Targeted deletion of the mouse POU domain gene Brn-3a causes selective loss of neurons in the brainstem and trigeminal ganglion, uncoordinated limb movement, and impaired suckling.

The Brn-3 subfamily of POU domain genes are expressed in sensory neurons and in select brainstem nuclei. Earlier work has shown that targeted deletion of the Brn-3b and Brn-3c genes produce, respectively, defects in the retina and in the inner ear. We show herein that targeted deletion of the Brn-3a gene results in defective suckling and in uncoordinated limb and trunk movements, leading to early postnatal death. Brn-3a (-/-) mice show a loss of neurons in the trigeminal ganglia, the medial habenula, the red nucleus, and the caudal region of the inferior olivary nucleus but not in the retina and dorsal root ganglia. In the trigeminal and dorsal root ganglia, but not in the retina, there is a marked decrease in the frequency of neurons expressing Brn-3b and Brn-3c, suggesting that Brn-3a positively regulates Brn-3b and Brn-3c expression in somatosensory neurons. Thus, Brn-3a exerts its major developmental effects in somatosensory neurons and in brainstem nuclei involved in motor control. The pheno-types of Brn-3a, Brn-3b, and Brn-3c mutant mice indicate that individual Brn-3 genes have evolved to control development in the auditory, visual, or somatosensory systems and that despite differences between these systems in transduction mechanisms, sensory organ structures, and central information processing, there may be fundamental homologies in the genetic regulatory events that control their development.

Long-term modifications of synaptic efficacy in the human inferior and middle temporal cortex.

The primate temporal cortex has been demonstrated to play an important role in visual memory and pattern recognition. It is of particular interest to investigate whether activity-dependent modification of synaptic efficacy, a presumptive mechanism for learning and memory, is present in this cortical region. Here we address this issue by examining the induction of synaptic plasticity in surgically resected human inferior and middle temporal cortex. The results show that synaptic strength in the human temporal cortex could undergo bidirectional modifications, depending on the pattern of conditioning stimulation. High frequency stimulation (100 or 40 Hz) in layer IV induced long-term potentiation (LTP) of both intracellular excitatory postsynaptic potentials and evoked field potentials in layers II/III. The LTP induced by 100 Hz tetanus was blocked by 50-100 microM DL-2-amino-5-phosphonovaleric acid, suggesting that N-methyl-D-aspartate receptors were responsible for its induction. Long-term depression (LTD) was elicited by prolonged low frequency stimulation (1 Hz, 15 min). It was reduced, but not completely blocked, by DL-2-amino-5-phosphonovaleric acid, implying that some other mechanisms in addition to N-methyl-DL-aspartate receptors were involved in LTD induction. LTD was input-specific, i.e., low frequency stimulation of one pathway produced LTD of synaptic transmission in that pathway only. Finally, the LTP and LTD could reverse each other, suggesting that they can act cooperatively to modify the functional state of cortical network. These results suggest that LTP and LTD are possible mechanisms for the visual memory and pattern recognition functions performed in the human temporal cortex.

Eradication of human hepatic and pulmonary melanoma metastases in SCID mice by antibody-interleukin 2 fusion proteins.

Antibody-cytokine fusion proteins combine the unique targeting ability of antibodies with the multifunctional activity of cytokines. Here, we demonstrate the therapeutic efficacy of such constructs for the treatment of hepatic and pulmonary metastases of different melanoma cell lines. Two antibody-interleukin 2 (IL-2) fusion proteins, ch225-IL2 and ch14.18-IL2, constructed by fusion of a synthetic sequence coding for human IL-2 to the carboxyl end of the Cgamma1 gene of the corresponding antibodies, were tested for their therapeutic efficacy against xenografted human melanoma in vivo. Tumor-specific fusion proteins completely inhibited the growth of hepatic and pulmonary metastases in C.B-17 scid/scid mice previously reconstituted with human lymphokine-activated killer cells, whereas treatment with combinations of the corresponding antibodies plus recombinant IL-2 only reduced the tumor load. Even when treatment with fusion proteins was delayed up to 8 days after inoculation of tumor cells, it still resulted in complete eradication of micrometastases that were established at that time point. Selection of tumor cell lines expressing or lacking the targeted antigen of the administered fusion protein proved the specificity of the observed antitumor effect. Biodistribution analysis demonstrated that the tumor-specific fusion protein accumulated not only in subcutaneous tumors but also in lungs and livers affected with micrometastases. Survival times of animals treated with the fusion protein were more than doubled as compared to those treated with the combination of the corresponding antibody plus IL-2. Our data demonstrate that an immunotherapeutic approach using cytokines targeted by antibodies to tumor sites has potent effects against disseminated human melanoma.

Human naive and memory T lymphocytes differ in telomeric length and replicative potential.

The present study has assessed the replicative history and the residual replicative potential of human naive and memory T cells. Telomeres are unique terminal chromosomal structures whose length has been shown to decrease with cell division in vitro and with increased age in vivo for human somatic cells. We therefore assessed telomere length as a measure of the in vivo replicative history of naive and memory human T cells. Telomeric terminal restriction fragments were found to be 1.4 +/- 0.1 kb longer in CD4+ naive T cells than in memory cells from the same donors, a relationship that remained constant over a wide range of donor age. These findings suggest that the differentiation of memory cells from naive precursors occurs with substantial clonal expansion and that the magnitude of this expansion is, on average, similar over a wide range of age. In addition, when replicative potential was assessed in vitro, it was found that the capacity of naive cells for cell division was 128-fold greater as measured in mean population doublings than the capacity of memory cells from the same individuals. Human CD4+ naive and memory cells thus differ in in vivo replicative history, as reflected in telomeric length, and in their residual replicative capacity.

Molecular characterization of a second melatonin receptor expressed in human retina and brain: the Mel1b melatonin receptor.

A G protein-coupled receptor for the pineal hormone melatonin was recently cloned from mammals and designated the Mel1a melatonin receptor. We now report the cloning of a second G protein-coupled melatonin receptor from humans and designate it the Mel1b melatonin receptor. The Mel1b receptor cDNA encodes a protein of 362 amino acids that is 60% identical at the amino acid level to the human Mel1a receptor. Transient expression of the Mel1b receptor in COS-1 cells results in high-affinity 2-[125I]iodomelatonin binding (Kd = 160 +/- 30 pM). In addition, the rank order of inhibition of specific 2-[125I]iodomelatonin binding by eight ligands is similar to that exhibited by the Mel1a melatonin receptor. Functional studies of NIH 3T3 cells stably expressing the Mel1b melatonin receptor indicate that it is coupled to inhibition of adenylyl cyclase. Comparative reverse transcription PCR shows that the Mel1b melatonin receptor is expressed in retina and, to a lesser extent, brain. PCR analysis of human-rodent somatic cell hybrids maps the Mel1b receptor gene (MTNR1B) to human chromosome 11q21-22. The Mel1b melatonin receptor may mediate the reported actions of melatonin in retina and participate in some of the neurobiological effects of melatonin in mammals.

The Lutheran blood group glycoprotein, another member of the immunoglobulin superfamily, is widely expressed in human tissues and is developmentally regulated in human liver.

Glycoproteins expressing the Lutheran blood group antigens were isolated from human erythrocyte membranes and from human fetal liver. Amino acid sequence analyses allowed the design of redundant oligonucleotides that were used to generate a 459-bp, sequence-specific probe by PCR. A cDNA clone of 2400 bp was isolated from a human placental lambda gt 11 library and sequenced, and the deduced amino acid sequence was studied. The predicted mature protein is a type I membrane protein of 597 amino acids with five potential N-glycosylation sites. There are five disulfide-bonded, extracellular, immunoglobulin superfamily domains (two variable-region set and three constant-region set), a single hydrophobic, membrane-spanning domain, and a cytoplasmic domain of 59 residues. The overall structure is similar to that of the human tumor marker MUC 18 and the chicken neural adhesion molecule SC1. The extracellular domains and cytoplasmic domain contain consensus motifs for the binding of integrin and Src homology 3 domains, respectively, suggesting possible receptor and signal-transduction function. Immunostaining of human tissues demonstrated a wide distribution and provided evidence that the glycoprotein is under developmental control in liver and may also be regulated during differentiation in other tissues.

Three-dimensional scroll waves of cAMP could direct cell movement and gene expression in Dictyostelium slugs.

Complex three-dimensional waves of excitation can explain the observed cell movement pattern in Dictyostelium slugs. Here we show that these three-dimensional waves can be produced by a realistic model for the cAMP relay system [Martiel, J. L. & Goldbeter, A. (1987) Biophys J. 52, 807-828]. The conversion of scroll waves in the prestalk zone of the slug into planar wave fronts in the prespore zone can result from a smaller fraction of relaying cells in the prespore zone. Further, we show that the cAMP concentrations to which cells in a slug are exposed over time display a simple pattern, despite the complex spatial geometry of the waves. This cAMP distribution agrees well with observed patterns of cAMP-regulated cell type-specific gene expression. The core of the spiral, which is a region of low cAMP concentration, might direct expression of stalk-specific genes during culmination.