Labidocera aestiva and L. scotti in Tamiahua Lagoon,Veracruz, Mexico

Labidocera aestiva and L. scotti were found in the Tamiahua Lagoon, Veracruz, Mexico. Fleminger (1957) found that the populations of these species may overlap geographically, although L. aestiva has affinity to the Carolinian province and L. scotti to the Caribbean province. This study describes the seasonal behavior and succession of this species in the Tamiahua Lagoon, a brackish water system with a high marine influence. A qualitative and quantitative analysis of samples was made in March, July, and September 1985 and January 1986. L. aestiva was found in temperatures below 26 °C in a wide salinity range. At temperatures above 26 °C and up to 32 °C, L. aestiva was present also with euryhaline character. In the Tamiahua Lagoon these two species did not overlap during this study. Both species are considered temporary inhabitants of this estuarine system in the Western Gulf of Mexico.     

Fibronectin promotes differentiation of neural crest progenitors endowed with smooth muscle cell potential

The neural crest (NC) is a model system used to investigate multipotency during vertebrate development. Environmental factors control NC cell fate decisions. Despite the well-known influence of extracellular matrix molecules in NC cell migration, the issue of whether they also influence NC cell differentiation has not been addressed at the single cell level. By analyzing mass and clonal cultures of mouse cephalic and quail trunk NC cells, we show for the first time that fibronectin (FN) promotes differentiation into the smooth muscle cell phenotype without affecting differentiation into glia, neurons, and melanocytes. Time course analysis indicated that the FN-induced effect was not related to massive cell death or proliferation of smooth muscle cells. Finally, by comparing clonal cultures of quail trunk NC cells grown on FN and collagen type IV (CLIV), we found that FN strongly increased both NC cell survival and the proportion of unipotent and oligopotent NC progenitors endowed with smooth muscle potential. In contrast, melanocytic progenitors were prominent in clonogenic NC cells grown on CLIV. Taken together, these results show that FN promotes NC cell differentiation along the smooth muscle lineage, and therefore plays an important role in fate decisions of NC progenitor cells.     

Mouse placenta is a major hematopoietic organ

Placenta and yolk sac from 8- to 17-day-old (E8-E17) mouse embryos/fetuses were investigated for the presence of in vitro clonogenic progenitors. At E8-E9, the embryonic body from the umbilicus caudalwards was also analysed. Fetal liver was analysed beginning on E10. At E8, between five and nine somite pairs (sp), placenta, yolk sac and embryonic body yielded no progenitors. The first progenitors appeared at E8.5 at the stage of 15 sp in the yolk sac, 18 sp in the embryonic body, 20 sp in the placenta and only at E12 in the fetal liver (absent at E10, at E11 not determined). Progenitors with a high proliferation potential that could be replated for two months, as well as the whole range of myeloid progenitors, were found at all stages in all organs. However, the earliest of these progenitors (these yielding large, multilineage colonies) were 2-4 times more frequent in the placenta than in the yolk sac or fetal liver. In the fetal liver, late progenitors were more frequent and the cellularity increased steeply with developmental age. Thus, the fetal liver, which is a recognized site for amplification and commitment, has a very different hematopoietic developmental profile from placenta or yolk sac. Placentas were obtained from GFP transgenic embryos in which only the embryonic contribution expressed the transgene. 80% of the colonies derived from these placental cells were GFP+, and so originated from the fetal component of the placenta. These data point to the placenta as a major hematopoietic organ that is active during most of pregnancy.     

Thyroid Hormone Mediates Syndecan Expression in Rat Neonatal Cerebellum

Thyroid hormone (T₃) plays an essential role in the central nervous system development. Astrocytes mediate many of the T₃ effects in the growth and differentiation of cerebellum. In culture, T₃ induces cerebellar astrocytes to secrete growth factors, mainly FGF₂, and alters the expression and organization of the extracellular matrix (ECM) proteins, laminin, and fibronectin. In addition, T₃-treated astrocytes promote neuronal differentiation. In this study, we have investigated whether other ECM molecules, such as syndecans, are involved in T₃ action. Thus, we analyzed the expression of syndecans (1–4) by RT-PCR in astrocyte cultures from cerebellum, cortex, and hippocampus of newborn rats. Our results showed that syndecans (1–4) are expressed in astrocytes of cerebellum and cortex, whereas in hippocampus only syndecans 2 and 4 were detected. Semi-quantitative RT-PCR analysis revealed the reduced expression of syndecans 1, 2, and 4, and increased expression of syndecan 3 in hypothyroid cerebellum, when compared to the euthyroid tissue. Furthermore, we observed a reduced expression of syndecans 2 and 3 in T₃-treated cerebellar astrocytes, when compared to control cultures. This balance of proteoglycans may be involved in T₃ action mediated by FGF₂ signaling, possibly affecting the formation of the trimeric signaling receptor complex composed by syndecan/FGF/FGF-receptor (FGFR), which is essential for FGFR dimerization, activation, and subsequent cell signaling.     

Isolation and replication of rabies virus in C6 rat glioma cells (clone CCL-107).

The susceptibility of the C6 rat glioma cell line (ATCC; CCL-107) to rabies virus was characterized. The kinetics of infection performed with a fixed and a wild strain (from an infected cow) of rabies virus was monitored by direct immunofluorescence. Fluorescent cytoplasmic bodies were readily observed by UV microscopy from 24 hours post-infection (hpi) onwards. The ability of C6 to produce rabies infective virion particles was confirmed by determining the viral titres present in the supernatants of infected cultures, by both BHK-21 cell infection and mice inoculation. C6 cells produced similar viral titres to those produced by BHK-21 for both strains used. In addition, the yield of rabies glycoprotein was assessed by ELISA. In general, BHK-21 and C6 cells infected either by PV or with the wild rabies strain produced similar amounts of rabies glycoprotein. At 96 hpi, however, when the glycoprotein production peaked, BHK-21 infected with the wild strain produced significantly higher amounts of glycoprotein than C6. Subsequently, the optimal conditions for isolation of wild rabies virus strains from C6 cells were established and these proved to be as sensitive as NA cells in detecting 10 wild rabies samples. Due to the high sensitivity exhibited, C6 rat glioma cells present a new and useful system for rabies virus investigation.     

Glycosaminoglycans modulate C6 glioma cell adhesion to extracellular matrix components and alter cell proliferation and cell migration

Background  

Adhesion to extracellular matrix (ECM) components has been implicated in the proliferative and invasive properties of tumor cells. We investigated the ability of C6 glioma cells to attach to ECM components in vitro and described the regulatory role of glycosaminoglycans (GAGs) on their adhesion to the substrate, proliferation and migration.     

Thyroid hormone induces cerebellar astrocytes and C6 glioma cells to secrete mitogenic growth factors

In this study, the effect of thyroid hormone (triiodothyronine, T(3)) on the secretion of mitogenic growth factors in astrocytes and C6 glioma cells was examined. The proliferating activity of T(3) could be due, at least in part, to the astrocyte secretion of acidic and basic fibroblast growth factor (aFGF and bFGF), tumor necrosis factor-beta, and transforming growth factor-beta. In contrast, the conditioned medium (CM) of T(3)-treated C6 cells was mitogenic to this cell line only after hyaluronidase digestion, suggesting the impairment of growth factor mitogenic activity by hyaluronic acid. Furthermore, the presence of bFGF was significantly greater in the CM of both T(3)-treated astrocytes and T(3)-treated C6 cells than in the corresponding control CM. These data show that T(3) induces cerebellar astrocytes to secrete mitogenic growth factors, predominantly bFGF, that could influence astrocyte and neuronal proliferation via autocrine and paracrine pathways.     

Epidermal Growth Factor (EGF) Promotes the In Vitro Differentiation of Neural Crest Cells to Neurons and Melanocytes

Proliferation of neural crest (NC) stem cells and their subsequent differentiation into different neural cell types are key early events in the development of the peripheral nervous system. Soluble growth factors present at the sites where NC cells migrate are critical to the development of NC derivatives in each part of the body. In the present study, we further investigate the effect of microenvironmental factors on quail trunk NC development. We show for the first time that EGF induces differentiation of NC to the neuronal and melanocytic phenotypes, while fibroblast growth factor 2 (FGF2) promotes NC differentiation to Schwann cells. In the presence of both EGF and FGF2, the neuronal differentiation predominates. Our results suggest that FGF2 stimulates gliogenesis, while EGF promotes melanogenesis and neurogenesis. The combination of both growth factors stimulates neurogenesis. These findings suggest that these two growth factors may play an important role in the fate decision of NC progenitors and in the development of the peripheral nervous system.