The Fetal Dermal but Not Loose Fascial Mesenchymal Cells Possess Regenerative Activity of Dermal Structure

Fetal skin possesses a regenerative activity until certain developmental stages. However, the origin of cells that regenerate dermis after wounding has not been clarified yet. In the present study we located the origin of cells that reconstruct fetal dermal structure by histological examination and by marking cells in the loose fascia. Next we evaluated the regenerative activity of fetal dermal mesenchymal cells by cotransplanting with fetal epidermal cells onto the skin defect of scid mice. We conclude that fetal dermal mesenchymal cells but not loose fascial cells possess regenerative activity even on the environment in scid mice.

Irx3 and Bmp2 regulate mouse mesenchymal cell chondrogenic differentiation in both a Sox9-dependent and -independent manner

Sox9, a master regulator of cartilage development, controls the cell fate decision to differentiate from mesenchymal to chondrogenic cells. In addition, Sox9 regulates the proliferation and differentiation of chondrocytes, as well as the production of cartilage-specific proteoglycans. The existence of Sox9-independent mechanisms in cartilage development remains to be determined. Here, we attempted to identify genes involved in such putative mechanisms via microarray analysis using a mouse chondrogenic cell line, N1511. We first focused on transcription factors that exhibited upregulated expression following Bmp2 treatment, which was not altered by subsequent treatment with Sox9 siRNA. Among these, we selected positive regulators for chondrogenesis and identified Iroquois-related homeobox 3 (Irx3) as one of the candidate genes. Irx3 expression gradually increased with chondrocyte terminal differentiation in a reciprocal manner to Sox9 expression, and promoted the chondrogenic differentiation of mesenchymal cells upon Bmp2 treatment. Furthermore, Irx3 partially rescued impaired chondrogenesis by upregulating the expression of epiphycan and lumican under reduced Sox9 expression. Finally, Irx3 was shown to act in concert with Bmp2 signaling to activate the p38 MAPK pathway, which in turn stimulated Sox9 expression, as well as the expression of epiphycan and lumican in a Sox9-independent manner. These results indicate that Irx3 represents a novel chondrogenic factor of mesenchymal cells, acts synergistically with Bmp2-mediated signaling, and regulates chondrogenesis independent of the transcriptional machinery associated with Sox9-mediated regulation.

E-cadherin expression in the subepithelial nevus cells of the giant congenital nevocellular nevi (GCNN) correlates with their migration ability in vitro

BACKGROUND

Giant congenital nevocellular nevi (GCNN) are histologically characterized by the broad distribution of nevus cells in the epidermis and dermis.

OBJECTIVE

To characterize E-cadherin in GCNN and define its role in nevic cell migrations.

METHODS

Twenty-four cases were immunohistochemically examined and in five cases cells were isolated for primary culture for migration assays.

RESULTS

The nevus cells in the superficial region showed the immunoreactivity of E-cadherin in a membranous pattern, but those in the deep part of dermis had little immunoreactivity. Ultra-structural analysis of the superficial nevus cells revealed that E-cadherin immunodeposits in the fibrillar processes around the cell body in a spotted pattern. This distribution pattern is quite different from that in the adherens junction of skin squamous epithelial cells. Boyden chamber experiments were performed using primary cultures of intradermal nevus cells. EDTA pretreatment reduced cell migration to the E-cadherin positive side when the E-cadherin positive population was relatively large in the primary cultures.

CONCLUSIONS

These results indicate that E-cadherin in the nevus cells may affect nevus cell motility rather than intercellular attachment.

Amelogenin positive cells scattered in the interstitial component of odontogenic fibromas

BACKGROUND

Odontogenic tumours are often biphasic, consisting of epithelial and interstitial components, with an origin that is not well understood. Odontogenic fibromas are rich in mesenchymal component, but also have many epithelial nests.

AIMS

To investigate the origin of this tumour by immunohistochemistry.

METHODS

The expression of several odontogenic and epithelial markers, including amelogenin, was investigated by immunofluorescent studies.

RESULTS

Immunohistochemical analysis showed that epithelial nests exhibited E-cadherin expression, but not amelogenin. Amelogenin positive cells were scattered in the fibrous tissue, which did not exhibit epithelial marker expression except for epithelial membrane antigen. In one case that had received a test biopsy before whole resection of tumour, amelogenin positive cells were distributed in the regenerating mucosal epithelium or subepithelial tissue.

CONCLUSIONS

Results indicate that amelogenin positive cells of odontogenic fibromas have an epithelial origin and may have the potential for epithelial mesenchymal transition, which has not to date been investigated in benign tumours.

The expression of chicken NOV, a member of the CCN gene family, in early stage development

The nephroblastoma overexpressed gene, NOV, is a member of the CCN gene family. We investigated the NOV gene expression pattern in the chicken during early stage embryogenesis. Several embryonic structures showed a distinct expression pattern. The initial expression was detected in Hensen's node (Hamburger and Hamilton stage (HH) 5). The expression was noted in the presumptive notochord and floor plate forming cells. The expression on the left side was more elongated posteriorly, a type of left-right asymmetry. Chicken NOV gene expression in the forming notochord and floor plate was observed until HH 18. The expression was also detected in the ventral area of the mesencephalon and isthmus at HH 14-16.

Arthoscopic diagnosis of partial scapholunate ligament tears as a cause of radial sided wrist pain in patients with inconclusive x-ray and MRI findings

To clarify the pathology of radial-sided wrist pain with inconclusive X-ray and MRI findings, we performed arthroscopic examinations of 11 wrists in 10 patients. Physical examination and various image investigations could not identify the cause of the pain. Arthroscopy revealed partial to complete tears of the scapho-lunate interosseous ligament and synovitis and/or chondral bone defects at the scaphotrapezio-trapezoidal joint in all 11 wrists. Surgical procedures consisted of eight simple synovectomies, two ligament reconstructions and one percutaneous pinning. Pain relief was achieved in 10 wrists. One wrist which had a simple synovectomy did not recover, so underwent secondary scaphotrapezio-trapezoidal fusion. In conclusion, we found that various degrees of scapholunate interosseous ligament tear and scaphotrapezio-trapezoidal joint osteoarthritis were the main causes of radial-sided wrist pain with inconclusive X-ray and simple MRI findings.

Role of the Periosteal Flap in Chondrocyte Transplantation: An Experimental Study in Rabbits

To determine the role of the periosteal flap in chondrocyte transplantation for the treatment of articular cartilage defects, a cartilage defect was created on the patellar groove of the rabbit knee. The defect was filled with chondrocytes cultured in collagen gel, and was covered with a periosteal flap the cambial layer of which was facing the patella (P group), or facing down against the bone marrow (M group). The same defect was covered with a periosteal flap that was frozen and thawed three times (F group), and an artificial collagen film (C group). At 3 and 6 months, the defects were filled with reparative tissues that showed a smooth surface and resembled hyaline cartilage in the P, M, and F groups. There were no significant differences between the reparative tissues in the three groups histologically, immunohistochemically, biochemically, and biomechanically, although the collagen film fell down into the defect and the reparative tissue had a fibrous tissue-like appearance. These results showed that the periosteal flap does not have a beneficial humoral or cellular effect on the formation of reparative tissue, suggesting that the periosteal flap might act as a mechanical barrier to prevent leakage of grafted chondrocytes.

Mechanical properties of newly developed loop ligament for connection between the EndoButton and hamstring tendons: comparison with Ethibond sutures and Endobutton tape

A new artificial loop ligament (LL) without mechanical weak points, such as a knot, has been developed to connect the EndoButton and hamstring tendons for anterior or posterior cruciate ligament (CL) reconstruction. This study assessed the mechanical properties of the LL and sutures (No. 5 Ethibond thread, EndoButton tape) and those of the different CL constructs with these materials and fixation devices commonly used in CL reconstruction. The LL had a significantly higher ultimate tensile load (UTL) and stiffness value (p < 0.001) than No. 5 Ethibond thread or EndoButton tape in static and fatigue tests (50--500 N, 1.08 million cycles). The LL-tendons-Leeds-Keio artificial ligament-staple construct complex also had significantly higher UTL and stiffness value than the Ethibond loops or EndoButton tape loop-tendons-Ethibond sutures-postscrew-fixed construct complex. Furthermore, the LL construct complex elongated the least after cyclic loading (50--150 N, 90,000 cycles). These findings suggested that using the LL construct complex might avoid a bungee cord effect and elongation before biological healing between the construct and bony socket. The LL construct complex could be a safe substitute for use during the postoperative period.

Effects of cell density on proliferation and matrix synthesis of chondrocytes embedded in atelocollagen gel

The effects of cell density on the proliferation and chondroitin sulfate synthesis of chondrocytes embedded in Atelocollagen gel were examined. Chondrocytes of 21 10-week-old Japanese white rabbits isolated by collagenase digestion were embedded in Atelocollagen gel and cultured in Dulbecco's modified Eagles medium at cell densities of 2 x 105 cells/ml (105 group), 2 x 106 cells/ml (106 group), and 2 x 107 cells/ml (107 group) for 4 weeks. Chondrocytes in the 105 group gradually proliferated more than the other two groups. In contrast, most chondrocytes in the 107 group showed increased capability to produce chondroitin 6-sulfate. Cartilage-like tissue was produced from high-density cultures (107 cells/ml), although a decrease in cell number was seen. Even in three-dimensional cultures, the proliferation and chondroitin sulfate synthesis of chondrocytes were influenced by the cell density. These results are informative for the clinical application of chondrocyte transplantation in three-dimensional cultures for cartilage repair.

Treatment of growth plate injury with autogenous chondrocytes: a study in rabbits

We designed this study to investigate transplantation of autogenous chondrocytes cultured in atelocollagen gel to treat the injured growth plate. An experimental model of growth arrest was made by resecting the medial two thirds of the left proximal tibial physis in 8-10-week-old Japanese white rabbits. Autogenous chondrocytes, which had been harvested from cartilage of the knee joints, embedded in atelocollagen gel, and cultured for a week, were transplanted into the defect in the growth plate. In two other experimental groups, we transplanted autogenous fat tissue into the same defects, or left them empty. Histological and radiographic examinations were done before and after transplantation at various times up to 52 weeks postoperatively. The histological study showed that grafted chondrocytes synthesized extracellular matrix and prevented early ossification and closure of the growth plate, which occurred in the Fat and Defect groups. Angular deformity and length discrepancy in the transplanted group were less than in the control group. Our findings suggest that transplantation of autogenous chondrocytes, cultured in atelocollagen gel, may improve treatment of the injured growth plate.

Effects of low-intensity pulsed ultrasound on proliferation and chondroitin sulfate synthesis of cultured chondrocytes embedded in Atelocollagen gel

The effects of low-intensity pulsed ultrasound (US) on the proliferation and chondroitin sulfate synthesis of cultured chondrocytes embedded in Atelocollagen gel in vitro were examined. Articular cartilage was harvested from the hip, knee, and shoulder joints of 10-week-old Japanese white rabbits. Chondrocytes isolated by collagenase digestion were embedded in type I collagen gel, Atelocollagen gel, and were cultured in Dulbecco's modified eagle's medium for 3 weeks. The US apparatus, SAFHS, was used to deliver an ultrasound signal with spatial and temporal average intensities of 30 mW/cm(2) (US group). The frequency was 1.5 MHz with a 200-microsecond tone burst repeated at 1.0 kHz. US treatments were administered for 20 min per day under culture dishes, with the medium replaced twice a week. Another group of cells was exposed to sham ultrasound as a control. Cell number, histological findings, synthesis of isomers of chondroitin sulfate, and stiffness of the chondrocyte-collagen gel composites were analyzed. US exposure promoted synthesis of chondroitin sulfate, especially chondroitin 6-sulfate, although it did not significantly enhance cell number and stiffness. In this three-dimensional culture model, these results suggest that US exposure may be clinically useful in improving the quality of chondrocyte-Atelocollagen implants for transplantation into articular cartilage defects.

Loss of syndecan-1 and increased expression of heparanase in invasive esophageal carcinomas

Heparan sulfate proteoglycans play important biological roles in cell-cell and cell-matrix adhesion, and are closely associated with growth factor actions. Loss of syndecan-1, a cell surface-bound heparan sulfate proteoglycan, has been reported for advanced head and neck carcinomas, and expression of endoglycosidic heparanase, which cleaves heparan sulfate glycosaminoglycans (HS-GAGs), is associated with invasion and metastatic potential of malignant tumors. Paraffin sections of 103 primary esophageal squamous cell carcinomas were immunohistochemically examined for the expression of syndecan-1 core protein, HS-GAGs and heparanase protein, and the results were compared with various clinicopathological parameters, such as invasion depth. For 16 cases, fresh tumor samples were quantitatively analyzed for heparanase and syndecan-1 mRNA expression by real-time RT-PCR in addition to the immunohistochemical studies. Syndecan-1 core protein and HS-GAGs expression was significantly decreased in pT2 and pT3 cases compared with their pTis and pT1 counterparts. Decreased expression of core protein and HS-GAGs was correlated with the incidence of lymphatic invasion, and venous involvement. Furthermore, decreased expression of HS-GAGs was correlated positively with the incidence of nodal metastasis and distant organ metastasis, and negatively with the grade of tumor cell differentiation. The percentage of cytoplasmic heparanase protein-positive cases increased significantly in pT2 and pT3 cases compared to that in pTis and pT1 cases, and this was associated with lymphatic invasion, and venous and lymph nodal involvement. The level of heparanase mRNA was inversely correlated with the degree of HS-GAGs expression rather than core protein. In conclusion, loss of syndecan-1 and heparanase overexpression in esophageal squamous cell carcinomas are closely associated with malignant potential. Regarding the mechanism of loss of HS-GAGs, heparanase upregulation appears to play an important role.

Perinuclear and cytoplasmic distribution of desmoglein in esophageal squamous cell carcinomas

The desmosomal glycoproteins desmoglein (Dsg) and desmocollin (Dsc) are members of the cadherin family of cell adhesion molecules. They play an important role in epithelial adhesion. To observe the distribution pattern of Dsg in esophageal squamous cell carcinomas (SCC), immunohistochemical and immunoelectron microscopic analyses were performed. Immunohistochemically, normal esophageal squamous cells strongly expressed Dsg at the cell-cell boundaries, while moderately differentiated esophageal SCC cells showed a perinuclear distribution in addition to the cell boundary staining. At the ultrastructural level, the reaction product was concentrated at the desmosomes in the cell membrane region of normal epithelial cells, but was reduced at the membrane and found throughout the cytoplasm as well as in the surrounding outer nuclear envelope in SCC cells. These results demonstrate an aberrant distribution of Dsg in SCC cells. This may have important consequences for invasion and metastasis, as it may indicate loosened intercellular adhesion.

Proprioceptive improvement in knees with anterior cruciate ligament reconstruction

The correlation between the prospective course of proprioceptive improvement and knee stability after anterior cruciate ligament reconstruction was investigated in 38 patients. Proprioception, on the basis of the patient's capacity to reposition the limb accurately, was evaluated at 3-month intervals for 24 months after hamstring graft anterior cruciate ligament surgery. Knee stability was evaluated concurrently with a KT-2000 knee arthrometer. Thirty patients experienced improvement in postoperative position sense in at least one of the examinations, although eight patients had no improvement at any time. Of the 30 patients who had improvement, 28 maintained improved position sense from 18 months to the final followup. Thirty patients maintained significantly better knee stability for a postoperative period of at least 24 months. These results indicated that a minimum of 18 months after anterior cruciate ligament reconstruction may be needed for complete restoration of the proprioceptive function in knees, although the mean position sense in all patients gradually improved from 9 months. Improvement in postoperative knee stability may have facilitated recovery of proprioception.

Human chondrocyte proliferation and matrix synthesis cultured in Atelocollagen gel

To evaluate the potential of Atelocollagen gel as a carrier for chondrocyte transplantation, histological and biochemical characteristics of the chondrocytes in gel culture were compared with those in conventional monolayer cultures. Articular chondrocytes from 20 patients were isolated by enzyme digestion, embedded in Atelocollagen gel, and cultured for up to 4 weeks. The effects on proliferation, morphological changes, and synthesis of proteoglycans were analyzed by cell counts, light and electron microscopy, and measurement of isomers of chondroitin sulfates. Chondrocytes embedded in the Atelocollagen gel gradually proliferated and produced chondroitin 6-sulfate, maintaining the chondrocyte phenotype for up to 4 weeks. In contrast, although monolayer chondrocytes increased in number, most could be characterized as being fibroblast-like cells with a reduced capability of producing chondroitin 6-sulfate. The results suggest that Atelocollagen gel permitted a gradual proliferation and matrix synthesis of chondrocytes and maintaining its phenotype. Atelocollagen gel represents an important carrier for the clinical application of cultured chondrocyte transplantation for repair of cartilage defects.

Repair of articular cartilage defects with cultured chondrocytes in Atelocollagen gel. Comparison with cultured chondrocytes in suspension

We attempted to repair full-thickness articular cartilage defects in rabbit knee joints with allogeneic cultured chondrocytes embedded in Atelocollagen gel. An articular cartilage defect was created on the patellar groove of the femur. The defect was filled with chondrocytes cultured in the collagen gel and covered with periosteal flap (G group). In three other experimental groups, the same defects were transplanted with chondrocytes in monolayer culture with periosteal flap (M group), periosteal graft only (P group), or left empty (E group). At 4, 12, and 24 weeks after operation, the reparative tissue was analyzed macroscopically and histologically. At 4 weeks after operation, the surfaces of the reparative tissue were smooth, and the defects were filled with reparative tissues that resembled hyaline cartilage in all four groups. However, the reparative tissues degenerated gradually with time in the M, P, and E groups. In contrast, in the G group, the reparative tissue retained its thickness, and there was a steady integration of the grafted tissue into the adjacent normal cartilage at 24 weeks after operation. The results suggest that transplantation of allogeneic chondrocytes cultured in Atelocollagen gel is effective in repairing an articular cartilage defect.

Successful restoration of the trapezius muscle using pedicle latissimus dorsi. A case report

Reconstruction of the trapezius muscle using a pedicle latissimus dorsi flap was performed in a 27-year-old man with a large synovial sarcoma in his shoulder girdle. Size and location of the tumor required combined resection of surrounding muscles, including the trapezius, levator scapulae, and rhomboid major and minor. Thus, an extensive defect of the suspending muscles of the scapula was created after accomplishing an adequate resection of the tumor. The flap was performed to restore the trapezius functionally because there were no adjacent muscles available. The transferred muscle compensated for loss of the trapezius, thereby recovering excellent shoulder function. Although an opportunity of its application is thought to occur infrequently, the pedicle latissimus dorsi can activate scapular motion successfully in the absence of the levator scapulae. The technique may be extended to salvage failed conventional reconstruction after spinal accessory nerve palsy.

Identification and characterization of a putative sevenless homologue in the malaria vector Anopheles gambiae

Tyrosine kinase sequences were identified and characterized in Anopheles gambiae, the major vector of malaria in subsaharan Africa. One of these sequences has the characteristics expected for a homologue of the Drosophila sevenless gene, which is necessary for R7 photoreceptor cell fate determination in the developing compound eye. The putative Anopheles sevenless gene homologue is located in a telomeric region of the X chromosome and is expressed in the head of late larval and pupal stage mosquitoes. Identification of the Anopheles homologue of the sevenless gene is a first step towards the development of a dominant phenotypic marker that could be used for detecting transformed Anopheles mosquitoes in a wide variety of genetic backgrounds and, as such, could be used in the development of transgenic mosquitoes for the control of parasite transmission. Preliminary evidence for sevenless sequences were also found in DNA from blackfly, Mediterranean fruit fly and the honeybee.

Successful nerve regeneration and persistence of donor cells after a limited course of immunosuppression in rat peripheral nerve allografts

BACKGROUND

The origin of Schwann cells and effect of a limited course of immunosuppression using cyclosporine (CsA) were examined in rat peripheral nerve allotransplants.

METHODS

Phenotypes of Schwann cells in groups without, with continuing, and with limited (12 weeks) CsA treatment were examined immunohistochemically in allogeneically and syngeneically transplanted animals from 4 to 36 weeks after transplantation.

RESULTS

In the group receiving no CsA, little nerve regeneration was obtained; donor Schwann cells were rejected and replaced by recipient cells. In continuing and limited-course CsA groups, successful nerve regeneration was achieved at postoperative week 36, as was also observed in the syngeneic group. Schwann cells in the continuing CsA group remained donor-derived. In the limited-course CsA group, graft rejection and loss of function occurred after the withdrawal of CsA, and donor Schwann cells were replaced by recipient cells in the part of the graft where rejection had been complete. However, many donor Schwann cells remained at week 36, when the rejection response subsided.

CONCLUSION

Possible clinical use of a limited course of immunosuppression was supported by this demonstration of long term persistence of donor Schwann cells.

Molecular cloning of the chick Nau gene and analysis of its expression patterns during neurogenesis

We have previously identified a novel gene, Nau (Neuron-specific gene, which has a number of AU-rich RNA instability motifs), from a quail spinal cord cDNA library. Nau expression was observed mainly in post-mitotic neuroblasts, especially in the stage of axonogenesis. In this study, we cloned its chick orthologue (cNau, 5069 bp), which encodes 369 amino acid residues. cNau's open reading frame has three highly conserved regions with rat STOP (stable tubule-only polypeptide). cNau may be an orthologue of STOP gene considering its uniqueness in zoo blot analysis and its sequence similarity. Both the genetic structure and temporo-spatial expression patterns indicate that the cNau gene may be related to axonogenesis. In the hindbrain, cNau mRNA was accumulated in rhombomere boundary regions and in the rhombomere 2, 4 and 6. These observations suggest a specific role of cNau in the hindbrain or the difference in development between the hindbrain and spinal cord.

Ectopic expression of lunatic Fringe leads to downregulation of Serrate-1 in the developing chick neural tube; analysis using in ovo electroporation transfection technique

Lunatic Fringe (l-Fng) is one of the vertebrate homologues of Drosophila Fringe, which interacts with the Notch signal pathway and regulates activation of the Notch ligands, Delta and Serrate. To elucidate the roles of l-Fng in vertebrate neurogenesis, we transfected chick l-Fng (C-l-Fng) to chick neural tube using the in ovo electroporation technique and examined the subsequent changes in expression of Notch-related genes. We observed downregulation of C-Serrate-1 by ectopic C-l-Fng expression which implied that C-l-Fng acts on the vertebrate Notch pathway to regulate the expression of its ligand.

Identification of a chick homologue of Fringe and C-Fringe 1: involvement in the neurogenesis and the somitogenesis

In Drosophila, Serrate plays an important role to the wing margin formation. A putative secretory protein, Fringe, is indispensable for the wing margin formation inducing Serrate and other genes. Recently, Xenopus homologues of Fringe were identified and one of them, lunatic Fringe (X-lFng), was demonstrated to be involved in mesoderm induction. We have identified two chick Fringe homologous genes by reverse transcription-polymerase chain reaction and cDNA library screening. One of them, C-Fringe 1, showed sequence similarity to X-lFng. In situ hybridization study of C-Fringe 1 has demonstrated its expression in the developing nervous system and in the presomitic mesoderm. The hindbrain and spinal cord showed the distinct stripe pattern expression which was complementary to that of C-Serrate, indicating the correlation between them in vertebrate.

Nerve regeneration and origin of Schwann cells in peripheral nerve allografts in immunologically pretreated rats

For peripheral nerve allografts, the conditions for successful nerve regeneration and the possibility of transplanting Schwann cells were examined using a model of pretreated rats. Incomplete immunosuppression was achieved in recipient rats with donor red blood cell infusions given before allogeneic nerve grafting (RBC group). The origin of Schwann cells in the grafts was assessed by immunohistochemical staining from 1 week to 12 weeks after transplantation. In the RBC group, the replacement of donor Schwann cells by recipient cells was detected at 3-8 weeks, with the graft being filled with many of these cells at all times, and successful nerve regeneration was seen after 12 weeks on morphometric and electrophysiologic evaluations. In peripheral nerve allografts, pretreatment with donor-specific blood transfusion did not induce significant immunosuppression compared with allotransplantations of some tissues and organs. Clinically, if the state of immunosuppression can be controlled by RBC transfusion, it is possible that donor tissues may be replaced by recipient tissues and that nerves will regenerate successfully.

Elevation of transforming growth factor beta 1 mRNA level in ES-D3 mouse embryonic stem cells cocultured with Balb/c3T3 A31 fibroblasts

Embryonic stem (ES) cells are a pluripotent cell line derived from the inner cell mass of the mouse blastocyst. The mRNA levels of several growth-related genes were examined in ES cells by Northern blot analysis under several different growth conditions. In a coculture of ES cells with the mouse fibroblast cell line, Balb/c3T3 A31, the expression level of transforming growth factor beta 1 (TGF-beta 1) mRNA was elevated for 1 to 3 days. In a coculture of ES cells with primary embryonic fibroblasts, only slight accumulation of TGF-beta 1 mRNA was observed for 6 to 24 h and soon attenuated. In situ hybridization analysis revealed that TGF-beta 1 transcripts accumulated first in the masses of ES cells and subsequently in Balb/c3T3 A31 cells adjacent to ES cells' masses. The ability of ES cells to induce TGF-beta 1 in Balb/c3T3 A31 cells was not mediated by soluble factors and was lost upon differentiation. ES cells on primary embryonic fibroblasts grew in undifferentiated form, but those on Balb/c3T3 A31 cells stopped growing and formed embryoid cystic bodies. We suggest that TGF-beta 1 mRNA induction in a coculture is triggered by an interaction between differentiating ES cells and Balb/c3T3 A31, and that this activity is limited to undifferentiated ES cells.