Axonal regrowth is impaired during digit tip regeneration in mice

Mice are intrinsically capable of regenerating the tips of their digits after amputation. Mouse digit tip regeneration is reported to be a peripheral nerve-dependent event. However, it is presently unknown what types of nerves and Schwann cells innervate the digit tip, and to what extent these cells regenerate in association with the regenerative response. Given the necessity of peripheral nerves for mammalian regeneration, we investigated the neuroanatomy of the unamputated, regenerating, and regenerated mouse digit tip. Using immunohistochemistry for β-III-tubulin (β3T) or neurofilament H (NFH), substance P (SP), tyrosine hydroxylase (TH), myelin protein zero (P0), and glial fibrillary acidic protein (GFAP), we identified peripheral nerve axons (sensory and sympathetic), and myelinating- and non-myelinating-Schwann cells. Our findings show that the digit tip is innervated by two digital nerves that each bifurcate into a bone marrow (BM) and connective tissue (CT) branch. The BM branches are composed of sympathetic axons that are ensheathed by non-myelinating-Schwann cells whereas the CT branches are composed of sensory and sympathetic axons and are ensheathed by myelinating- and non-myelinating-Schwann cells. The regenerated digit neuroanatomy differs from unamputated digit in several key ways. First, there is 7.5 fold decrease in CT branch axons in the regenerated digit compared to the unampuated digit. Second, there is a 5.6 fold decrease in myelinating-Schwann cells in the regenerated digit compared to the unamputated digit that is consistent with the decrease in CT branch axons. Importantly, we also find that the central portion of the regenerating digit blastema is aneural, with axons and Schwann cells restricted to peripheral and distal blastema regions. Finally, we show that even with impaired innervation, digits maintain the ability to regenerate after re-amputation. Taken together, these data indicate that nerve regeneration is impaired in the context of mouse digit tip regeneration.     

Glucocorticoid receptor binding in twin pairs is affected by shared environment but not by shared genes

We set out to determine whether glucocorticoid receptor activity is affected mainly by genetic or environmental factors. The affinity and capacity of the glucocorticoid receptor was measured using dexamethasone binding in whole leukocytes from 53 monozygotic and 48 dizygotic twin pairs. Receptor binding characteristics assayed from twin pairs on the same day were highly correlated within twin pairs irrespective of zygosity. Apparent Kd was negatively correlated with environmental temperature (R²=0.13, P<0.0001) but this did not confound the intra-pair correlation, suggesting a strong familial component independent of zygosity. Receptor binding parameters were not more closely correlated in monozygotic twins than dizygotic twin pairs indicating that there is no major genetic contribution to receptor binding and that environmental influences predominate. The close similarity in binding between twin pairs in adulthood raises the possibility that familial, non-genetic, factors such as shared early life environment may programme the glucocorticoid receptor.     

Nerve regeneration through synthetic biodegradable nerve guides: regulation by the target organ

The successful regeneration of a multifascicular, complete peripheral nerve through a tubular synthetic biodegradable nerve guide across a gap of 10 mm in the rat sciatic nerve is reported. The importance of the distal nerve as a source of target-derived neuronotrophic factors necessary for the successful regeneration of the proximal regenerating nerve is emphasized. A simplified research model for further investigation into and manipulation of the biological processes of nerve regeneration is described. The potential clinical utilization of this model in the management of peripheral nerve injuries and, ultimately, central nervous system lesions is mentioned.     

Dimerization drives PDGF receptor endocytosis through a C-terminal hydrophobic motif shared by EGF receptor

Like many other receptor tyrosine kinases (RTKs), platelet-derived growth factor (PDGF) receptor β (PDGFR-β) is internalized and degraded in lysosomes in response to PDGF stimulation, which regulates many aspects of cell signalling. However, little is known about the regulation of PDGFR-β endocytosis. Given that ligand binding is essential for the rapid internalization of RTKs, the events induced by the ligand binding likely contribute to the regulation of ligand-induced RTK internalization. These events include receptor dimerization, activation of intrinsic tyrosine kinase activity and autophosphorylation. In this communication, we examined the role of PDGFR-β kinase activity, PDGFR-β dimerization and PDGFR-β C-terminal motifs in PDGF-induced PDGFR-β internalization. We showed that inhibition of PDGFR-β kinase activity by chemical inhibitor or mutation did not block PDGF-induced PDGFR-β endocytosis, suggesting that the kinase activity is not essential. We further showed that dimerization of PDGFR-β is essential and sufficient to drive PDGFR-β internalization independent of PDGFR-β kinase activation. Moreover, we showed that the previously reported 14 amino acid sequence 952-965 is required for PDGF-induced PDGFR-β internalization. Most importantly, we showed that this PDGFR-β internalization motif is exchangeable with the EGFR internalization motif (1005-1017) in mediating ligand-induced internalization of both PDGFR-β and EGFR. This indicates a common mechanism for the internalization of both PDGFR-β and EGFR.     

Nerve commitment during head regeneration in hydra.

Most important event in head regeneration in hydra is a wave of conversion of many interstitial cells into nerve cells. Experimental evidence lends support to the idea that the commitment of interstitial cells into nerve cells is the first morphogenetic prerequisite for emergence of head structures, when the number of nerve cells increases. This increase in nerve cells is delayed when regeneration occurs at a site lower in the body column.     

Nerve regeneration with aid of nanotechnology and cellular engineering

Repairing nerve defects with large gaps remains one of the most operative challenges for surgeons. Incomplete recovery from peripheral nerve injuries can produce a diversity of negative outcomes, including numbness, impairment of sensory or motor function, possibility of developing chronic pain, and devastating permanent disability. In the last few years, numerous microsurgical techniques, such as coaptation, nerve autograft, and different biological or polymeric nerve conduits, have been developed to reconstruct a long segment of damaged peripheral nerve. A few of these techniques are promising and have become popular among surgeons. Advancements in the field of tissue engineering have led to development of synthetic nerve conduits as an alternative for the nerve autograft technique, which is the current practice to bridge nerve defects with gaps larger than 30 mm. However, to date, despite significant progress in this field, no material has been found to be an ideal alternative to the nerve autograft. This article briefly reviews major up-to-date published studies using different materials as an alternative to the nerve autograft to bridge peripheral nerve gaps in an attempt to assess their ability to support and enhance nerve regeneration and their prospective drawbacks, and also highlights the promising hope for nerve regeneration with the next generation of nerve conduits, which has been significantly enhanced with the tissue engineering approach, especially with the aid of nanotechnology in development of the three-dimensional scaffold. The goal is to determine potential alternatives for nerve regeneration and repair that are simply and directly applicable in clinical conditions.     

Salmonella regrowth in compost as influenced by substrate (salmonella regrowth in compost)

Composting can eliminate pathogenic organisms, including salmonellae, from sewage sludge. However, if salmonellae are present in the compost at undetectable levels or are inoculated into the compost by infected animals or from other sources, they may regrow presenting a health hazard for certain uses of compost. In this study, we examined dilute mineral-salt extracts of three composts from widely separate composting sites in the United States and found that they supported growth ofSalmonella typhimurium. From kinetic studies of the growth of the organism on these extracts, we concluded that each compost produced on extraction a single water-soluble substrate and that the substrates from the different composts were very similar, if not identical.We thank J. Robert Burge, Statistical Consulting and Analysis, ARS, USDA for invaluable help with the statistical analyses, and Alice V. Gibson of our laboratory for technical help.     

Visceral regeneration in the crinoid Antedon mediterranea: basic mechanisms, tissues and cells involved in gut regrowth

Crinoids are able to regenerate completely many body parts, namely arms, pinnules, cirri, and also viscera, including the whole gut, lost after self-induced or traumatic mutilations. In contrast to the regenerative processes related to external appendages, those related to internal organs have been poorly investigated. In order to provide a comprehensive view of these processes, and of their main events, timing and mechanisms, the present work is exploring visceral regeneration in the feather star Antedon meditteranea. The histological and cellular aspects of visceral regeneration were monitored at predetermined times (from 24 hours to 3 weeks post evisceration) using microscopy and immunocytochemistry. The overall regeneration process can be divided into three main phases, leading in 3 weeks to the reconstruction of a complete functional gut. After a brief wound healing phase, new tissues and organs develop as a result of extensive cell migration and transdifferentiation. The cells involved in these processes are mainly coelothelial cells, which after trans-differentiating into progenitor cells form clusters of enterocytic precursors. The advanced phase is then characterized by the growth and differentiation of the gut rudiment. In general, our results confirm the striking potential for repair (wound healing) and regeneration displayed by crinoids at the organ, tissue and cellular levels.     

Convergent mechanisms for recognition of divergent cytokines by the shared signaling receptor gp130

Gp130 is a shared cell-surface signaling receptor for at least ten different hematopoietic cytokines, but the basis of its degenerate recognition properties is unknown. We have determined the crystal structure of human leukemia inhibitory factor (LIF) bound to the cytokine binding region (CHR) of gp130 at 2.5 A resolution. Strikingly, we find that the shared binding site on gp130 has an entirely rigid core, while the LIF binding interface diverges sharply in structure and chemistry from that of other gp130 ligands. Dissection of the LIF-gp130 interface, along with comparative studies of other gp130 cytokines, reveal that gp130 has evolved a "thermodynamic plasticity" that is relatively insensitive to ligand structure, to enable crossreactivity. These observations reveal a novel and alternative mechanism for degenerate recognition from that of structural plasticity.     

Studies onSargassum II. Quantitative ultrastructural changes in differentiated stipe cells during wound regeneration and regrowth

Summary Quantitative electron micrograph analytical techniques were used to study cytological changes associated with the process of dedifferentiation and redifferentiation in mature, specialized cells of the stipe in the brown algaSargassum filipendula following wounding. Early cytological changes associated with this process appear to be those involved with formation of a protective layer of material at the wound surface. An increase in the volume of cytoplasm occupied by mitochondria, dictyosomes, and type A and B vesicles was evident by three days postwound. Cytoplasmic volume occupied by chloroplasts decreased during the early stages of wound reaction while the development of internal membranes (thylakoids) in these organelles increased. Cells at the cut surface eventually differentiated into one of two types of tissues: 1. A wound surface epidermal layer similar in cytological aspect to the epidermal layers of the intact and regenerated plant. 2. A meristematic regeneration bud from which developed the blade-like regeneration growth. The morphology and anatomy of the tissues of the regeneration blade resembled those of the blade of the intact plant rather than those of the stipe from which it originated. Percent difference values were obtained by comparing cytological features of the tissues from the regeneration blade with those of the intact stipe and blade. The comparisons supported previously obtained data indicating that the regeneration blade should be considered as a typical blade organ rather than a morphological variant of the stipe. Results of this study raises questions about possible physiological differences which may exist between stipe and blade organs in this plant.     

An anti-interferon activity shared by paramyxovirus C proteins: Inhibition of Toll-like receptor 7/9-dependent alpha interferon induction

Paramyxovirus C protein targets the host interferon (IFN) system for virus immune evasion. To identify its unknown anti-IFN activity, we examined the effect of Sendai virus C protein on activation of the IFN-α promoter via various signaling pathways. This study uncovers a novel ability of C protein to block Toll-like receptor (TLR) 7- and TLR9-dependent IFN-α induction, which is specific to plasmacytoid dendritic cells. C protein interacts with a serine/threonine kinase IKKα and inhibits phosphorylation of IRF7. This anti-IFN activity of C protein is shared across genera of the Paramyxovirinae, and thus appears to play an important role in paramyxovirus immune evasion.