Multipotential stem cells have been isolated from the developing and adult CNS. Similar identified factors control the differentiation of these cells. A striking example is the instructive action of CNTF/LIF activating the JAK/STAT pathway to induce astrocytic differentiation in both fetal and adult CNS stem cells. Here we show that E12 cortical precursors express functional LIF receptors but do not exhibit this differentiation response to CNTF/LIF either in explant or in dissociated cell culture. The lack of response to LIF-induced astrocytic differentiation is maintained in cocultures with LIF responsive cells derived from E15 cortex. This suggests cell intrinsic differences between early and late stage precursors in the interpretation of LIF-mediated signaling; however, the early nestin-positive precursor population differentiates into both neurons and neural crest derivatives. These data define differences between CNS stem cells from different stages of cortical development. J. Neurosci. Res. 59:301-311, 2000. Published 2000 Wiley-Liss, Inc.

These mice have phenotypic features consistent with the commonly observed clinical features of RTH and could be used as a model system to better understand the action of mutant TR beta 1 in a physiological context, which could lead to better treatment for this disease.

Murine leukemia virus (MLV)-derived envelope proteins containing alterations in or adjacent to the highly conserved PHQ motif present at the N terminus of the envelope surface subunit (SU) are incorporated into vector particles but are not infectious due to a postbinding block to viral entry. These mutants can be rendered infectious by the addition of soluble receptor-binding domain (RBD) proteins in the culture medium. The RBD proteins that rescue the infectivity of these defective MLV vectors can be derived from the same MLV or from other MLVs that use distinct receptors to mediate entry. We have now constructed functional immunologically reactive gibbon ape leukemia virus (GALV) envelope proteins, tagged with a feline leukemia virus (FeLV)-derived epitope tag, which are efficiently incorporated into infectious particles. Tagged GALV envelope proteins bind specifically to cells expressing the phosphate transporter protein Pit1, demonstrating for the first time that Pit1 is the binding receptor for GALV and not a coreceptor or another type of GALV entry factor. We have also determined that GALV particles bearing SU proteins with an insertion C-terminal to the PHQ motif (GALV I Virus receptors are the components of cell membranes that allow viral attachment, the first step in infection. It has traditionally been thought that viruses infect and replicate in some cell types, but not others, because of the distribution of specific virus receptors on different cells. Now it is well known that although the presence of specific receptors is critical for viral entry, coreceptors and postentry factors are also important in defining the virus's host range. Some cells express the appropriate receptors but are nevertheless resistant to infection by a specific virus. In many cases, discrepancies between virus receptor distribution and virus host range can be accounted for by cell-specific expression of coreceptors or other ancillary factors required for membrane fusion and internalization of a virus after its initial attachment to its primary receptor. For example, the human CD4 molecule acts as a primary receptor for human immunodeficiency virus type 1 (HIV-1) infection when expressed in human cells but not when expressed in murine cells. When human CD4 is expressed in murine cells, it supports HIV-1 binding but not infection; infection can proceed if such cells express the appropriate coreceptor (reviewed in reference 34). Similarly, Pit1 acts as a primary receptor for feline leukemia virus type T (FeLV-T); however, infection by FeLV-T requires the presence of the FeLIX cofactor (1).In addition to FeLV-T, the phosphate transporter Pit1 has been proposed to serve as the receptor for gibbon ape leukemia virus (GALV) (31), feline leukemia virus subgroup B (FeLV-B) (40), and murine leukemia virus (MLV) 10A1 (30, 43). GALV infects a wide variety of cell types (21) derived from diverse species (20). Because of its broad host range, GALV-based retroviral vectors have been developed for use in both in vivo and ex vivo gene trans...

The thyroid hormone nuclear receptors (TRs) are ligand-dependent transcription factors. To understand the molecular basis of ligand-dependent transactivation, we studied the structure of their carboxy-terminal activation domain. We analyzed the structures of the peptides derived from the C-terminal sequences of human TR subtypes beta 1 (h-TR beta 1) and alpha 1 (h-TR alpha 1) and a human TR mutant, PV, by circular dichroism (CD). Mutant PV has a C-terminal frameshift mutation and does not bind to the thyroid hormone, 3,3',5-triiodo-L-thyronine (T3). Analyses of the secondary structures of the peptides by CD indicate that five amino acids, EVFED, are part of an amphipathic alpha-helix which is required to maintain the structural integrity of the hormone binding domain. A monoclonal antibody, C4 (mAb C4), which recognizes both h-TR beta 1 and h-TR alpha 1 was developed. Using a series of truncated mutants and synthetic peptides, we mapped the epitope of mAb C4 to the conserved C-terminal amino acids, EVFED. Analysis of the binding data indicates that binding of T3 to either h-TR beta 1 or h-TR alpha 1 was competitively inhibited by mAb C4. Deletion of C-terminal amino acids including EVFED led to a total loss of T3 binding activity. Thus, part of the T3 binding site is located in this five amino acid segment. T3 may transduce its hormonal signal to the transcriptional machinery via interaction with EVFED at the C-terminus of TRs.