Educating for social responsibility: changing the syllabus of developmental biology

Developmental biology is deeply embedded in the social issues of our times. Such topics as cloning, stems cells, reproductive technologies, sex selection, environmental hormone mimics and gene therapy all converge on developmental biology. It is therefore critical that developmental biologists learn about the possible social consequences of their work and of the possible molding of their discipline by social forces. We present two models for integrating social issues into the developmental biology curriculum. One model seeks to place discussions of social issues into the laboratory portion of the curriculum; the other model seeks to restructure the course, such that developmental biology and its social contexts are synthesized directly.     

Enhancement of antidepressant potency by a potentiator of AMPA receptors

1. AMPA receptor potentiators (ARPs) exhibit antidepressant-like activity in preclinical tests (for example, the forced swim test) that are highly predictive of efficacy in humans. Unlike most currently used antidepressants, ARPs do not elevate extracellular levels of biogenic amines (e.g., 5HT, NE) in prefrontal cortex at doses that are active in the forced swim test.2. The present series of experiments examined the effects of combining the ARP, LY 392098, with biogenic amine-based antidepressants in the forced swim test. Male, NIH Swiss mice were placed in a cylinder of water and observed for attempted escape behaviors and immobility.3. LY 392098 dose-dependently decreased immobility as did a range of classical antidepressants. At doses of LY 392098 below those that decreased immobility, this compound significantly increased the potency with which fluoxetine and citalopram (SSRI antidepressants), imipramine (tricyclic antidepressant), duoxetine (norepinephrine/serotonin uptake blocker), nisoxetine (norepinephrine uptake inhibitor), and rolipram (PDE4 inhibitor) decreased immobility in the forced swim test with potency shifts upward of 5-fold (fluoxetine, imipramine, and rolipram). Likewise, ineffective doses of the traditional antidepressants potentiated the effects LY 392098 with shifts in the dose-effect functions that were 10-fold or more for citalopram, fluoxetine, imipramine, and duloxetine.4. Combined with other evidence for a role of AMPA receptors in the efficacy of antidepressants, the current data suggest that the addition of an ARP may augment the activity and perhaps the onset of the therapeutic effects of biogenic amine and second messenger-based antidepressants.     

The N-terminal 24 amino acids of the p55 gamma regulatory subunit of phosphoinositide 3-kinase binds Rb and induces cell cycle arrest

Although phosphoinositide 3-kinase (PI 3-kinase) is essential for cell cycle progression, the molecular mechanisms that regulate its diverse biological effects are poorly understood. We demonstrate here that Rb, a key regulator of cell cycle progression, associates with p55 kDa (p55alpha and p55gamma) regulatory subunits of PI 3-kinase in vivo and in vitro. Both confocal microscopy and biochemical analysis demonstrated the presence of p55gamma in the nucleus. The 24-amino-acid N-terminal end of p55gamma, which is unique among PI 3-kinase regulatory subunits, was sufficient to bind Rb. Addition of serum or growth factors to quiescent cells triggered the dissociation of Rb from p55. Ectopic expression of the 24-amino-acid N-terminal end of p55gamma inhibited cell cycle progression, as evidenced by induction of cell growth arrest at the G0/G1 phase, inhibition of DNA synthesis, inhibition of cyclin D and cyclin E promoter activity, and changes in the expression of cell cycle-related proteins. The inhibitory effects of the N-terminal end of p55gamma on cell cycle progression depended on the presence of functional Rb. These data demonstrate for the first time an association of p55gamma with Rb and show that modification of this association can lead to cell cycle arrest.     

Opposing FGF and retinoid pathways control ventral neural pattern, neuronal differentiation, and segmentation during body axis extension

Vertebrate body axis extension involves progressive generation and subsequent differentiation of new cells derived from a caudal stem zone; however, molecular mechanisms that preserve caudal progenitors and coordinate differentiation are poorly understood. FGF maintains caudal progenitors and its attenuation is required for neuronal and mesodermal differentiation and to position segment boundaries. Furthermore, somitic mesoderm promotes neuronal differentiation in part by downregulating Fgf8. Here we identify retinoic acid (RA) as this somitic signal and show that retinoid and FGF pathways have opposing actions. FGF is a general repressor of differentiation, including ventral neural patterning, while RA attenuates Fgf8 in neuroepithelium and paraxial mesoderm, where it controls somite boundary position. RA is further required for neuronal differentiation and expression of key ventral neural patterning genes. Our data demonstrate that FGF and RA pathways are mutually inhibitory and suggest that their opposing actions provide a global mechanism that controls differentiation during axis extension.     

Hemispheric dissociation in access to the human semantic system

Patient studies suggest that speech and environmental sounds are differentially processed by the left and right hemispheres. Here, using functional imaging in normal subjects, we compared semantic processing of spoken words to equivalent processing of environmental sounds, after controlling for low-level perceptual differences. Words enhanced activation in left anterior and posterior superior temporal regions, while environmental sounds enhanced activation in a right posterior superior temporal region. This left/right dissociation was unchanged by different attentional/working memory contexts, but it was specific to tasks requiring semantic analysis. While semantic processing involves widely distributed networks in both hemispheres, our results support the hypothesis of a dual access route specific for verbal and nonverbal material, respectively.     

6,6'-Dimycoloyl trehalose from a rapidly growing Mycobacterium: an alternative antigen for tuberculosis serodiagnosis

Mycobacterial O-acyltrehaloses have been described as highly specific and sensitive reagents for tuberculosis immunodiagnosis. An O-acyltrehalose-containing lipid fraction from the rapidly growing Mycobacterium fortuitum was found to include additional antigens, which presented high cross-reactivity with sera from tuberculosis-infected patients. Based on a combination of selective chemical degradations, thin-layer-chromatography analyses and (1)H-nuclear magnetic resonance spectroscopy, the antigenic by-product was identified as 6,6'-dimycoloyl trehalose, the so-called cord factor. The lipid was purified and tested in ELISA for pulmonary tuberculosis serodiagnosis. Sensitivity and specificity of the test were found to be 66.6-74.1% and 95.2-99.0%, respectively, showing a slightly higher efficiency as compared to the ELISA performed using 6,6'-dimycoloyl trehalose from Mycobacterium tuberculosis. No cross-reactivity was found with sera from Nocardia-infected individuals.     

Bicarbonate actions on flagellar and Ca2+ -channel responses: initial events in sperm activation

At mating, mammalian sperm are diluted in the male and female reproductive fluids, which brings contact with HCO(3)(-) and initiates several cellular responses. We have identified and studied two of the most rapid of these responses. Stop-motion imaging and flagellar waveform analysis show that for mouse epididymal sperm in vitro, the resting flagellar beat frequency is 2-3 Hz at 22-25 degrees C. Local perfusion with HCO(3)(-) produces a robust, reversible acceleration to 7 Hz or more. At 15 mM the action of HCO(3)(-) begins within 5 seconds and is near-maximal by 30 seconds. The half-times of response are 8.8+/-0.2 seconds at 15 mM HCO(3)(-) and 17.5+/-0.4 seconds at 1 mM HCO(3)(-). Removal of external HCO(3)(-) allows a slow return to basal beat frequency over approximately 10 minutes. Increases in beat symmetry accompany the accelerating action of HCO(3)(-). As in our past work, HCO(3)(-) also facilitates opening of voltagegated Ca(2+) channels, increasing the depolarization-evoked rate of rise of intracellular Ca(2+) concentration by more than fivefold. This action also is detectable at 1 mM HCO(3)(-) and occurs with an apparent halftime of approximately 60 seconds at 15 mM HCO(3)(-). The dual actions of HCO(3)(-) respond similarly to pharmacological intervention. Thus, the phosphodiesterase inhibitor IBMX promotes the actions of HCO(3)(-) on flagellar and channel function, and the protein kinase A inhibitor H89 blocks these actions. In addition, a 30 minute incubation with 60 micro M cAMP acetoxylmethyl ester increases flagellar beat frequency to nearly 7 Hz and increases the evoked rates of rise of intracellular Ca(2+) concentration from 17+/-4 to 41+/-6 nM second(-1). However, treatment with several other analogs of cAMP produces only scant evidence of the expected mimicry or blockade of the actions of HCO(3)(-), perhaps as a consequence of limited permeation. Our findings indicate a requirement for cAMP-mediated protein phosphorylation in the enhancement of flagellar and channel functions that HCO(3)(-) produces during sperm activation.     

Recipient-induced transfer of the symbiotic plasmid pRL1JI in Rhizobium leguminosarum bv. viciae is regulated by a quorum-sensing relay

Analysis of the regulation of plasmid transfer genes on the symbiotic plasmid pRL1JI in Rhizobium leguminosarum bv. viciae has revealed a novel regulatory relay that is specifically poised to detect an N-acyl-homoserine lactone (AHL) made by different cells (potential recipients of pRL1JI). Adjacent to the traI-trbBCDEJKLFGHI plasmid transfer operon on pRL1JI are two regulatory genes, bisR and traR, which encode LuxR-type quorum-sensing regulators required for conjugation. Potential recipients of pRL1JI induce the traI-trb operon and plasmid transfer via a quorum-sensing relay involving BisR, TraR and the traI-trb operon in donor cells. BisR induces expression of traR in response to N-(3-hydroxy-7-cis-tetradecenoyl)-l-homoserine lactone (3-OH-C14:1-HSL), which is produced by CinI in potential recipient strains. In donor strains (carrying pRL1JI), BisR represses the expression of the chromosomal gene cinI; this repression results in a very low level of formation of 3-OH-C14:1-HSL and hence relatively low levels of expression of traR and the traI-trb operon in strains carrying pRL1JI. However, if 3-OH-C14:1-HSL from potential recipients is present, then traR and plasmid transfer are induced. The induction of traR occurs at very low concentrations of 3-OH-C14:1-HSL (around 1 nm). TraR then induces the traI-trb operon in a quorum-sensing dependent manner in re-sponse to the TraI-made AHLs, N-(3-oxo-octanoyl)-l-homoserine lactone and N-(octanoyl)-l-homoserine lactone. The resulting autoinduction results in high levels of expression of the traI-trb operon. Premature expression of the traI-trb operon is reduced by TraM, which probably titres out TraR preventing expression of traI when there are low levels of traR expression. Expression of traR in stationary phase cells is limited by feedback inhibition mediated by TraI-made AHLs.