Hematopoiesis occurs in close association with a complex network of cells loosely termed the hematopoietic microenvironment. Analysis of the mechanisms of microenvironmental regulation of hematopoiesis has been hindered by the complexity of the microenvironment as well as the heterogeneity of hematopoietic stem cells and early progenitor cells. We have established immortalized primate bone marrow-derived stromal cell lines to facilitate analysis of the interactions of hematopoietic cells with the microenvironment in a large animal species. One such line, PU-34, was found to produce a variety of growth factors, including an activity that stimulates the proliferation of an interleukin 6-dependent murine plasmacytoma cell line. A cDNA encoding the plasmacytoma stimulatory activity was isolated through functional expression cloning in mammalian cells. The nucleotide sequence contained a single long reading frame of 597 nucleotides encoding a predicted 199-amino acid polypeptide. The amino acid sequence of this cytokine, designated interleukin 11 (IL-11), did not display significant similarity with any other sequence in the GenBank data base. Preliminary biological characterization indicates that in addition to stimulating plasmacytoma proliferation, IL-11 stimulates the T-cell-dependent development of immunoglobulin-producing B cells and synergizes with IL-3 in supporting murine megakaryocyte colony formation. These properties implicate IL-11 as an additional multifunctional regulator in the hematopoietic microenvironment.

The maintenance and differentiation of hematopoietic stem cells is influenced by cells making up the hematopoietic microenvironment (HM), including bone marrow-derived stromal cells. We and several other investigators have recently demonstrated the molecular basis of abnormal HM observed in the steel mutant mouse and cloned the normal cDNA products of this gene (termed SCF, KL, or MCF). In this report, we focus on the human counterpart of the mouse Steel (Sl) gene. Alternative splicing of the human SCF pre-mRNA transcript results in secreted and membrane-bound forms of the protein. To investigate the role of these two forms of human SCF, we targeted an immortalized stromal cell line derived from fetal murine homozygous (Sl/Sl) SCF-deficient embryos for gene transfer of various human cDNAs encoding SCF. We report that stable stromal cell transfectants can differentially process the two forms of human SCF protein product. We also demonstrate that both soluble SCF and membrane-bound SCF are active in increasing the number of human progenitor cells in the context of stromal cell cultures, although in a qualitatively different manner. Hence, the membrane-bound form of SCF may play an important role in the cell-cell interactions observed between stromal and hematopoietic cells both in vitro and in vivo.

Metabolic inhibitors based on rare bacterial monosaccharide scaffolds interfere with bacterial glycan biosynthesis in a bacteria-selective manner.

The gene coding for 18S small subunit ribosomal RNA (ssu rRNA) was sequenced in seven free-living, marine species of the sessiline peritrich genus Zoothamnium. These were Zoothamnium niveum, Zoothamnium alternans, Zoothamnium pelagicum, and four unidentified species. The ssu rRNA gene also was sequenced in Vorticella convallaria, Vorticella microstoma, and in an unidentified, freshwater species of Vorticella. Phylogenetic trees were constructed using these new sequences to test a previously published phylogenetic association between Zoothamnium arbuscula, currently in the family Zoothamniidae, and peritrichs in the family Vorticellidae. Trees constructed by means of neighbor-joining, maximum parsimony, maximum likelihood, and Bayesian inference methods all had similar topologies. The seven new sequences of Zoothamnium species grouped into three well-supported clades, each of which contained a diversity of morphological types. The three clades formed a poorly supported, larger clade that was deeply divergent from Z. arbuscula, which remained more closely associated with vorticellid peritrichs. It is apparent that Zoothamnium is a richly diverse genus and that a much more intensive investigation, involving both morphological and molecular data and a wider selection of species, will be necessary to resolve its phylogeny. A greater amount of molecular diversity than is predicted by morphological data exists within all major clades of sessiline peritrichs that have been included in molecular phylogenies, indicating that characteristics of stalk and peristomial structure traditionally used to differentiate taxa at the generic level and above may not be uniformly reliable.

The gene encoding 18S small subunit ribosomal RNA (ssu rRNA) was sequenced in the sessiline peritrichs Opisthonecta minima and Opisthonecta matiensis, whose free-swimming, paedomorphic trophonts resemble telotrochs. Using these new sequences, phylogenetic trees were constructed with four different methods to test a previously published association between Opisthonecta henneguyi and members of the families Vorticellidae and Astylozoidae. All trees had similar topologies, with O. minima, O. henneguyi, Vorticella microstoma, and Astylozoon enriquesi forming a well-supported, certainly monophyletic clade. On the basis of genetic evidence, genera of the families Opisthonectidae and Astylozoidae are assigned to the family Vorticellidae, which already includes some species with free-swimming morphotypes. The ssu rRNA sequence of O. matiensis places it in the family Epistylididae; its taxonomic revision will be left to another group of authors. A close association of Ophrydium versatile with members of the family Vorticellidae was confirmed, casting doubt on the validity of the family Ophrydiidae. Epistylis galea, Campanella umbellaria, and Opercularia microdiscum are confirmed as comprising an extremely distinct, monophyletic, but morphologically heterogeneous clade that is basal to other clades of sessiline peritrichs.