Genetic analysis of sterile mutants in the dpy-5 unc-13 (I) genomic region of Caenorhabditis elegans

Essential genes were identified in the 1.5-map unit dpy-5 unc-13 region of chromosome I in the Caenorhabditis elegans genome by rescuing lethal mutations using the duplication sDp2. In this paper, we report the mapping and complementation testing of lethal mutations, 45 of which identify 18 new, essential genes. This analysis brings the number of essential genes defined by the sDp2 rescue of lethal mutants to 97; 64 of these map between dpy-5 and unc-13. 61% of these essential genes are identified by more than one allele. Positioning of the mutations was done using the breakpoints of six duplications. The mutant phenotypes of 14 loci essential for fertility were characterized by Nomarski microscopy and DAPI staining. None of the mutants were rescued by wild-type male sperm. The cytological data showed that four genes produced mutants with defects in gonadogenesis, let-395, let-603, let-605 and let-610. Mutations in seven genes, let-355, let-367, let-384, let-513, let-544, let-545 and let-606, affected germ cell proliferation or gametogenesis. Mutants for the remaining three genes, let-370, let-599 and let-604, produced eggs that failed to develop or hatch, thereby acting as maternal effect lethals. We observed a nonrandom distribution of arrest phenotypes with regard to map position. Received: 8 May 1996 / Accepted : 27 January 1997     

Electron paramagnetic resonance saturation studies of P-700+ reaction center chlorophyll in plant photosynthesis

Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T1, and spin-spin, T2, relaxation times of P-700+ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K less than or equal to T less than or equal to 100 K. T1 was 200 mus at 100 K and increased to 900 mus at 10 K. T2 was 40 ns at 40 K and increased to 100 ns at 10 K. T1 for 40 K less than or equal to T less than or equal to 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T1 deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T1 of P-700+ were examined: T1 of P-700+ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700+ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700+ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700+ due to either the iron sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700+ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of P-700+ signal. The absence of dipolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700+ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.     

Dapper Antagonist of Catenin-1 Cooperates with Dishevelled-1 during Postsynaptic Development in Mouse Forebrain GABAergic Interneurons

Synaptogenesis has been extensively studied along with dendritic spine development in glutamatergic pyramidal neurons, however synapse development in cortical interneurons, which are largely aspiny, is comparatively less well understood. Dact1, one of 3 paralogous Dact (Dapper/Frodo) family members in mammals, is a scaffold protein implicated in both the Wnt/β-catenin and the Wnt/Planar Cell Polarity pathways. We show here that Dact1 is expressed in immature cortical interneurons. Although Dact1 is first expressed in interneuron precursors during proliferative and migratory stages, constitutive Dact1 mutant mice have no major defects in numbers or migration of these neurons. However, cultured cortical interneurons derived from these mice have reduced numbers of excitatory synapses on their dendrites. We selectively eliminated Dact1 from mouse cortical interneurons using a conditional knock-out strategy with a Dlx-I12b enhancer-Cre allele, and thereby demonstrate a cell-autonomous role for Dact1 during postsynaptic development. Confirming this cell-autonomous role, we show that synapse numbers in Dact1 deficient cortical interneurons are rescued by virally-mediated re-expression of Dact1 specifically targeted to these cells. Synapse numbers in these neurons are also rescued by similarly targeted expression of the Dact1 binding partner Dishevelled-1, and partially rescued by expression of Disrupted in Schizophrenia-1, a synaptic protein genetically implicated in susceptibility to several major mental illnesses. In sum, our results support a novel cell-autonomous postsynaptic role for Dact1, in cooperation with Dishevelled-1 and possibly Disrupted in Schizophrenia-1, in the formation of synapses on cortical interneuron dendrites.     

Nucleic acid relationships among Acholeplasma species.

3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically.     

Iron-sulfur centers in the photosynthetic reaction center complex fromChlorobium vibrioforme. Differences from and similarities to the iron-sulfur centers in Photosystem I

The photosynthetic reaction center complex from the green sulfur bacteriumChlorobium vibrioforme has been isolated under anaerobic conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals polypeptides with apparent molecular masses of 80, 40, 30, 18, 15, and 9 kDa. The 80- and 18-kDa polypeptides are identified as the reaction center polypeptide and the secondary donor cytochromec ₅₅₁ encoded by thepscA andpscC genes, respectively. N-terminal amino acid sequences identify the 40-kDa polypeptide as the bacteriochlorophylla-protein of the baseplate (the Fenna-Matthews-Olson protein) and the 30-kDa polypeptide as the putative 2[4Fe-4S] protein encoded bypscB. Electron paramagnetic resonance (EPR) analysis shows the presence of an iron-sulfur cluster which is irreversibly photoreduced at 9K. Photoaccumulation at higher temperature shows the presence of an additional photoreduced cluster. The EPR spectra of the two iron-sulfur clusters resemble those of F_A and F_B of Photosystem I, but also show significantly differentg-values, lineshapes, and temperature and power dependencies. We suggest that the two centers are designated Center I (with calculatedg-values of 2.085, 1.898, 1.841), and Center II (with calculatedg-values of 2.083, 1.941, 1.878). The data suggest that Centers I and II are bound to thepscB polypeptide.