-retinoic acid, nor 5[Alpha]-androstane-3[Alpha], 17[Beta]-diol could stimulate reporter gene activity, whereas estrone and 5[Alpha]-androstane-3[Beta], 17[Beta]-diol did. We conclude that clone 29 cDNA encodes a novel rat ER, which we suggest be named rat ER[Beta] to distinguish it from the previously cloned ER (ER[Alpha]) from rat uterus.

The role of beta-nerve growth factor (b-NGF) in spermatogenesis was investigated by studying the stage specific expression of NGF and its low-affinity receptor (LAR) during the cycle of the rat seminiferous epithelium. The results showed that NGF mRNA and protein are present at all cycle stages, whereas LAR mRNA appeared only at stages VII(sub cd) and VIII. Furthermore, LAR protein was found in the plasma membrane of Sertoli cells from stages VII(sub cd) to XI. It seems that NGF promotes DNA synthesis at the onset of meiosis through a stage-specific NGF receptor in Sertoli cells.