A tonically active master neuron modulates mutually exclusive motor states at two timescales

Continuity of behaviors requires animals to make smooth transitions between mutually exclusive behavioral states. Neural principles that govern these transitions are not well understood. Caenorhabditis elegans spontaneously switch between two opposite motor states, forward and backward movement, a phenomenon thought to reflect the reciprocal inhibition between interneurons AVB and AVA. Here, we report that spontaneous locomotion and their corresponding motor circuits are not separately controlled. AVA and AVB are neither functionally equivalent nor strictly reciprocally inhibitory. AVA, but not AVB, maintains a depolarized membrane potential. While AVA phasically inhibits the forward promoting interneuron AVB at a fast timescale, it maintains a tonic, extrasynaptic excitation on AVB over the longer timescale. We propose that AVA, with tonic and phasic activity of opposite polarities on different timescales, acts as a master neuron to break the symmetry between the underlying forward and backward motor circuits. This master neuron model offers a parsimonious solution for sustained locomotion consisted of mutually exclusive motor states.

UBR-1 ubiquitin ligase regulates the balance between GABAergic and glutamatergic signaling

Excitation/inhibition (E/I) balance is carefully maintained by the nervous system. The neurotransmitter GABA has been reported to be co-released with its sole precursor, the neurotransmitter glutamate. The genetic and circuitry mechanisms to establish the balance between GABAergic and glutamatergic signaling have not been fully elucidated. Caenorhabditis elegans DVB is an excitatory GABAergic motoneuron that drives the expulsion step in the defecation motor program. We show here that in addition to UNC-47, the vesicular GABA transporter, DVB also expresses EAT-4, a vesicular glutamate transporter. UBR-1, a conserved ubiquitin ligase, regulates DVB activity by suppressing a bidirectional inhibitory glutamate signaling. Loss of UBR-1 impairs DVB Ca2+ activity and expulsion frequency. These impairments are fully compensated by the knockdown of EAT-4 in DVB. Further, glutamate-gated chloride channels GLC-3 and GLC-2/4 receive DVB's glutamate signals to inhibit DVB and enteric muscle activity, respectively. These results implicate an intrinsic cellular mechanism that promotes the inherent asymmetric neural activity. We propose that elevated glutamate in ubr-1 mutants, being the cause of the E/I shift, potentially contributes to Johanson Blizzard syndrome.

Functional imaging and quantification of multineuronal olfactory responses in C. elegans

Many animals perceive odorant molecules by collecting information from ensembles of olfactory neurons, where each neuron uses receptors that are tuned to recognize certain odorant molecules with different binding affinity. Olfactory systems are able, in principle, to detect and discriminate diverse odorants using combinatorial coding strategies. We have combined microfluidics and multineuronal imaging to study the ensemble-level olfactory representations at the sensory periphery of the nematode Caenorhabditis elegans. The collective activity of C. elegans chemosensory neurons reveals high-dimensional representations of olfactory information across a broad space of odorant molecules. We reveal diverse tuning properties and dose-response curves across chemosensory neurons and across odorants. We describe the unique contribution of each sensory neuron to an ensemble-level code for volatile odorants. We show that a natural stimuli, a set of nematode pheromones, are also encoded by the sensory ensemble. The integrated activity of the C. elegans chemosensory neurons contains sufficient information to robustly encode the intensity and identity of diverse chemical stimuli.

Extrasynaptic signaling enables an asymmetric juvenile motor circuit to produce symmetric undulation

In many animals, there is a direct correspondence between the motor patterns that drive locomotion and the motor neuron innervation. For example, the adult C. elegans moves with symmetric and alternating dorsal-ventral bending waves arising from symmetric motor neuron input onto the dorsal and ventral muscles. In contrast to the adult, the C. elegans motor circuit at the juvenile larval stage has asymmetric wiring between motor neurons and muscles but still generates adult-like bending waves with dorsal-ventral symmetry. We show that in the juvenile circuit, wiring between excitatory and inhibitory motor neurons coordinates the contraction of dorsal muscles with relaxation of ventral muscles, producing dorsal bends. However, ventral bending is not driven by analogous wiring. Instead, ventral muscles are excited uniformly by premotor interneurons through extrasynaptic signaling. Ventral bends occur in anti-phasic entrainment to activity of the same motor neurons that drive dorsal bends. During maturation, the juvenile motor circuit is replaced by two motor subcircuits that separately drive dorsal and ventral bending. Modeling reveals that the juvenile's immature motor circuit is an adequate solution to generate adult-like dorsal-ventral bending before the animal matures. Developmental rewiring between functionally degenerate circuit solutions, which both generate symmetric bending patterns, minimizes behavioral disruption across maturation.

Escape steering by cholecystokinin peptidergic signaling

Escape is an evolutionarily conserved and essential avoidance response. Considered to be innate, most studies on escape responses focused on hard-wired circuits. We report here that a neuropeptide NLP-18 and its cholecystokinin receptor CKR-1 enable the escape circuit to execute a full omega (Ω) turn. We demonstrate in vivo NLP-18 is mainly secreted by the gustatory sensory neuron (ASI) to activate CKR-1 in the head motor neuron (SMD) and the turn-initiating interneuron (AIB). Removal of NLP-18 or CKR-1 or specific knockdown of CKR-1 in SMD or AIB neurons leads to shallower turns, hence less robust escape steering. Consistently, elevation of head motor neuron (SMD)'s Ca²⁺ transients during escape steering is attenuated upon the removal of NLP-18 or CKR-1. In vitro, synthetic NLP-18 directly evokes CKR-1-dependent currents in oocytes and CKR-1-dependent Ca²⁺ transients in SMD. Thus, cholecystokinin peptidergic signaling modulates an escape circuit to generate robust escape steering.

Natural sensory context drives diverse brain-wide activity during C. elegans mating

Natural goal-directed behaviors often involve complex sequences of many stimulus-triggered components. Understanding how brain circuits organize such behaviors requires mapping the interactions between an animal, its environment, and its nervous system. Here, we use brain-wide neuronal imaging to study the full performance of mating by the C. elegans male. We show that as mating unfolds in a sequence of component behaviors, the brain operates similarly between instances of each component but distinctly between different components. When the full sensory and behavioral context is taken into account, unique roles emerge for each neuron. Functional correlations between neurons are not fixed but change with behavioral dynamics. From individual neurons to circuits, our study shows how diverse brain-wide dynamics emerge from the integration of sensory perception and motor actions in their natural context.

Corollary discharge promotes a sustained motor state in a neural circuit for navigation

Animals exhibit behavioral and neural responses that persist on longer timescales than transient or fluctuating stimulus inputs. Here, we report that Caenorhabditis elegans uses feedback from the motor circuit to a sensory processing interneuron to sustain its motor state during thermotactic navigation. By imaging circuit activity in behaving animals, we show that a principal postsynaptic partner of the AFD thermosensory neuron, the AIY interneuron, encodes both temperature and motor state information. By optogenetic and genetic manipulation of this circuit, we demonstrate that the motor state representation in AIY is a corollary discharge signal. RIM, an interneuron that is connected with premotor interneurons, is required for this corollary discharge. Ablation of RIM eliminates the motor representation in AIY, allows thermosensory representations to reach downstream premotor interneurons, and reduces the animal's ability to sustain forward movements during thermotaxis. We propose that feedback from the motor circuit to the sensory processing circuit underlies a positive feedback mechanism to generate persistent neural activity and sustained behavioral patterns in a sensorimotor transformation.

Flexible motor sequence generation during stereotyped escape responses

Complex animal behaviors arise from a flexible combination of stereotyped motor primitives. Here we use the escape responses of the nematode Caenorhabditis elegans to study how a nervous system dynamically explores the action space. The initiation of the escape responses is predictable: the animal moves away from a potential threat, a mechanical or thermal stimulus. But the motor sequence and the timing that follow are variable. We report that a feedforward excitation between neurons encoding distinct motor states underlies robust motor sequence generation, while mutual inhibition between these neurons controls the flexibility of timing in a motor sequence. Electrical synapses contribute to feedforward coupling whereas glutamatergic synapses contribute to inhibition. We conclude that C. elegans generates robust and flexible motor sequences by combining an excitatory coupling and a winner-take-all operation via mutual inhibition between motor modules.

An Upconversion Nanoparticle Enables Near Infrared-Optogenetic Manipulation of the Caenorhabditis elegans Motor Circuit

Near-infrared (NIR) light penetrates tissue deeply, but its application to motor behavior stimulation has been limited by the lack of known genetic NIR light-responsive sensors. We designed and synthesized a Yb³⁺/Er³⁺/Ca²⁺-based lanthanide-doped upconversion nanoparticle (UCNP) that effectively converts 808 nm NIR light to green light emission. This UCNP is compatible with Chrimson, a cation channel activated by green light; as such, it can be used in the optogenetic manipulation of the motor behaviors of Caenorhabditis elegans. We show that this UCNP effectively activates Chrimson-expressing, inhibitory GABAergic motor neurons, leading to reduced action potential firing in the body wall muscle and resulting in locomotion inhibition. The UCNP also activates the excitatory glutamatergic DVC interneuron, leading to potentiated muscle action potential bursts and active reversal locomotion. Moreover, this UCNP exhibits negligible toxicity in neural development, growth, and reproduction, and the NIR energy required to elicit these behavioral and physiological responses does not activate the animal's temperature response. This study shows that UCNP provides a useful integrated optogenetic toolset, which may have wide applications in other experimental systems.

Excitatory motor neurons are local oscillators for backward locomotion

Cell- or network-driven oscillators underlie motor rhythmicity. The identity of C. elegans oscillators remains unknown. Through cell ablation, electrophysiology, and calcium imaging, we show: (1) forward and backward locomotion is driven by different oscillators; (2) the cholinergic and excitatory A-class motor neurons exhibit intrinsic and oscillatory activity that is sufficient to drive backward locomotion in the absence of premotor interneurons; (3) the UNC-2 P/Q/N high-voltage-activated calcium current underlies A motor neuron's oscillation; (4) descending premotor interneurons AVA, via an evolutionarily conserved, mixed gap junction and chemical synapse configuration, exert state-dependent inhibition and potentiation of A motor neuron's intrinsic activity to regulate backward locomotion. Thus, motor neurons themselves derive rhythms, which are dually regulated by the descending interneurons to control the reversal motor state. These and previous findings exemplify compression: essential circuit properties are conserved but executed by fewer numbers and layers of neurons in a small locomotor network.

Neuroendocrine modulation sustains the C. elegans forward motor state

Neuromodulators shape neural circuit dynamics. Combining electron microscopy, genetics, transcriptome profiling, calcium imaging, and optogenetics, we discovered a peptidergic neuron that modulates C. elegans motor circuit dynamics. The Six/SO-family homeobox transcription factor UNC-39 governs lineage-specific neurogenesis to give rise to a neuron RID. RID bears the anatomic hallmarks of a specialized endocrine neuron: it harbors near-exclusive dense core vesicles that cluster periodically along the axon, and expresses multiple neuropeptides, including the FMRF-amide-related FLP-14. RID activity increases during forward movement. Ablating RID reduces the sustainability of forward movement, a phenotype partially recapitulated by removing FLP-14. Optogenetic depolarization of RID prolongs forward movement, an effect reduced in the absence of FLP-14. Together, these results establish the role of a neuroendocrine cell RID in sustaining a specific behavioral state in C. elegans.

DOI:http://dx.doi.org/10.7554/eLife.19887.001

The long and the short of SAD-1 kinase

The Ser/Thr SAD kinases are evolutionarily conserved, critical regulators of neural development. Exciting findings in recent years have significantly advanced our understanding of the mechanism through which SAD kinases regulate neural development. Mammalian SAD-A and SAD-B, activated by a master kinase LKB1, regulate microtubule dynamics and polarize neurons. In C. elegans, the sad-1 gene encodes two isoforms, namely the long and the short, which exhibit overlapping and yet distinct functions in neuronal polarity and synaptic organization. Surprisingly, our most recent findings in C. elegans revealed a SAD-1-independent LKB1 activity in neuronal polarity. We also found that the long SAD-1 isoform directly interacts with a STRADalpha pseudokinase, STRD-1, to regulate neuronal polarity and synaptic organization. We elaborate here a working model of SAD-1 in which the two isoforms dimer/oligomerize to form a functional complex, and STRD-1 clusters and localizes the SAD-1 complex to synapses. While the mechanistic difference between the vertebrate and invertebrate SAD kinases may be puzzling, a recent discovery of the functionally distinct SAD-B isoforms predicts that the difference likely arises from our incomplete understanding of the SAD kinase mechanism and may eventually be reconciled as the revelation continues.

A co-operative regulation of neuronal excitability by UNC-7 innexin and NCA/NALCN leak channel

Gap junctions mediate the electrical coupling and intercellular communication between neighboring cells. Some gap junction proteins, namely connexins and pannexins in vertebrates, and innexins in invertebrates, may also function as hemichannels. A conserved NCA/Dmα1U/NALCN family cation leak channel regulates the excitability and activity of vertebrate and invertebrate neurons. In the present study, we describe a genetic and functional interaction between the innexin UNC-7 and the cation leak channel NCA in Caenorhabditis elegans neurons. While the loss of the neuronal NCA channel function leads to a reduced evoked postsynaptic current at neuromuscular junctions, a simultaneous loss of the UNC-7 function restores the evoked response. The expression of UNC-7 in neurons reverts the effect of the unc-7 mutation; moreover, the expression of UNC-7 mutant proteins that are predicted to be unable to form gap junctions also reverts this effect, suggesting that UNC-7 innexin regulates neuronal activity, in part, through gap junction-independent functions. We propose that, in addition to gap junction-mediated functions, UNC-7 innexin may also form hemichannels to regulate C. elegans' neuronal activity cooperatively with the NCA family leak channels.

C. elegans STRADalpha and SAD cooperatively regulate neuronal polarity and synaptic organization

Neurons are polarized cells with morphologically and functionally distinct axons and dendrites. The SAD kinases are crucial for establishing the axon-dendrite identity across species. Previous studies suggest that a tumour suppressor kinase, LKB1, in the presence of a pseudokinase, STRADalpha, initiates axonal differentiation and growth through activating the SAD kinases in vertebrate neurons. STRADalpha was implicated in the localization, stabilization and activation of LKB1 in various cell culture studies. Its in vivo functions, however, have not been examined. In our present study, we analyzed the neuronal phenotypes of the first loss-of-function mutants for STRADalpha and examined their genetic interactions with LKB1 and SAD in C. elegans. Unexpectedly, only the C. elegans STRADalpha, STRD-1, functions exclusively through the SAD kinase, SAD-1, to regulate neuronal polarity and synaptic organization. Moreover, STRD-1 tightly associates with SAD-1 to coordinate its synaptic localizations. By contrast, the C. elegans LKB1, PAR-4, also functions in an additional genetic pathway independently of SAD-1 and STRD-1 to regulate neuronal polarity. We propose that STRD-1 establishes neuronal polarity and organizes synaptic proteins in a complex with the SAD-1 kinase. Our findings suggest that instead of a single, linear genetic pathway, STRADalpha and LKB1 regulate neuronal development through multiple effectors that are shared in some cellular contexts but distinct in others.

A putative cation channel, NCA-1, and a novel protein, UNC-80, transmit neuronal activity in C. elegans

Voltage-gated cation channels regulate neuronal excitability through selective ion flux. NALCN, a member of a protein family that is structurally related to the alpha1 subunits of voltage-gated sodium/calcium channels, was recently shown to regulate the resting membrane potentials by mediating sodium leak and the firing of mouse neurons. We identified a role for the Caenorhabditis elegans NALCN homologues NCA-1 and NCA-2 in the propagation of neuronal activity from cell bodies to synapses. Loss of NCA activities leads to reduced synaptic transmission at neuromuscular junctions and frequent halting in locomotion. In vivo calcium imaging experiments further indicate that while calcium influx in the cell bodies of egg-laying motorneurons is unaffected by altered NCA activity, synaptic calcium transients are significantly reduced in nca loss-of-function mutants and increased in nca gain-of-function mutants. NCA-1 localizes along axons and is enriched at nonsynaptic regions. Its localization and function depend on UNC-79, and UNC-80, a novel conserved protein that is also enriched at nonsynaptic regions. We propose that NCA-1 and UNC-80 regulate neuronal activity at least in part by transmitting depolarization signals to synapses in C. elegans neurons.

Markovian timed Petri nets for performance analysis of semiconductor manufacturing systems

A subclass of generalized stochastic Petri nets (GSPNs) with priorities, called Markovian timed Petri nets, are proposed to model semiconductor manufacturing systems that consider process priorities, routing priorities, resource re-entrance, and nonpreemptive operations. Uniformization technique is used to establish both lower and upper bounds of the performance of interest. These bounds are computable using linear programming. Numerical experiments have been conducted to evaluate the accuracy of the bounds using models adapted from real-world systems. The experiments show that the upper bounds are very close to the simulation results. Thus, performance measures can be accurately estimated using these bounds.

Neuronal polarity is regulated by a direct interaction between a scaffolding protein, Neurabin, and a presynaptic SAD-1 kinase in Caenorhabditis elegans

The establishment of axon-dendrite identity in developing neurites is essential for the development of a functional nervous system. The SAD serine-threonine kinases have been implicated in regulating neuronal polarization and synapse formation. Here, we show that the C. elegans SAD-1 kinase regulates axonal identity and synapse formation through distinct mechanisms. We identified a scaffolding protein, Neurabin (NAB-1), as a physiological binding partner of SAD-1. Both sad-1 and nab-1 loss-of-function mutants display polarity defects in which synaptic vesicles accumulate in both axons and dendrites. We show that sad-1 and nab-1 function in the same genetic pathway to restrict axonal fate. Unlike sad-1, nab-1 mutants display normal morphology of vesicle clusters. Strikingly, although the physical interaction of NAB-1 with SAD-1 is necessary for polarity, it is dispensable for synapse morphology. We propose that Neurabin functions as a scaffold to facilitate SAD-1-mediated phosphorylation for substrates specific for restricting axonal fate during neuronal polarization.

Thyroglossal duct cyst: an infrequently considered diagnosis in pediatric patients with anterior neck masses

OBJECTIVE

To describe a pediatric patient with an anterior neck mass and discuss the evaluation and treatment.

METHODS

We present a case report and a discussion of the differential diagnosis of anterior cervical masses. The workup and therapy for an anterior neck mass, which was a thyroglossal duct cyst, are reviewed.

RESULTS

A thyroglossal duct cyst in pediatric patients is an uncommon finding. For establishing a correct diagnosis, surgical confirmation is necessary. Identification is important because of the high incidence of misdiagnosis, recurrent infections, inadequate treatment, and possible neoplastic change.

CONCLUSION

A thyroglossal duct cyst should be included in the differential diagnosis of an anterior neck mass. Recommended treatment consists of surgical removal of the cyst, the entire thyroglossal duct tract, and the central portion of the hyoid bone.

An SCF-like ubiquitin ligase complex that controls presynaptic differentiation

During synapse formation, specialized subcellular structures develop at synaptic junctions in a tightly regulated fashion. Cross-signalling initiated by ephrins, Wnts and transforming growth factor-beta family members between presynaptic and postsynaptic termini are proposed to govern synapse formation. It is not well understood how multiple signals are integrated and regulated by developing synaptic termini to control synaptic differentiation. Here we report the identification of FSN-1, a novel F-box protein that is required in presynaptic neurons for the restriction and/or maturation of synapses in Caenorhabditis elegans. Many F-box proteins are target recognition subunits of SCF (Skp, Cullin, F-box) ubiquitin-ligase complexes. fsn-1 functions in the same pathway as rpm-1, a gene encoding a large protein with RING finger domains. FSN-1 physically associates with RPM-1 and the C. elegans homologues of SKP1 and Cullin to form a new type of SCF complex at presynaptic periactive zones. We provide evidence that T10H9.2, which encodes the C. elegans receptor tyrosine kinase ALK (anaplastic lymphoma kinase), may be a target or a downstream effector through which FSN-1 stabilizes synapse formation. This neuron-specific, SCF-like complex therefore provides a localized signal to attenuate presynaptic differentiation.

Constitutive activation of met kinase in non-small-cell lung carcinomas correlates with anchorage-independent cell survival

Lung cancer is currently the most frequent cause of cancer death in North America. Hepatocyte growth factor (HGF) and its receptor Met are frequently over-expressed in non-small-cell lung carcinomas (NSCLC), but their potential role in tumor progression is not clearly known. To assess the role of HGF/Met signaling in lung carcinomas, we have examined the expression, activation status, and function of Met in NSCLC cell lines (n = 7), established from primary tumors or pleural fluids of cancer patients. We observed Met expression in three NSCLC cell lines, two of which exhibited constitutive tyrosine-phosphorylation of Met, and Met kinase activity. In addition, the observed constitutive activation of Met was sustained under anchorage-independent conditions, and correlated with phosphatidyl inositol 3-kinase-dependent cell survival. Immunoreactive HGF-like protein was secreted by two Met-positive and two Met-negative NSCLC cell lines. However HGF activity, as determined by the ability to induce cell scattering and tyrosine-phosphorylation of Met in reporter cell lines, was detected in conditioned medium from only one Met-negative NSCLC cell line: none of the conditioned media from Met-expressing NSCLC cell lines showed detectable HGF activity. Thus, constitutive activation of Met in NSCLC cell lines may occur at least in part through intracrine, or HGF-independent mechanisms. Interestingly, additional paracrine stimulation with exogenous recombinant HGF was required for DNA synthesis and correlated with increased activation of ERK1/2 in all Met-positive NSCLC cell lines, regardless of the basal activation status of Met. These findings indicate that a medium level of constitutive activation of Met occurs in some NSCLC cell lines, and correlates with survival of detached carcinoma cells; whereas additional paracrine stimulation by recombinant HGF is required for DNA synthesis. Thus constitutive and paracrine activation of Met may provide complementary signals that promote survival and proliferation, respectively, during tumor progression of NSCLC.

Srb10/Cdk8 regulates yeast filamentous growth by phosphorylating the transcription factor Ste12

The budding yeast Saccharomyces cerevisiae differentiates into filamentous invasively growing forms under conditions of nutrient limitation. This response is dependent on the transcription factor Ste12 and on the mating pheromone-response mitogen-activated protein (MAP) kinase cascade, but a mechanism for regulation of Ste12 by nutrient limitation has not been defined. Here we show that Ste12 function in filamentous growth is regulated by the cyclin-dependent kinase Srb10 (also known as Cdk8), which is associated with the RNA polymerase II holoenzyme. Srb10 inhibits filamentous growth in cells growing in rich medium by phosphorylating Ste12 and decreasing its stability. Under conditions of limiting nitrogen, loss of Srb10 protein and kinase activity occurs, with a corresponding loss of Ste12 phosphorylation. Mutation of the Srb10-dependent phosphorylation sites increases pseudohyphal development but has no effect on the pheromone response of haploid yeast. Srb10 kinase activity is also regulated independently of the mating pheromone-response pathway. This indicates that Srb10 controls Ste12 activity for filamentous growth in response to nitrogen limitation and is consistent with the hypothesis that Srb10 regulates gene-specific activators in response to physiological signals to coordinate gene expression with growth potential.

Altered p27(Kip1) phosphorylation, localization, and function in human epithelial cells resistant to transforming growth factor beta-mediated G(1) arrest

p27(Kip1) is an important effector of G(1) arrest by transforming growth factor beta (TGF-beta). Investigations in a human mammary epithelial cell (HMEC) model, including cells that are sensitive (184(S)) and resistant (184A1L5(R)) to G(1) arrest by TGF-beta, revealed aberrant p27 regulation in the resistant cells. Cyclin E1-cyclin-dependent kinase 2 (cdk2) and cyclin A-cdk2 activities were increased, and p27-associated kinase activity was detected in 184A1L5(R) cells. p27 from 184A1L5(R) cells was localized to both nucleus and cytoplasm, showed an altered profile of phosphoisoforms, and had a reduced ability to bind and inhibit cyclin E1-cdk2 in vitro when compared to p27 from the sensitive 184(S) cells. In proliferating 184A1L5(R) cells, more p27 was associated with cyclin D1-cdk4 complexes than in 184(S). While TGF-beta inhibited the formation of cyclin D1-cdk4-p27 complexes in 184(S) cells, it did not inhibit the assembly of cyclin D1-cdk4-p27 complexes in the resistant 184A1L5(R) cells. p27 phosphorylation changed during cell cycle progression, with cyclin E1-bound p27 in G(0) showing a different phosphorylation pattern from that of cyclin D1-bound p27 in mid-G(1). These data suggest a model in which TGF-beta modulates p27 phosphorylation from its cyclin D1-bound assembly phosphoform to an alternate form that binds tightly to inhibit cyclin E1-cdk2. Altered phosphorylation of p27 in the resistant 184A1L5(R) cells may favor the binding of p27 to cyclin D1-cdk4 and prevent its accumulation in cyclin E1-cdk2 in response to TGF-beta.

Co-operative effect of c-Src tyrosine kinase and Stat3 in activation of hepatocyte growth factor expression in mammary carcinoma cells

We have previously shown coexpression of hepatocyte growth factor (HGF) and its receptor Met in the invasive tumor front of human breast carcinomas. We have also demonstrated secretion of HGF, constitutive activation of Met, and increased invasion in a murine breast carcinoma cell line, SP1. These observations suggest the presence of an HGF autocrine loop in some breast carcinoma cells, which confers increased survival, growth, and invasiveness during tumor progression and metastasis. c-Src tyrosine kinase, which is critical in regulating the expression of many genes, is activated in SP1 carcinoma cells, as well as in most human breast cancers. We therefore examined the role of c-Src kinase in HGF expression in breast carcinoma cells. Expression of activated c-Src in SP1 cells increased transcription from the HGF promoter and expression of HGF mRNA and protein, while dominant negative c-Src had the opposite effect. Using deletion analysis, we showed that the region between -254 and -70 base pairs was required for c-Src responsiveness of the HGF promoter. This region contains two putative consensus sequences (at -110 and -149 base pairs) for the Stat3 transcription factor, which bind protein complexes containing Stat3 (but not Stat1, -5A, or -5B). Coexpression of activated c-Src and Stat3 synergistically induced strong HGF promoter activity in SP1 cells, as well as in a nonmalignant epithelial cell line, HC11 (HGF negative). c-Src kinase activity correspondingly increased the tyrosine 705 phosphorylation and DNA binding affinity of Stat3 (but not Stat1, -5A, or -5B). Collectively, our data indicate a cooperative effect of c-Src kinase and Stat3 in the activation of HGF transcription and protein expression in breast carcinoma cells. This process may be important in overriding the strong repression of HGF expression in nonmalignant epithelium, and thereby promote tumorigenesis.

Two regulators of Ste12p inhibit pheromone-responsive transcription by separate mechanisms

The yeast Saccharomyces cerevisiae transcription factor Ste12p is responsible for activating genes in response to MAP kinase cascades controlling mating and filamentous growth. Ste12p is negatively regulated by two inhibitor proteins, Dig1p (also called Rst1p) and Dig2p (also called Rst2p). The expression of a C-terminal Ste12p fragment (residues 216 to 688) [Ste12p(216-688)] from a GAL promoter causes FUS1 induction in a strain expressing wild-type STE12, suggesting that this region can cause the activation of endogenous Ste12p. Residues 262 to 594 are sufficient to cause STE12-dependent FUS1 induction when overexpressed, and this region of Ste12p was found to bind Dig1p but not Dig2p in yeast extracts. In contrast, recombinant glutathione S-transferase-Dig2p binds to the Ste12p DNA-binding domain (DBD). Expression of DIG2, but not DIG1, from a GAL promoter inhibits transcriptional activation by an Ste12p DBD-VP16 fusion. Furthermore, disruption of dig1, but not dig2, causes elevated transcriptional activation by a LexA-Ste12p(216-688) fusion. Ste12p has multiple regions within the C terminus (flanking residue 474) that can promote multimerization in vitro, and we demonstrate that these interactions can contribute to the activation of endogenous Ste12p by overproduced C-terminal fragments. These results demonstrate that Dig1p and Dig2p do not function by redundant mechanisms but rather inhibit pheromone-responsive transcription through interactions with separate regions of Ste12p.

Solitary thyroid nodules in 93 children and adolescents. a 35-years experience

Over a period of 35 years from 1963 to 1998, 93 patients under the age of 18 years, 74 girls and 19 boys, were seen for evaluation of a solitary nodule of the thyroid gland. All patients had preoperative scintiscans of the thyroid gland and had their solitary nodule excised. Seventy-seven of the patients had a cold nodule on scintiscanning. The most common cause of solitary thyroid nodules was follicuar adenoma (68.9%). Fifteen of the 77 cold nodules were malignant (19.9%). The frequency of carcinoma in males was 26.3%, while in females it was 13.5%. Our experience suggests that the incidence of thyroid carcinoma may be decreasing in pediatric patients not exposed to known risk factors. Available diagnostic methods for attempting differentiation of benign from malignant solitary nodules are reviewed and recommendations to the clinical management are presented.

c-Src kinase activity is required for hepatocyte growth factor-induced motility and anchorage-independent growth of mammary carcinoma cells

Overexpression and amplification of hepatocyte growth factor (HGF) receptor (Met) have been detected in many types of human cancers, suggesting a critical role for Met in growth and development of malignant cells. However, the molecular mechanism by which Met contributes to tumorigenesis is not well known. The tyrosine kinase c-Src has been implicated as a modulator of cell proliferation, spreading, and migration; these functions are also regulated by Met. To explore whether c-Src kinase is involved in HGF-induced cell growth, a mouse mammary carcinoma cell line (SP1) that co-expresses HGF and Met and a nonmalignant epithelial cell line (Mv1Lu) that expresses Met but not HGF were used. In this study, we have shown that c-Src kinase activity is constitutively elevated in SP1 cells and is induced in response to HGF in Mv1Lu cells. In addition, c-Src kinase associates with Met following stimulation with HGF. The enhanced activity of c-Src kinase also correlates with its ability to associate with Met. Expression of a dominant negative double mutant of c-Src (SRC-RF), lacking both kinase activity (K295R) and a regulatory tyrosine residue (Y527F), in SP1 cells significantly reduced c-Src kinase activity and strongly blocked HGF-induced motility and colony growth in soft agar. In contrast, expression of the dominant negative c-Src mutant had no effect on HGF-induced cell proliferation on plastic. Taken together, our data strongly suggest that HGF-induced association of c-Src with Met and c-Src activation play a critical role in HGF-induced cell motility and anchorage-independent growth of mammary carcinomas and further support the notion that the presence of paracrine and autocrine HGF loops contributes significantly to the transformed phenotype of carcinoma cells.

Linkage of a commoner form of recessive amyotrophic lateral sclerosis to chromosome 15q15-q22 markers

Autosomal recessive familial amyotrophic lateral sclerosis (RFALS) is a rare form of ALS that usually presents at an early age with slow progression of symptoms. RFALS is clinically and genetically heterogeneous and the locus of RFALS type 3 was mapped to 2q33 (ALS2) in a single family. We now report linkage of a more-common form of RFALS to chromosome 15q15-q22 markers (ALS5) and show further genetic locus heterogeneity in RFALS. ALS5 is the locus for most families with RFALS and appears to be present in both North African and European populations.

Expression of human pro-matrix metalloproteinase 3 that lacks the N-terminal 34 residues in Escherichia coli: autoactivation and interaction with tissue inhibitor of metalloproteinase 1 (TIMP-1)

Human pro-matrix metalloproteinase 3 (proMMP-3) lacking the N-terminal 34 amino acids and the C-terminal hemopexin-like domain was expressed in E. coli and used to investigate the process of proenzyme activation and its interaction with an endogenous inhibitor TIMP-1 during activation. The truncated precursor was purified from the E. coli extract in the presence of 5mM EGTA. The active 23.5 kDa form was generated simply by exposure to Ca2+ and Zn2+ but not either by Ca2+ alone or by Zn2+ alone. The rate of MMP-3(deltaC) formation was concentration dependent, indicating that autoactivation is a bimolecular reaction. The truncated precursor was able to interact with the N-terminal domain of TIMP-1 without losing the 48 residue-long propeptide. However, upon a longer incubation, the propeptide was slowly processed, indicating that the association of the N-terminally truncated proMMP-3 with TIMP-1 is weaker than that of the fully activated MMP-3 and TIMP-1. These results indicate that the expression of MMP activities is regulated by endogenous inhibitor TIMPs during their activation processes which provide an additional control mechanism of extracellular matrix breakdown.

Characterization of the basal and pheromone-stimulated phosphorylation states of Ste12p

The Saccharomyces cerevisiae transcription factor Ste12p is required for basal and activated expression of pheromone-responsive genes, and for invasive growth in haploid cells. In diploid yeast, Ste12p is implicated in pseudohyphal development. The ability of Ste12p to effect these various responses in three different cell types must require stringent regulation of its transcriptional activation function and interaction with additional transcription factors. We have examined the phosphorylation state of Ste12p in untreated and pheromone-treated haploid cells, and found eight constitutively phosphorylated peptides. Phosphorylation at the constitutive sites does not require the protein kinases of the pheromone-response pathway. Treatment of haploid yeast with mating pheromone causes the appearance of novel relatively minor phosphorylations on Ste12p. Brief [35S]methionine labeling reveals novel pheromone-dependent, electrophoretically slower migrating Ste12p species. Similarly, the sole difference we observe in tryptic phosphopeptides generated from Ste12p from pheromone-treated and untreated cells is the transient appearance of two novel minor hydrophobic phosphopeptides. The pheromone-dependent phosphorylation of Ste12p requires an intact pheromone-response pathway and localization of Ste12p to the nucleus, but does not require the Ste12p DNA-binding domain. We conclude from these experiments that the pheromone-response pathway induces the formation of specific hyperphosphorylation on Ste12p, which can only be detected as apparently minor modifications in vivo. We argue that, if Ste12p is regulated by direct pheromone-responsive phosphorylation, then that phosphorylation must be represented by the two novel phosphopeptides. However, we cannot exclude the possibility that pheromone-responsive transcription is controlled by direct phosphorylation of a target other than Ste12p.

Marked neonatal breast hypertrophy in a male with transient hyperprolactinemia

A male neonate with marked breast hypertrophy associated with transient hyperprolactinemia is reported. The breast hypertrophy resolved when the serum prolactin levels decreased to normal. Ultrasonographic finding of the breast hypertrophy are presented. It is not known if the hyperprolactinemia was etiologically related to the breast hypertrophy.

Differential regulation of EGF production, EGF receptor-binding, and cellular growth by sodium-butyrate in hep3b and plc/prf/5 human hepatoma-cells

Hep3B and PLC/PRF/5 human hepatoma cells express epidermal growth factor (ECF) mRNA and secret this polypeptide growth factor into the culture medium. The production of EGF was inhibited by sodium butyrate in a dose-dependent manner. EGF receptor numbers in both cell lines were increased after treatment with butyrate for 2 days, In addition, the binding affinity of EGF to its receptor was decreased in butyrate-treated PLC/PRF/5 cells while it did not change in Hep3B cells. EGF-stimulated cell growth in PLC/PRF/5 cells was attenuated by sodium butyrate whereas no significant inhibition df cell growth of Hep3B cells was found in the same condition. Our results suggest that EGF acts as an autocrine growth stimulator in human hepatoma cells and sodium butyrate can differentially regulate the responses of hepatoma cells to EGF by modulating the differentiation states of these cells.

Pseudohypoparathyroidism type Ia and growth hormone deficiency in two siblings

Pseudohypoparathyroidism type Ia (PHP type Ia) is associated with several endocrinopathies. We describe two siblings with PHP type Ia, hypothyroidism and growth hormone deficiency (GHD). To our knowledge, these patients are the first to have PHP type Ia and GHD. The defect which is most likely responsible for the three endocrinopathies is a deficiency of the stimulatory guanine nucleotide-binding regulatory protein, Gs.

Inactivation of a yeast transactivator by the fused HIV-1 proteinase: a simple assay for inhibitors of the viral enzyme activity

The human immunodeficiency virus type 1 (HIV-1) proteinase (PR) and its flanking sequences have been fused in frame between the DNA-binding domain and the transcription-activation domain of the yeast protein, GAL4. As has been shown before with the 3C proteinase of Coxsackie virus B3 (CVB3) [Das Mahapatra et al., Proc. Natl. Acad. Sci. USA 89 (1992) 4159-4162], the GAL4::PR fusion protein retains its GAL4 function, providing the PR is inactive. When PR is active, its autocatalytic activity in the hybrid protein is shown to inactivate the transactivation function of GAL4. This provides a simple assay to monitor PR activity. A dose-dependent effect of a potent PR-specific inhibitor is demonstrated in this system and illustrates the sensitivity of the assay. The assay is used for high throughput screening to identify novel inhibitors of the viral PR, and provides a method to generate and analyze mutants and revertants of the PR.

Hereditary isolated glucocorticoid deficiency is associated with abnormalities of the adrenocorticotropin receptor gene

Isolated glucocorticoid deficiency (IGD) is an autosomal recessive disorder characterized by progressive primary adrenal insufficiency, without mineralocorticoid deficiency. The cDNA and gene of the human ACTH receptor were recently cloned. The gene encodes a 297-amino acid protein that belongs to the G protein-coupled superfamily of membrane receptors. We hypothesized that the ACTH receptor gene might be defective in IGD. To examine this, we studied its genomic structure by PCR and direct sequencing in a 5-yr-old proband with the disease, his parents, and grandparents. The proband was a compound heterozygote for two different point mutations, one in each allele: (a) a substitution (C-->T), also found in one allele of the mother and maternal grandmother, which introduced a premature stop codon (TGA) at position 201 of the protein; this mutant receptor lacks its entire carboxy-terminal third and, if expressed, should be unable to transduce the signal; and (b) a substitution (C-->G), also found in one of the paternal alleles, which changed neutral serine120 in the apolar third transmembrane domain of the receptor to a positively charged arginine, probably disrupting the ligand-binding site. Standard ovine corticotropin releasing hormone (oCRH) test in the heterozygote parents and maternal grandmother revealed exaggerated and prolonged ACTH responses, suggestive of subclinical resistance to ACTH. We conclude that IGD in this family appears to be due to defects of the ACTH receptor gene. The oCRH test appears to be useful in ascertaining heterozygosity in this syndrome.

Neurosarcoidosis presenting as secondary amenorrhea in a teenager

Sarcoidosis is a systemic inflammatory disease of unknown etiology characterized by non-caseating epithelioid cell granulomata. The lungs and reticulo-endothelial system are typically involved, and virtually any organ system may be affected. Sarcoidosis involving the central nervous system is relatively uncommon, estimated to occur in approximately 5% of patients with sarcoidosis in the United States, while the incidence throughout the world may be as high as 15%. Hypothalamic dysfunction is the most common manifestation of central nervous system parenchymatous disease in neurosarcoidosis. Polyuria and polydipsia are the most frequently occurring symptoms in patients with sarcoidosis who have dysfunction of the pituitary and hypothalamus. We describe a patient with secondary amenorrhea resulting from neurosarcoidosis involving the pituitary and hypothalamus.

Solitary thyroid nodules in 71 children and adolescents

Seventy-one children and adolescents with a solitary nodule of the thyroid gland were seen over a 27-year period and all had their nodules removed surgically. All of the patients had preoperative thyroid scintiscans, 55 of which showed a cold nodule. The most common cause of solitary thyroid nodules was follicular adenoma. Fourteen of the 55 cold nodules were malignant (25.5%) while no malignancies were present in warm or hot nodules. Available diagnostic methods for attempting differentiation of benign from malignant solitary nodules are reviewed and recommendations to their clinical management as derived from our experience are presented.

The primary empty-sella syndrome and diabetes insipidus in a child

The empty-sella syndrome is uncommon in pediatric patients. Hypothalamic-pituitary dysfunction is common in these patients but involvement of the posterior pituitary gland is very rare. We report a seven-year-old girl with empty-sella syndrome who first developed arginine-vasopressin deficient diabetes insipidus and then anterior pituitary gland deficiency. The empty-sella syndrome should be included among the causes of arginine-vasopressin deficient diabetes insipidus in pediatric patients.

Nodular thyroid disease and thyroid carcinoma

The primary challenge in the management of a solitary nodule of the thyroid or a multinodular thyroid gland is to rule out a malignancy.

Sonography in neonatal congenital adrenal hyperplasia

Adrenal gland size was evaluated in six infants with congenital adrenal hyperplasia. All of the infants had a severe deficiency of the 21-hydroxylase enzyme resulting in the salt-losing form of congenital adrenal hyperplasia. The adrenal measurements were compared with those of 40 consecutive age-matched, asymptomatic infants. Mean adrenal length was 14.4 mm and width was 1.9 mm in asymptomatic infants, whereas in infants with congenital adrenal hyperplasia mean adrenal length was 23.7 mm and width was 5.3 mm. Although infants with congenital adrenal hyperplasia may have normal-sized adrenal glands, mean length measurements of 20 mm or greater and mean width measurements of 4 mm or greater suggest the diagnosis.