Regenerative capability of upper and lower jaws in the newt.
The regenerating amphibian jaw represents an important model for studying pattern formation and the mechanisms underlying regeneration of facial structures. We have studied regeneration of upper and lower jaws in the urodele amphibian, Notophthalmus viridescens, using whole mount preparations stained for bone and cartilage, scanning electron microscopy and immunocytochemistry to further characterize these regenerating systems. In addition, we have investigated whether lower jaws of adults and larvae display similar regenerative ability. Although in adult animals the original shape of both the lower and upper jaws is rather faithfully reproduced following amputation, and the teeth and oral mucosa with its specialized sensory organs fully regenerate, significant differences in the regenerative ability of the various skeletal elements are observed. In fact, only tooth-bearing skeletal elements ossify, while the other elements of the regenerated skeleton remain cartilaginous for as long as 5 months after amputation. In contrast, a regenerated lower jaw in the larva is indistinguishable from an unamputated one at the same stage of development. Interestingly, regenerating adult jaws form directly bicuspid teeth, which are the type of teeth normally found in the adult, rather than the monocuspid teeth characteristic of larval jaws, indicating that jaw regeneration is not a recapitulation of development, in that an adult jaw blastema directly regenerates an adult jaw. Finally, we have studied the expression of tissue specific markers in normal and regenerating upper and lower jaws to establish whether the blastemal cells, which will form the missing part of the jaw, express any of these markers of the differentiated state, or are undifferentiated as suggested by their morphological appearance. Under our experimental conditions, no expression of markers of the differentiated state, such as those for muscle, cartilage and glands is detectable in early regenerates. On the contrary, the mesenchymal marker 22/31, whose expression in normal jaws is restricted to dermal fibroblasts and the dental pulp, is expressed in at least a half of the blastemal cells. The significance of these observations in relation to the origin of blastemal cells in the jaw will be discussed.

title: Existence of cholinephosphotransferase in mitochondria and microsomes of liver and lung of guinea pig and rat
abstract: We reported earlier on the occurrence of cholinephosphotransferase in the mitochondria of guinea pig lung. In order to determine whether organ and/or species specificities exist in regard to the cholinephosphotransferase activity in mitochondria, we have compared the subcellular distribution of the enzyme in the liver and lungs of rats and guinea pigs. Even though the activity of the enzyme was higher in microsomes than it was in mitochondria, the mitochondrial activity was authentic in both tissues of both species. The authenticity of mitochondrial activity was established by marker enzyme studies and ultrastructural examination of mitochondrial preparations.

title: Regeneration of lower and upper jaws in urodeles is differentially affected by retinoic acid.
abstract: The vitamin A derivative retinoic acid (RA) is a powerful teratogen which can induce severe craniofacial and limb malformations if administered at certain stages of gestation. In addition this compound has been shown to affect patterning in regenerating systems. A classical example is the induction of supernumerary structures along the proximodistal axis of the regenerating amphibian limb. We have investigated the effect of RA on other regenerating systems, the amphibian lower and upper jaws, both in developing and adult animals. We report here that RA does not induce formation of extra structures either in the lower or in the upper jaw of adult newts under experimental conditions where duplications of the regenerating limb occur. However, RA selectively induces severe malformations in the upper jaw regenerate that resemble those induced in avian and mammalian embryos. Analysis of the expression of the newt retinoic acid receptors RAR alpha and delta in upper and lower jaws showed that RAR alpha was expressed at a significant level in the wound epidermis, but not in blastemal cells, whereas no RAR delta could be detected in the regenerate either by in situ hybridization or by using an anti-RAR delta antibody. Therefore, unlike in the limb, in jaws RAR delta is not up-regulated following amputation, and this difference in expression may be causally related to the different effects induced by RA on jaws and limbs. In order to establish whether retinoids affected regeneration of developing jaws in a similar fashion, their effects were studied in animals whose jaws had been amputated at different developmental stages. Under the experimental conditions used overall growth retardation and head defects were observed in the majority of embryos which had been amputated and treated with retinol palmitate (RP) between stages 26-28 and 38-39. In contrast, patterning of upper jaw regenerates in larvae amputated at stage 26-28 and 38-39. In contrast, patterning of upper jaw regenerates in larvae amputated at stage 45 was not significantly affected by the treatment, although the early phase of regeneration was slower than in controls. The different responses to retinoids of regenerating facial structures in embryos, larvae and adults will be discussed.

title: Evidence for distinct fast and slow myogenic cell lineages in human foetal skeletal muscle
abstract: To analyse the myogenic cell lineages in human foetal skeletal muscle, muscle cell cultures were prepared from different foetal stages of development. The in vitro muscle cell phenotype was defined by staining the myotubes with antibodies to fast and slow skeletal muscle type myosin heavy chains using immunoperoxidase or double immunofluorescence procedures. The antibodies to fast skeletal muscle myosin heavy chains stained nearly all myotubes dark in cell cultures prepared from quadriceps muscles at 10–18 weeks of gestation. The antibodies to slow skeletal muscle myosin heavy chains, in contrast, stained only 10–40% of the myotubes very dark. The remaining myotubes were further subdivided into two populations, one of which was unstained while the other stained with variable intensity for slow myosin heavy chain. The slow myosin heavy chain staining was not influenced by the nature of the substratum used to culture these cells, although the growth of muscle cell cultures was greatly improved on matrigel-coated dishes. The presence of both slow and fast myosin heavy chains was detected even when myotubes were grown on uncoated petri dishes. The myotube diversity was further investigated by analysing the clonal populations of human foetal skeletal muscle cells in vitro. When cultured at clonal densities, two types of myogenic clones were identified by their differential staining with antibodies to slow myosin heavy chain. As was the case with the high density muscle cell cultures, virtually all myotubes in both groups of clones stained with antibodies to fast myosin heavy chains. Antibodies to slow myosin heavy chains stained nearly all myotubes dark in one group of myogenic clones, but only a subset of the myotubes stained dark for slow myosin heavy chain in the second group of clones. The proportion of slow myosin heavy chain positive myotubes in this group varied in different clones. The myogenic diversity was thus apparent in both high density and clonal human muscle cell cultures, and myogenic cells retained their ability to modify their muscle cell phenotype.

title: Glycogen content & structure & some enzymes of glycogen metabolism in human foetal organs.
abstract: The glycogen content, and its structure and the enzymes involved in glycogenolysis in human foetal organs were studied at different periods of gestation. Of all the tissues studied glycogen content was found to be the highest in cardiac muscle. Very little glycogen was present in the foetal liver at 9-12 wk of gestation, this increased progressively to nearly 2 per cent at 24 wk. Glycogen content of placenta was lower than that of skeletal muscle and liver. The level of glycogen in adipose tissue, placenta and cerebrum was not high enough to play any role in glucose homeostasis of the foetus. Human foetal liver and skeletal muscle glycogen showed the normal branched structure while the liver glycogen was found to be unusually stable. Glycogen phosphorylase activity in the foetal liver and muscle was found to be low, i.e., about a fifth and a fourth of adult liver and muscle activity respectively. The stability of foetal liver glycogen and phosphorolytic activity in the liver and muscle indicate negligible glycogenolysis during foetal development. Glucose-6-phosphatase activity in foetal liver was undetectable below 12 wk of gestation, the activity increasing progressively up to 24 wk.

title: The role of sodium dodecyl sulfate (SDS) micelles in inducing skin barrier perturbation in the presence of glycerol.
abstract: The stratum corneum (SC) serves as the skin barrier between the body and the environment. When the skin is contacted with an aqueous solution of the surfactant sodium dodecyl sulfate (SDS), a well-known model skin irritant, SDS penetrates into the skin and disrupts this barrier. It is well established, both in vitro and in vivo, that the SDS skin penetration is dose-dependent, and that it increases with an increase in the total SDS concentration above the critical micelle concentration (CMC) of SDS. However, when we added the humectant glycerol at a concentration of 10 wt% to the aqueous SDS contacting solution, we observed, through in vitro quantitative skin radioactivity assays using (14)C-radiolabeled SDS, that the dose dependence in SDS skin penetration is almost completely eliminated. To rationalize this important observation, which may also be related to the well-known beneficial effects of glycerol on skin barrier perturbation in vivo, we hypothesize that the addition of 10 wt% glycerol may hinder the ability of the SDS micelles to penetrate into the skin barrier through aqueous pores that exist in the SC. To test this hypothesis, we conducted mannitol skin permeability as well as average skin electrical resistivity measurements in vitro upon exposure of the skin to an aqueous SDS contacting solution and to an aqueous SDS + 10 wt% glycerol contacting solution in the context of a hindered-transport aqueous porous pathway model of the SC. Our in vitro studies demonstrated that the addition of 10 wt% glycerol: (i) reduces the average aqueous pore radius resulting from exposure of the skin to the aqueous SDS contacting solution from 33 +/- 5 Angstrom to 20 +/- 5 Angstrom, such that a SDS micelle of radius 18.5 +/- 1 Angstrom (as determined using dynamic light-scattering measurements) experiences significant steric hindrance and cannot penetrate into the SC, and (ii) reduces the number density of aqueous pores in the SC by more than 50%, thereby further reducing the ability of the SDS micelles to penetrate into the SC and perturb the skin barrier.

title: Mechanical phenotype is important for stromal aromatase expression
abstract: Evidence that aromatase expression in tumor-associated breast stroma is elevated, provides a rationale for use of aromatase inhibitors (AIs) in breast cancer treatment. However, regulation of local aromatase expression in cancer-free breast stroma is poorly understood. Recent clinical work indicates that stromal cells in dense breast tissue tend to express higher levels of aromatase than their counterpart from non-dense tissue. Consistent with the clinical observation, our cell culture-based study indicated that cell density, cell shape, and extracellular matrix (ECM) significantly induced stromal aromatase expression via a distinct signal transduction pathway. In addition, we identified a number of cell surface markers that are commonly associated with aromatase-expressing stromal cells. As mammographic density is one of the strongest and most prevalent risk factors for breast cancer, these findings provide a potential mechanistic link between alterations in tissue composition of dense breast tissue and increased stromal aromatase expression. Further exploration of the in vitro model system may advance understanding of an important problem in breast cancer biology.

title: Regulation of inducible gene expression by the transcription factor NF-kappaB.
abstract: The transcription factor NF-kappaB plays a critical role in regulating inducible gene expression in immune responses. The activation of NF-kappaB is regulated at multiple levels, probably reflecting a need to maintain a tight control of its activity. We have recently discovered that direct phosphorylation of NF-kappaB itself is essential for its transcriptional activity and that phosphorylation acts as a switch to determine association of nuclear NF-kappaB with histone acetylases vs deacetylases.

title: Two modes of interaction of the single-stranded DNA-binding protein of bacteriophage T7 with the DNA polymerase-thioredoxin complex.
abstract: The DNA polymerase encoded by bacteriophage T7 has low processivity. Escherichia coli thioredoxin binds to a segment of 76 residues in the thumb subdomain of the polymerase and increases the processivity. The binding of thioredoxin leads to the formation of two basic loops, loops A and B, located within the thioredoxin-binding domain (TBD). Both loops interact with the acidic C terminus of the T7 helicase. A relatively weak electrostatic mode involves the C-terminal tail of the helicase and the TBD, whereas a high affinity interaction that does not involve the C-terminal tail occurs when the polymerase is in a polymerization mode. T7 gene 2.5 single-stranded DNA-binding protein (gp2.5) also has an acidic C-terminal tail. gp2.5 also has two modes of interaction with the polymerase, but both involve the C-terminal tail of gp2.5. An electrostatic interaction requires the basic residues in loops A and B, and gp2.5 binds to both loops with similar affinity as measured by surface plasmon resonance. When the polymerase is in a polymerization mode, the C terminus of gene 2.5 protein interacts with the polymerase in regions outside the TBD. gp2.5 increases the processivity of the polymerase-helicase complex during leading strand synthesis. When loop B of the TBD is altered, abortive DNA products are observed during leading strand synthesis. Loop B appears to play an important role in communication with the helicase and gp2.5, whereas loop A plays a stabilizing role in these interactions.

title: Cell density-dependent transcriptional activation of endocrine-related genes in human adipose tissue-derived stem cells.
abstract: Adipose tissue is recognized as an endocrine organ that plays an important role in human diseases such as type II diabetes and cancer. Human adipose tissue-derived stem cells (ASCs), a distinct cell population in adipose tissue, are capable of differentiating into multiple lineages including adipogenesis. When cultured in vitro under a confluent condition, ASCs reach a commitment stage for adipogenesis, which can be further induced into terminally differentiated adipocytes by a cocktail of adipogenic factors. Here we report that the confluent state of ASCs triggers transcriptional activation cascades for genes that are responsible for the endocrine function of adipose tissue. These include insulin-like growth factor 1 (IGF-1) and aromatase (Cyp19), a key enzyme in estrogen biosynthesis. Despite similar adipogenic potentials, ASCs from different individuals display huge variations in activation of these endocrine-related genes. Bioinformatics and experimental data suggest that transcription factor Foxo1 controls a large number of "early" confluency-response genes, which subsequently induce "late" response genes. Furthermore, siRNA-mediated knockdown of Foxo1 substantially compromises the ability of committed ASCs to stimulate tumor cell migration in vitro. Thus, our work suggests that cell density is an important determinant of the endocrine potential of ASCs.