Structure, expression and function of a schwannoma-derived growth factor

During the development of the nervous system, cells require growth factors that regulate their division and survival. To identify new growth factors, serum-free growth-conditioned media from many clonal cell lines were screened for the presence of mitogens for central nervous system glial cells. A cell line secreting a potent glial mitogen was established from a tumour (or 'schwannoma') derived from the sheath of the sciatic nerve. The cells of the tumour, named JS1 cells, were adapted to clonal culture and identified as Schwann cells. Schwann cells secrete an autocrine mitogen and human schwannoma extracts have mitogenic activity on glial cells. Until now, neither mitogen has been purified. Here we report the purification and characterization of a mitogenic molecule, designated schwannoma-derived growth factor (SDGF), from the growth-conditioned medium of the JS1 Schwann cell line. SDGF belongs to the epidermal growth factor family, and is an autocrine growth factor as well as a mitogen for astrocytes, Schwann cells and fibroblasts.     

Regulation of cell cycle progression and gene expression by H2A deubiquitination

Post-translational histone modifications have important regulatory roles in chromatin structure and function. One example of such modifications is histone ubiquitination, which occurs predominately on histone H2A and H2B. Although the recent identification of the ubiquitin ligase for histone H2A has revealed important roles for H2A ubiquitination in Hox gene silencing as well as in X-chromosome inactivation, the enzyme(s) involved in H2A deubiquitination and the function of H2A deubiquitination are not known. Here we report the identification and functional characterization of the major deubiquitinase for histone H2A, Ubp-M (also called USP16). Ubp-M prefers nucleosomal substrates in vitro, and specifically deubiquitinates histone H2A but not H2B in vitro and in vivo. Notably, knockdown of Ubp-M in HeLa cells results in slow cell growth rates owing to defects in the mitotic phase of the cell cycle. Further studies reveal that H2A deubiquitination by Ubp-M is a prerequisite for subsequent phosphorylation of Ser 10 of H3 and chromosome segregation when cells enter mitosis. Furthermore, we demonstrate that Ubp-M regulates Hox gene expression through H2A deubiquitination and that blocking the function of Ubp-M results in defective posterior development in Xenopus laevis. This study identifies the major deubiquitinase for histone H2A and demonstrates that H2A deubiquitination is critically involved in cell cycle progression and gene expression.     

Induction of a novel epidermal growth factor-secreting cell lineage by mucosal ulceration in human gastrointestinal stem cells

Epidermal growth factor, and its human homologue urogastrone (EGF/URO), are secreted by the gut-associated salivary and Brunner's glands. Recombinant EGF/URO is a powerful stimulator of cell proliferation and differentiation in the rodent and neonatal human intestine. But EGF/URO is not absorbed from the adult gut and has no action when given through the gut lumen; thus the role of secreted EGF/URO is unknown. We now report that ulceration of the epithelium anywhere in the human gastrointestinal tract induces the development of a novel cell lineage from gastrointestinal stem cells. This lineage initially appears as a bud from the base of intestinal crypts, adjacent to the ulcer, and grows locally as a tubule, ramifying to form a new small gland, and ultimately emerges onto the mucosal surface. The lineage produces neutral mucin, shows a unique lectin-binding profile and immunophenotype, is nonproliferative, and contains and secretes abundant immunoreactive EGF/URO. We propose that all gastrointestinal stem cells can produce this cell lineage after mucosal ulceration, secreting EGF/URO to stimulate cell proliferation, regeneration and ulcer healing. This cell lineage is very commonly associated with gastrointestinal mucosal ulceration, and we conclude that a principal in vivo role for EGF/URO is to stimulate ulcer healing throughout the gut through induction of this cell lineage in the adjacent mucosa.     

Sonic hedgehog调控T细胞分化和功能的研究

T细胞是体内重要的免疫细胞,T细胞介导的细胞免疫应答参与了肿瘤、自身免疫性疾病等疾病的病理生理过程.研究T细胞分化和功能调控机制将有助于阐明相关疾病的发病机制,并为疾病防治提供思路.近来有国外研究显示,早期胚胎发育过程中的关键成形素(mophorgen)--Sonic hedgehog(SHH)不仅调控T细胞发育的各个...     

Regulation of cell movement is mediated by stretch-activated calcium channels.

Intracellular calcium regulates many of the molecular processes that are essential for cell movement. It is required for the production of actomyosin-based contractile forces, the regulation of the structure and dynamics of the actin cytoskeletons, and the formation and disassembly of cell-substratum adhesions. Calcium also serves as a second messenger in many biochemical signal-transduction pathways. However, despite the pivotal role of calcium in motile processes, it is not clear how calcium regulates overall cell movement. Here we show that transient increases in intracellular calcium, [Ca2+]i, during the locomotion of fish epithelial keratocytes, occur more frequently in cells that become temporarily 'stuck' to the substratum or when subjected to mechanical stretching. We find that calcium transients arise from the activation of stretch-activated calcium channels, which triggers an influx of extracellular calcium. In addition, the subsequent increase in [Ca2+]i is involved in detachment of the rear cell margin. Thus, we have defined a mechanism by which cells can detect and transduce mechanical forces into biochemical signals that can modulate locomotion.     

Embryonic expression of a haematopoietic growth factor encoded by the Sl locus and the ligand for c-kit.

Mice carrying mutations at the W (Dominant white spotting) and Sl (Steel) loci develop abnormalities in three independent systems: neural crest-derived melanocytes, primordial germ cells and haematopoietic stem cells. Consequently, homozygotes of viable mutant alleles have white coats and are sterile and severely anaemic. Tissue recombination studies predict that the W gene is expressed cell autonomously, whereas the product of the Sl locus affects the microenvironment in which the stem cells migrate, proliferate and differentiate. The W locus encodes the protoncogene c-kit, a member of the tyrosine kinase receptor family. The haematopoietic growth factor SCF (stem cell factor) has been identified as the product of the Sl locus and a ligand for c-kit. Here, we report that SCF is expressed during embryogenesis in cells associated with both the migratory pathways and homing sites of melanoblasts, germ cells and haematopoietic stem cells. Both SCF and c-kit are also expressed in a variety of other tissues, including the brain and spinal cord, suggesting that the receptor-ligand system has additional roles in embryogenesis.     

An essential role for a phospholipid transfer protein in yeast Golgi function

Progression of proteins through the secretory pathway of eukaryotic cells involves a continuous rearrangement of macromolecular structures made up of proteins and phospholipids. The protein SEC14p is essential for transport of proteins from the yeast Golgi complex. Independent characterization of the SEC14 gene and the PIT1 gene, which encodes a phosphatidylinositol/phosphatidylcholine transfer protein in yeast, indicated that these two genes are identical. Phospholipid transfer proteins are a class of cytosolic proteins that are ubiquitous among eukaryotic cells and are distinguished by their ability to catalyse the exchange of phospholipids between membranes in vitro. We show here that the SEC14 and PIT1 genes are indeed identical and that the growth phenotype of a sec14-1ts mutant extends to the inability of its transfer protein to effect phospholipid transfer in vitro. These results therefore establish for the first time an in vivo function for a phospholipid transfer protein, namely a role in the compartment-specific stimulation of protein secretion.     

Regulation of ovarian function by the matrix metalloproteinase system

In most organs of mammals, cyclic remodelling of tissues after morphogenesis is minimal; however, repro-ductive tissues of female animals including endometrium, mammary gland, ovarian follicle and corpus luteum un-dergo growth, maturation and involution at various stages in the reproductive cycle or lifespan of the animal. Recon-struction of the extracellular matrix (ECM) is required for the dynamic tissue reorganization characteristic of these tissues. The ECM consists of proteinaceous and nonpro-teinaceous molecules that provide the tissue-specific, ex-tracellular architecture to which cells attach. Furthermore, interaction of cellular receptors with proteins of the ECM can regulate cellular structure, second messenger genera-tion and gene expression. Maintenance of ECM homeo-stasis depends largely on coordinated action of matrix metalloproteinases (MMPs) and tissue inhibitors of met-alloproteinases (TIMPs)-- an important proteinase sys-tem responsible for degradating and remodelling of ECM[1]. MMPs/TIMPs have been recognized as the cru-cial role players in regulating follicular and luteal function for their extensive involvements in the cyclic changes of dynamic ovarian tissues. In recent years, literature that MMP system has important roles in ovary is accumulating. The focus of this review is on the effects of MMPs and their inhibitors, TIMPs on follicular growth, atresia, ovu-lation, luteal development, and luteolysis. Emphasis has been given to the recent progress in the new field when-ever possible.     

Regulation of axon growth in vivo by activity-based competition

The formation of functional neural networks requires precise regulation of the growth and branching of the terminal arbors of axons, processes known to be influenced by early network electrical activity. Here we show that a rule of activity-based competition between neighbouring axons appears to govern the growth and branching of retinal ganglion cell (RGC) axon arbors in the developing optic tectum of zebrafish. Mosaic expression of an exogenous potassium channel or a dominant-negative SNARE protein was used to suppress electrical or neurosecretory activity in subsets of RGC axons. Imaging in vivo showed that these forms of activity suppression strongly inhibit both net growth and the formation of new branches by individually transfected RGC axon arbors. The inhibition is relieved when the activity of nearby 'competing' RGC axons is also suppressed. These results therefore identify a new form of activity-based competition rule that might be a key regulator of axon growth and branch initiation.     

DNA sequence for a low-level promoter of the lac repressor gene and an 'up' promoter mutation.

The promoter for a weakly expressed constitutive gene, the lactose repressor gene (lacI), has been sequenced, along with an 'up' promoter mutation Iq. The 10-fold enhancement in I expression found in Iq is the result of a single base change at position -35. To facilitate the sequencing, the lacI gene was cloned in a small plasmid.