The effect of catecholamines and adenosine on the induction of morphological alterations and depigmentation of newt iris epithelial cells in vitro

High-throughput, high-content screening for novel pigmentation regulators using a keratinocyte/melanocyte co-culture system

Skin pigmentation is a complex process including melanogenesis within melanocytes and melanin transfer to the keratinocytes. To develop a comprehensive screening method for novel pigmentation regulators, we used immortalized melanocytes and keratinocytes in co-culture to screen large numbers of compounds. High-throughput screening plates were subjected to digital automated microscopy to quantify the pigmentation via brightfield microscopy. Compounds with pigment suppression were secondarily tested for their effects on expression of microphthalmia transcription factor (MITF) and several pigment regulatory genes, and further validated in terms of non-toxicity to keratinocytes/melanocytes and dose-dependent activity. The results demonstrate a high-throughput, high-content screening approach, which is applicable to the analysis of large chemical libraries using a co-culture system. We identified candidate pigmentation inhibitors from 4000 screened compounds including zoxazolamine, 3-methoxycatechol and alpha-mangostin, which were also shown to modulate expression of MITF and several key pigmentation factors and are worthy of further evaluation for potential translation to clinical use.

Signalling from adenosine receptors to mitogen-activated protein kinases

The purine nucleoside adenosine acts via four distinct adenosine receptor subtypes: the adenosine A(1), A(2A), A(2B), and A(3) receptor. They are all G protein-coupled receptors (GPCR) coupling to classical second messenger pathways such as modulation of cAMP production or the phospholipase C (PLC) pathway. In addition, they couple to mitogen-activated protein kinases (MAPK), which could give them a role in cell growth, survival, death and differentiation. Although each of the adenosine receptors can activate one or more of the MAPKs, the mechanisms appear to differ substantially, both between receptor subtypes in the same cell type and between the same receptor in different cell types.

Macrophage mobilization and morphology during lens regeneration from the iris epithelium in newts: studies with correlated scanning and transmission electron microscopy

The lens was removed from both eyes of adult newts (Notophthalmus viridescens), and the eyes were fixed in Karnovsky's fixative every 2 days 0-20 days after operation. Anterior half-eyes were prepared by standard procedures for scanning electron microscopy of the surface. Before fixation, the posterior iris surface was cleaned of adhering vitreous mechanically with forceps or by treatment with bovine testicular hyaluronidase or with hyaluronidase and collagenase. Some specimens were cryofractured in buffer or ethanol transverse to the mid-dorsal iris, and the fractured surface viewed with scanning electron microscopy (SEM). Cells with various combinations of ridges, blebs, filopodia, and lamellipodia were observed adhering to the posterior surface of the iris by 6 days after lentectomy. These cells, which exhibited the surface characteristics of macrophages, became more numerous in specimens fixed after longer intervals. Invasion of the iris epithelium was observed in a cryofractured specimen. After observations with SEM, selected specimens were embedded in plastic and sectioned for study with transmission electron microscopy (TEM). The cells on the iris surface had the cytological characteristics of macrophages, and other macrophages were located within the iris epithelium. In specimens fixed 16 or more days after lentectomy, a bulging lens vesicle was regenerating from the dorsal pupillary margin of the iris. Macrophages were absent or few on the surface of this developing lens but remained scattered over the adjoining iris. Roles that might be played by these macrophages during the transdifferentiation of iris epithelium into lens are discussed.

Cell type expression mediated by cell cycle events, and signaled by mitogens and growth inhibitors

It is initially pointed out that the majority of factors that induce cell type expression in mature precursor cells are either mitogens or growth inhibitors. On the basis of available data, a theoretical model of regulation of cell type expression for each group of factors is proposed. In model A the mitogen affects the expression of cell type through the positive control of cell cycle progression, while in model B the growth inhibitor induces the negative control of cell cycle progression, which in its turn causes the cell type expression. In connection with those two models, various systems of cell type expression are classified into three groups. In model A systems, the cell lineage has an option of autotypic and allotypic cell types. The former is expressed in the absence of added mitogen, and the latter is expressed in its presence. In model B systems the cell lineage-specific cell type is expressed by the negative cell cycle control induced by the growth inhibitor. In model A-B systems both mitogen and inhibitor are needed in tandem for the expression of a cell type. The second major point made is that the expression of cell type follows the negative control of cell cycle progression even in model A systems. However, in this system the control occurs spontaneously. This suggests that the negative control is essential for cell type expression in all systems, and directly precedes the expression. In contrast, the positive control induced by exogenous mitogen is not required in the expression in model B systems or in that of autotypic cell types in model A systems. The third point is that on the basis of the hypothesis of replication-transcription coupling, proposed by Sauer and colleagues, it is speculated that the pattern of early-replicating genes may be functioning as the potential gene transcription pattern for cell type expression in precursor cells. If this pattern is perpetuated through cell generations, the original cell type specificity of the precursor cell lineage should be maintained. If this pattern is modified by the positive control of cell cycle progression in model A systems, the potential transcriptional pattern for the allotypic pathway may emerge. Furthermore, it is proposed that the realization of the potential pattern may depend on a signal, informing the completion of the negative control of cell cycle progression. Thus in all cell lineages, when the negative cell cycle control is completed, chromatin receives this signal, and the potential transcription pattern is converted into cell type differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)