Functional cell phenotype induction with TGF-β1 and collagen-polyurethane scaffold for annulus fibrosus rupture repair

Appropriate cell sources, bioactive factors and biomaterials for generation of functional and integrated annulus fibrosus (AF) tissue analogues are still an unmet need. In the present study, the AF cell markers, collagen type I, cluster of differentiation 146 (CD146), mohawk (MKX) and smooth muscle protein 22α (SM22α) were found to be suitable indicators of functional AF cell induction. In vitro 2D culture of human AF cells showed that transforming growth factor β1 (TGF-β1) upregulated the expression of the functional AF markers and increased cell contractility, indicating that TGF-β1-pre-treated AF cells were an appropriate cell source for AF tissue regeneration. Furthermore, a tissue engineered construct, composed of polyurethane (PU) scaffold with a TGF-β1-supplemented collagen type I hydrogel and human AF cells, was evaluated with in vitro 3D culture and ex vivo preclinical bioreactor-loaded organ culture models. The collagen type I hydrogel helped maintaining the AF functional phenotype. TGF-β1 supplement within the collagen I hydrogel further promoted cell proliferation and matrix production of AF cells within in vitro 3D culture. In the ex vivo IVD organ culture model with physiologically relevant mechanical loading, TGF-β1 supplement in the transplanted constructs induced the functional AF cell phenotype and enhanced collagen matrix synthesis. In conclusion, TGF-β1-containing collagen-PU constructs can induce the functional cell phenotype of human AF cells in vitro and in situ. This combined cellular, biomaterial and bioactive agent therapy has a great potential for AF tissue regeneration and rupture repair.

Variability in the time to initiation of CPR in continuously monitored pediatric ICUs

AIM

To study the influence of patient characteristics and unit ergonomics and human factors on the time to initiation of CPR.

METHODS

A single center study of children, 0 to 21 years old, admitted to an ICU who experienced cardiopulmonary arrest (CPA) requiring >1 min of chest compressions. Time of CPA was determined by analysis of continuous ECG, plethysmography, arterial blood pressure, and end-tidal CO₂ (EtCO₂) waveforms. Initiation of CPR was identified by the onset of cyclic artifact in the ECG waveform. Patient characteristics and unit ergonomics and human factors were examined including CPA cause, identification on the High-Risk Checklist (HRC), existing monitoring, ICU type, time of day, nursing shift change, and outcome.

RESULTS

The median time from CPA to initiation of CPR was 50.5 s (IQR 26.5 to 127.5) in 36 CPAs. Forty-seven percent of patients experienced time from CPA to initiation of CPR of >1 min. There was no difference in CPA cause, ICU type, time of day, or nursing shift change.

CONCLUSION

Nearly half of pediatric patients who experienced CPA in an ICU setting did not meet AHA guidelines for early initiation of CPR. This is an opportunity to study the recognition phase of CPA using continuous monitoring data with the aim of improving the understanding of and factors contributing to delays in initiation of CPR.

Transplantation of activated nucleus pulposus cells after cryopreservation: efficacy study in a canine disc degeneration model

Transplantation of activated nucleus pulposus (NP) cells obtained by coculturing NP cells and bone marrow mesenchymal stromal cells having cell-to-cell contact has been shown to be effective in animal models and, more recently, in human clinical trials. If the NP cells can be cryopreserved, then autologous cell transplantation could be offered to patients as and when required. In a previous study, we confirmed that activated NP cells can be obtained by coculturing with mesenchymal cells after cryopreservation. However, the in vivo effects of cell transplantation therapy using activated NP cells prepared from cryopreserved cells are not known. In this in vivo canine model, we compared indicators of disc degeneration in animals that received transplanted activated normal NP cells, transplanted cryopreserved NP cells, and no cell transplantation after induction of disc degeneration. The intervertebral disc height on radiographs and T2-weighted magnetic resonance imaging were significantly higher in both cell transplantation groups compared with the degenerated disc group. Macroscopic and histological findings demonstrated attenuated disc degeneration in the two transplanted groups. Intense staining of proteoglycan and collagen type II was seen in green fluorescent protein-labelled transplanted cells, which suggested that the cells had survived and were functioning after transplantation. No significant differences were observed between the two transplanted groups. Transplanted activated cryopreserved NP cells induced a similar attenuation of intervertebral disc degeneration as that of conventionally activated NP cells. These findings suggest that the use of cryopreserved cells specific to a patient's condition has potential in transplantation therapy.

Intervertebral disc repair with activated nucleus pulposus cell transplantation: a three-year, prospective clinical study of its safety

Degeneration of the lumbar intervertebral discs is irreversible, with no treatment currently available. Building upon experimental studies that demonstrated the importance of the nucleus pulposus (NP) in preserving disc structure, we demonstrated that reinsertion of NP cells slowed further disc degeneration and that direct cell-to-cell contact co-culture with mesenchymal stromal cells (MSCs) significantly upregulated the viability of NP cells in basic and pre-clinical studies in vitro and in vivo using animal models and human cells. Here, we report a 3-year result of a prospective clinical study, aimed to assess the safety and efficacy of activated NP cell transplantation in the degenerate lumbar intervertebral disc. Candidates were 9 patients aged 20-29 years who had Pfirrmann's grade III disc degeneration at the level adjacent to the level scheduled for posterior lumbar intervertebral fusion. Viable NP cells from the fused disc were co-cultured in direct contact with autologous bone marrow-derived MSCs. One million activated NP cells were transplanted into the degenerated disc adjacent to the fused level at 7 d after the first fusion surgery. No adverse effects were observed during the 3-year follow-up period. Magnetic resonance imaging did not show any detrimental effects to the transplanted discs and revealed a mild improvement in 1 case. No cases reported any low back pain. Our clinical study confirmed the safety of activated NP cell transplantation, and the findings suggest the minimal efficacy of this treatment to slow the further degeneration of human intervertebral discs.

Fibrin-genipin adhesive hydrogel for annulus fibrosus repair: performance evaluation with large animal organ culture, in situ biomechanics, and in vivo degradation tests

Annulus fibrosus (AF) defects from annular tears, herniation, and discectomy procedures are associated with painful conditions and accelerated intervertebral disc (IVD) degeneration. Currently, no effective treatments exist to repair AF damage, restore IVD biomechanics and promote tissue regeneration. An injectable fibrin-genipin adhesive hydrogel (Fib-Gen) was evaluated for its performance repairing large AF defects in a bovine caudal IVD model using ex vivo organ culture and biomechanical testing of motion segments, and for its in vivo longevity and biocompatibility in a rat model by subcutaneous implantation. Fib-Gen sealed AF defects, prevented IVD height loss, and remained well-integrated with native AF tissue following approximately 14,000 cycles of compression in 6-day organ culture experiments. Fib-Gen repair also retained high viability of native AF cells near the repair site, reduced nitric oxide released to the media, and showed evidence of AF cell migration into the gel. Biomechanically, Fib-Gen fully restored compressive stiffness to intact levels validating organ culture findings. However, only partial restoration of tensile and torsional stiffness was obtained, suggesting opportunities to enhance this formulation. Subcutaneous implantation results, when compared with the literature, suggested Fib-Gen exhibited similar biocompatibility behaviour to fibrin alone but degraded much more slowly. We conclude that injectable Fib-Gen successfully sealed large AF defects, promoted functional restoration with improved motion segment biomechanics, and served as a biocompatible adhesive biomaterial that had greatly enhanced in vivo longevity compared to fibrin. Fib-Gen offers promise for AF repairs that may prevent painful conditions and accelerated degeneration of the IVD, and warrants further material development and evaluation.

Cell therapy for intervertebral disc repair: advancing cell therapy from bench to clinics

Intervertebral disc (IVD) degeneration is a major cause of pain and disability; yet therapeutic options are limited and treatment often remains unsatisfactory. In recent years, research activities have intensified in tissue engineering and regenerative medicine, and pre-clinical studies have demonstrated encouraging results. Nonetheless, the translation of new biological therapies into clinical practice faces substantial barriers. During the symposium "Where Science meets Clinics", sponsored by the AO Foundation and held in Davos, Switzerland, from September 5-7, 2013, hurdles for translation were outlined, and ways to overcome them were discussed. With respect to cell therapy for IVD repair, it is obvious that regenerative treatment is indicated at early stages of disc degeneration, before structural changes have occurred. It is envisaged that in the near future, screening techniques and non-invasive imaging methods will be available to detect early degenerative changes. The promises of cell therapy include a sustained effect on matrix synthesis, inflammation control, and prevention of angio- and neuro-genesis. Discogenic pain, originating from "black discs" or annular injury, prevention of adjacent segment disease, and prevention of post-discectomy syndrome were identified as prospective indications for cell therapy. Before such therapy can safely and effectively be introduced into clinics, the identification of the patient population and proper standardisation of diagnostic parameters and outcome measurements are indispensable. Furthermore, open questions regarding the optimal cell type and delivery method need to be resolved in order to overcome the safety concerns implied with certain procedures. Finally, appropriate large animal models and well-designed clinical studies will be required, particularly addressing safety aspects.

CCL5/RANTES is a key chemoattractant released by degenerative intervertebral discs in organ culture

Release of chemotactic factors in response to tissue damage has been described for different musculoskeletal tissues, including the intervertebral disc (IVD). This study investigated the chemoattractants that are released by induced degenerative IVDs and may be involved in recruiting mesenchymal stem cells (MSCs). Bovine caudal discs were cultured within a bioreactor and loaded under conditions that mimicked physiological or degenerative settings. Between days 4-6, medium was replaced by PBS, which was subsequently used for proteomic, ELISA and immunoprecipitation analyses of secreted chemokines and cytokines. A Boyden chamber assay was used to observe human MSC migration towards native and chemokine depleted media. Gene expression levels of chemokine receptors in human MSCs were analysed, and CCL5 was localised in bovine and human IVD by immunohistochemistry. Proteomic analysis revealed the presence of CCL5 and CXCL6 within conditioned media. Higher concentrations of CCL5 were found in the degenerative media, and a relationship was found between interleukin-1β and CCL5 concentration. Chemokine immunoprecipitation showed that MSCs had a significantly reduced chemotactic migration towards CCL5-immunoprecipitated and CCL5/CXCL6 co-immunoprecipitated media, whilst CXCL6 depletion did not change MSC chemotaxis. MSCs showed a significant increase in mRNA expression of the CCL5 receptors, CCR1 and CCR4, upon culture in degenerative media. Furthermore, CCL5 was identified in bovine and human disc tissue by immunohistochemistry. Hence, CCL5 may be a key chemoattractant that is produced and released by the intervertebral disc cells. Therefore, these factors could be used to enhance stem/progenitor cell mobilisation in regenerative therapies for early stages of disc degeneration.

Variations in gene and protein expression in human nucleus pulposus in comparison with annulus fibrosus and cartilage cells: potential associations with aging and degeneration

OBJECTIVE

Regardless of recent progress in the elucidation of intervertebral disc (IVD) degeneration, the basic molecular characteristics that define a healthy human IVD are largely unknown. Although work in different animal species revealed distinct molecules that might be used as characteristic markers for IVD or specifically nucleus pulposus (NP) cells, the validity of these markers for characterization of human IVD cells remains unknown.

DESIGN

Eleven potential marker molecules were characterized with respect to their occurrence in human IVD cells. Gene expression levels of NP were compared with annulus fibrosus (AF) and articular cartilage (AC) cells, and potential correlations with aging were assessed.

RESULTS

Higher mRNA levels of cytokeratin-19 (KRT19) and of neural cell adhesion molecule-1 were noted in NP compared to AF and AC cells. Compared to NP cytokeratin-18 expression was lower in AC, and alpha-2-macroglobulin and desmocollin-2 lower in AF. Cartilage oligomeric matrix protein (COMP) and glypican-3 expression was higher in AF, while COMP, matrix gla protein (MGP) and pleiotrophin expression was higher in AC cells. Furthermore, an age-related decrease in KRT19 and increase in MGP expression were observed in NP cells. The age-dependent expression pattern of KRT19 was confirmed by immunohistochemistry, showing the most prominent KRT19 immunoreaction in the notochordal-like cells in juvenile NP, whereas MGP immunoreactivity was not restricted to NP cells and was found in all age groups.

CONCLUSIONS

The gene expression of KRT19 has the potential to characterize human NP cells, whereas MGP cannot serve as a characteristic marker. KRT19 protein expression was only detected in NP cells of donors younger than 54 years.

Low-intensity pulsed ultrasound stimulates cell proliferation, proteoglycan synthesis and expression of growth factor-related genes in human nucleus pulposus cell line

Low-intensity pulsed ultrasound (LIPUS) stimulation has been shown to effect differentiation and activation of human chondrocytes. A study involving stimulation of rabbit disc cells with LIPUS revealed upregulation of cell proliferation and proteoglycan (PG) synthesis. However, the effect of LIPUS on human nucleus pulposus cells has not been investigated. In the present study, therefore, we investigated whether LIPUS stimulation of a human nucleus pulposus cell line (HNPSV-1) exerted a positive effect on cellular activity. HNPSV-1 cells were encapsulated in 1.2% sodium alginate solution at 1x10(5) cells/ml and cultured at 10 beads/well in 6-well plates. The cells were stimulated for 20 min each day using a LIPUS generator, and the effects of LIPUS were evaluated by measuring DNA and PG synthesis. Furthermore, mRNA expression was analyzed by cDNA microarray using total RNA extracted from the cultured cells. Our study revealed no significant difference in cell proliferation between the control and the ultrasound treated groups. However, PG production was significantly upregulated in HNPSV cells stimulated at intensities of 15, 30, 60, and 120 mW/cm(2) compared with the control. The results of cDNA array showed that LIPUS significantly stimulated the gene expression of growth factors and their receptors (BMP2, FGF7, TGFbetaR1 EGFRF1, VEGF). These findings suggest that LIPUS stimulation upregulates PG production in human nucleus pulposus cells by the enhancement of several matrix-related genes including growth factor-related genes. Safe and non-invasive stimulation using LIPUS may be a useful treatment for delaying the progression of disc degeneration.

Stem cell applications in intervertebral disc repair

There is increasing rise of interest in stem cell therapy, as it provides new options for treating a broad range of diseases. Several experimental methods are being explored for the use of stem cells in delaying or reversing the degenerative process of the intervertebral disc, a major cause of low back pain. In this article, we review the current strategies for stem cell applications in intervertebral disc repair and present three novel approaches. These are, first, the activation of nucleus pulposus cells by co-culture with mesenchymal stem cells for autologous disc cell reinsertion; second, the in vitro induction of nucleus pulposus-like or annulus fibrosus-like cells from mesenchymal stem cells; and third, the in vivo induction study by direct transplantation of mesenchymal stem cells to the intervertebral disc induced to degenerate experimentally. Although still untested, stem cell therapy may become a major option in the treatment of intervertebral disc degeneration.

Cross talk between Smad transcription factors and TNF-alpha in intervertebral disc degeneration

The transforming growth factor-beta (TGF-beta) and the tumor necrosis factor-alpha (TNF-alpha) families are known to play important roles in intervertebral disc degeneration (IVD). However, molecular interactions between the TGF-beta and TNF-alpha signaling pathways have yet to be elucidated. The purpose of this study was to analyze the expression patterns of Smad transcription factor signaling associated with IVDs with aging and to examine the modulation of Smad signaling by TNF-alpha in IVD cells using SD rats. According to these experimental results, BMP signals in the TGF-beta family were more likely to be a key factor in IVD degeneration by aging, and it was predicted that besides the involvement of catabolic factors like MMPs and ADAMS-TS, there may be a decrease in expression of anabolic factors through cross talk of signaling between TNF-alpha and TGF-beta pathway in pathogenesis of disc degeneration.

Expression of CD90 on keratinocyte stem/progenitor cells

BACKGROUND

The identification and purification of keratinocyte stem cells (KSCs) that are capable of self-renewal and maintenance of differentiating cell populations could contribute both to our understanding of the biology of these cells, and to significant clinical applications, such as the culturing of keratinocytes for transplantation to severe burn wounds. Here, we report the detection of CD90(+) cells in cultured normal human epidermal keratinocytes and adult skin.

OBJECTIVES

To investigate the biological function of CD90(+) and CD90(-) keratinocytes.

METHODS

CD90(+) and CD90(-) keratinocytes were purified from adult skin and cultured keratinocytes using fluorescent activated cell sorting, and their biological abilities were analysed using both in vitro and in vivo assays.

RESULTS

Flow cytometry (FCM) analysis identified approximately 18% of post-primary neonatal keratinocytes as CD90(+). However, during expansion of the culture, the expression level of CD90 rapidly decreased to about 2.5% at passage 10, while most of the keratinocytes maintained expression of alpha6 integrin. Purified CD90(+) keratinocytes demonstrated a sixfold higher cell growth rate than CD90(-) cells and the ability to form large (over 3 mm in diameter) colonies. We then quantitatively evaluated both populations using a previously described in vivo human epidermal cyst formation assay. Enhanced green fluorescent protein (EGFP)-labelled CD90(+) or CD90(-) keratinocytes were subcutaneously injected into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Six weeks after transplantation, EGFP(+) cell clusters in human epidermal cysts were evaluated using image analysis software. EGFP(+) cell cluster areas in the basal layer, derived from EGFP(+) CD90(+) cells, were eightfold larger than clusters of EGFP(+) CD90(-) cells. Furthermore, immunohistochemical staining and FCM analysis indicated that CD90 was expressed in most of the basal layer of the normal human epidermis.

CONCLUSIONS

These results indicated that CD90 is a useful marker for the detection of human KSC-enriched populations in cultured human keratinocytes.

Analysis of the pilU gene for the prepilin peptidase involved in the biogenesis of type IV pili encoded by plasmid R64

In many type IV pili, the N-terminal amino acid of the pilin subunit is N-methylated phenylalanine. A prepilin peptidase removes the leader peptide from the precursor and methylates the amino group of the newly formed phenylalanine. PilS, the precursor of the pilin encoded by plasmid R64, is processed by the prepilin peptidase PilU, but the N-terminal amino acid of the mature pilin is a non-methylated tryptophan that is otherwise modified. To study the relationship between the structure and function of PilU, 42 missense pilU mutations were constructed by PCR and site-directed mutagenesis, and the ability of these pilU mutants to complement a pilU null mutant for mating in liquid culture was analyzed. Although practically no conjugation was noted for 21 of the mutants, the remaining 21 supported varying levels of residual plasmid transfer activity. Two mutants with aspartic acid replacements in conserved motifs exhibited no PilU activity, suggesting that the product of the pilU gene is an aspartic acid peptidase, like TcpJ, the prepilin peptidare of Vibrio cholerae. No PilS processing was detected in 21 of the mutants, but the remaining 21 exhibited varying levels of residual PilS processing. A close correlation was noted between residual PilS processing activity and conjugative transfer, suggesting that the pilU gene product possesses prepilin peptidase activity, but is unable to methylate the N-terminal tryptophan. Based on the activity of pilU-phoA and pilU-lacZ fusion genes encoding different segments of PilU, a model for the membrane topology of the protein is also proposed. Furthermore, some amino acid substitutions in the pilU portion of the pilU-phoA and pilU-lacZ fusion genes were found to alter the membrane topology of the product.

Atpase activity and multimer formation of Pilq protein are required for thin pilus biogenesis in plasmid R64

Plasmid R64 pilQ gene is essential for the formation of thin pilus, a type IV pilus. The pilQ product contains NTP binding motifs and belongs to the PulE-VirB11 family of NTPases. The pilQ gene was overexpressed with an N-terminal His tag, and PilQ protein was purified. Purified His tag PilQ protein displayed ATPase activity with a V(max) of 0.71 nmol/min/mg of protein and a K(m) of 0.26 mm at pH 6.5. By gel filtration chromatography, PilQ protein was eluted at the position corresponding to 460 kDa, suggesting that PilQ protein forms a homooctamer. To analyze the relationship between structure and function of PilQ protein, amino acid substitutions were introduced within several conserved motifs. Among 11 missense mutants, 7 mutants exhibited various levels of reduced DNA transfer frequencies in liquid matings. Four mutant genes (T234I, K238Q, D263N, and H328A) were overexpressed with a His tag. The purified mutant PilQ proteins contained various levels of reduced ATPase activity. Three mutant PilQ proteins formed stable multimers similar to wild-type PilQ, whereas the PilQ D263N multimer was unstable. PilQ D263N monomer exhibited low ATPase activity, while PilQ D263N multimer did not. These results indicate that ATPase activity of the PilQ multimer is essential for R64 thin pilus biogenesis.

Role for cGATA-5 in transcriptional regulation of the embryonic chicken pepsinogen gene by epithelial-mesenchymal interactions in the developing chicken stomach

A gene encoding embryonic chicken pepsinogen (ECPg), a zymogen of the digestive enzyme pepsin, is expressed specifically in epithelial cells of glands of embryonic stage proventriculus (glandular stomach) under the influence of mesenchyme. We found four GATA and one Sox binding motifs in 1.1 kb of the 5' flanking region of the ECPg gene which are essential to the organ-specific expression of the gene. The expression of cGATA-5 and cSox2 in the proventriculus from day 6 to day 12 of incubation was therefore analyzed. cGATA-5 was more strongly expressed in glandular epithelial cells than in luminal epithelial cells, while cSox2 gene expression was weaker in glandular epithelial cells. Using heterologous recombination explants we also discovered that the expression of cGATA-5 and cSox2 in epithelial cells was affected by mesenchyme when the latter induced ECPg gene expression in epithelial cells. Introduction of expression constructs into epithelial cells by electroporation demonstrated that cGATA-5 upregulated transcription of a reporter luciferase gene via a cis element in the 5' flanking region of the ECPg gene. The gel mobility shift assay revealed that the cGATA-5 protein specifically binds to the GATA binding sites. cSox2 downregulated the activity of luciferase but it was not through the Sox binding motif. These results suggest that cGATA-5 positively regulates transcription of the ECPg gene and is involved in spatial regulation of the pepsinogen gene during development.

Ileal carcinoid tumor complicating carcinoid heart disease and secondary retroperitoneal fibrosis

A 70-year-old man with metastatic liver tumors showed carcinoid syndrome with clinical symptoms of facial flushing, palpitation, dyspnea, and an itching sensation. Regurgitation of the tricuspid and aortic valves was observed by echocardiography. An elevated serum level of serotonin and a high urine excretion of serotonin metabolites were confirmed. Autopsy confirmed a serotonin-immunoreactive 1 cm ileal carcinoid tumor with metastasis to the liver, bone and peritoneum. The tumor cells were argyrophilic but not argentaffin, and showed erythrophagocytosis in the primary lesion. All the four heart valves and bilateral atrial endocardium showed fibromyxoid thickening, indicating the association of carcinoid heart disease. Desmoplastic reaction with deposition of sulfated acid mucopolysaccharides was also observed in the retroperitoneal space (secondary retroperitoneal fibrosis). Stenosis of the bilateral ureters and inferior mesenteric artery provoked hydronephrosis and lethal ischemic necrosis of the left-sided colon, respectively. Rarity of functioning ileal carcinoid tumor and pathogenesis of systemic fibroplasia are discussed.

Reconstitution of damage DNA excision reaction from SV40 minichromosomes with purified nucleotide excision repair proteins

We previously constructed the cell-free nucleotide excision repair (NER) assay system with UV-irradiated SV40 minichromosomes to analyze the mechanism of NER reaction on chromatin DNA. Here we investigate the factor that acts especially on nucleosomal DNA during the damage excision reaction, and reconstitute the damage excision reaction on SV40 minichromosomes. NER-proficient HeLa whole cell extracts were fractionated, and the amounts of known NER factors involved in the column fractions were determined by immunoblot analyses. The column fractions were quantitatively and systematically replaced by highly purified NER factors. Finally, damage DNA excision reaction on SV40 minichromosomes was reconstituted with six highly purified NER factors, XPA, XPC-HR23B, XPF-ERCC1, XPG, RPA and TFIIH, as those essential for the reaction with naked DNA. Further analysis showed that the damages on chromosomal DNA were excised as the same efficiency as those on naked DNA for short incubation. At longer incubation time, however, the damage excision efficiency on nucleosomal DNA was decreased whereas naked DNA was still vigorously repaired. These observations suggest that although the six purified NER factors have a potential to eliminate the damage DNA from SV40 minichromosomes, the chromatin structure may still have some repressive effects on NER.

The pilL and pilN genes of IncI1 plasmids R64 and ColIb-P9 encode outer membrane lipoproteins responsible for thin pilus biogenesis

The predicted amino acid sequences of the pilL and pilN genes, required for the thin pilus formation of IncI1 plasmids R64 and ColIb-P9, contain N-terminal lipoprotein signal peptide motifs. The pilL and pilN products were labeled with [(3)H]palmitic acid as 38- and 57-kDa proteins, respectively, indicating that they are lipoproteins. Both PilL and PilN were localized to the outer membrane.

Osteoclast molecular phenotyping by random cDNA sequencing

The osteoclast is a cell type that is highly specialized for its bone resorption function. In order to decipher the numerous biochemical functions of osteoclasts, a description of the gene expression profile of osteoclasts would be beneficial. We have sought to identify genes that are highly expressed in osteoclasts by partially sequencing 194 randomly chosen cDNA clones from a representative rabbit osteoclast cDNA library. Comparison to nucleic acid and protein sequence databases indicates that 135 of these cDNAs are identical to or homologous to known mammalian genes. Reverse transcription-polymerase chain reaction (RT-PCR) assays with microisolated osteoclasts were used to verify the osteoclast expression of some of these genes. Fifty-nine cDNAs, including two abundantly expressed species, have no significant similarity to the sequence databases and likely represent novel genes. The most abundant of the osteoclast expressed genes encode cofilin and the vacuolar H(+)-ATPase 16 kd subunit. Each were represented at a frequency of 4.1% of the clones in the library (95% confidence interval = 2.4-6.6%). The high expression of these gene products is consistent with the high motility of osteoclasts and their very active hydrogen ion secretion. Other abundantly expressed sequences include beta-actin (95% C.I. = 2.0-6.0%), creatine kinase B (95% C.I. = 1.2-4.9%), c-fms and ribosomal protein L18 (95% C.I. = 0.8-4.3%), and cathepsin-OC2, cyclophilin, delta-aminolevulinate synthetase, 16S mitochondrial rRNA, and two novel gene sequences (95% C.I. = 0.5-3.6%).

The mouse Eb meiotic recombination hotspot contains a tissue-specific transcriptional enhancer

A meiotic recombination hotspot exists within the second intron of the mouse major histocompatibility complex (MHC) gene, Eb. In the present study, a small fragment from the intron which contains two potential transcriptional regulatory elements was cloned into an expression vector and its effect on transcription was tested. This fragment was found to contain tissue-specific transcriptional enhancer activity. An octamer-like sequence and a B motif may contribute to this enhancer activity. Similar regulatory sequences with the same orientation and distance from one another are found in another mouse MHC recombination hotspot.

Reversible denaturation of the estrogen receptor and estimation of polypeptide chain molecular weight

The estrogen receptor protein loses its ability to bind to estrogens upon denaturation with sodium dodecyl sulfate and 2-mercaptoethanol. Binding activity is recovered at 60-80% efficiency upon removal of the denaturants, equilibration with 6 M guanidine hydrochloride, and dilution into buffer containing estrogen. Renatured receptor is similar to native receptor in affinity for 17 beta-estradiol and ability to bind DNA. Detection of receptor activity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of uterine or pituitary cytosol or of uterine nuclear extracts reveals a single unique polypeptide species of 65,000 mol wt.