Sex Determination in Caenorhabditis elegans

In Caenorhabditis elegans, the decision to develop as a hermaphrodite or male is controlled by a cascade of regulatory genes. These genes and other tissue-specific regulatory genes also control sexual fate in the hermaphrodite germline, which makes sperm first and then oocytes. In this review, we summarize the genetic and molecular characterization of these genes and speculate how they mutually interact to specify sexual fate.     

Cellular mechanisms of paired electrical stimulation in ferret ventricular myocardium: relationship between myocardial force and stimulus interval change

Summary The subcellular mechanisms of twitch-force potentiation with paired electrical stimulation was studied in ferret ventricular myocardium using the bioluminescent calcium indicator aequorin. It is demonstrated for the first time that interpolation of an extrasystole in a train of conditioned twitches results in a beat-to-beat change in [Ca²⁺]_i and force. Steady-state twitch force and Ca _i ²⁺ were increased with paired stimulation. Increased [Ca²⁺]₀ in the setting of paired stimulation resulted in an increase in the amplitude of the postextrasystole and associated Ca²⁺ transient. Verapamil, a Ca²⁺ channel antagonist, had the opposite effect of increased [Ca²⁺]₀. Postextrasystole potentiation was still present, but diminished in amplitude. These results indicate that postextrasystole potentiation is in part due to a verapamil-depletable store (Ca²⁺). Postextrasystole potentiation is therefore predominantly dependent on sarcoplasmic reticulum (SR) Ca²⁺ loading. Ryanodine, an alkaloid which induces Ca²⁺ leakage from the SR, abolished postextrasystole potentiation; however, in the presence of ryanodine the extrasystole was potentiated. Caffeine, a phosphodiesterase inhibitor which induces SR Ca²⁺ release and impairs uptake, also abolished postextrasystole potentiation. As with ryanodine there was resultant potentiation of the extrasystole. In the case of caffeine the calcium transient consisted of a second slow component associated with extrasystole twitch potentiation. The results are consistent with sarcolemmal Ca²⁺ influx playing a role in potentiation of the extrasystole in the presence of an impaired SR. These data indicate that transsarcolemmal Ca²⁺ influx in the presence of impaired intracellular Ca²⁺ buffering can directly activate the myofilaments in agreement with reports on human myocardium.Abbreviations C conditioned stimulus - ESI extrasystolic interval - L_max active tension - PES postextrasystole - PESI postextrasystolic interval - SR sarcoplasmic reticulum - T test stimulus     

Early gene interaction during prepupal expression of Drosophila arginine kinase

Arginine kinase displays a distinctive rise and fall in specific activity and specific protein levels during the prepupal stage of Drosophila development with maximal activity occurring at morphological stage P3. This developmentally regulated peak is under the influence of ecdysone. Altered doses of the major ecdysone-inducible “early” genes at cytological regions 75B and 2B5 alter this pattern of expression while altered doses of another major “early” gene at 74EF have no effect. We hypothesize that a product of the 2B5 locus and a product of the 75B locus interact to effect this developmental pattern of expression of Drosophila arginine kinase. © 1992 Wiley-Liss, Inc.     

EVIDENCE FOR POLLINATION ECOTYPES IN THE YELLOW-FRINGED ORCHID,PLATANTHERA CILIARIS

Platanthera ciliaris is a butterfly-pollinated, terrestrial orchid with a loose terminal raceme of 10–50 orange flowers, characterized by a long nectariferous spur. In the southeastern United States, P. ciliaris occurs in the Appalachian mountains and coastal-plain physiographic provinces, but it is found rarely in the intervening Piedmont. In 1983 and 1984, detailed observations of two populations within these disjunct areas revealed that the butterfly species that serve as the primary pollinators differ sharply. In the mountains, Papilio troilus (spicebush swallowtail) was the most frequent and effective visitor, whereas in the coastal plain, P. palamedes (palamedes swallowtail) was the predominant pollinator. Proboscis lengths of P. troilus (mean = 23.3 mm) were significantly shorter than those of P. palamedes (mean = 28.7 mm). Floral characters, most notably spur length, also differed significantly between mountain (mean = 23.8 mm) and coastal-plain (mean = 25.6 mm) plants. In both 1983 and 1984, levels of pollinator service, as assessed by rates of removal and insertion of pollinia, were higher in the mountains (0.81 and 0.86) than in the coastal plain (0.63 and 0.67). In addition, fruit-set was significantly greater in mountain (83.9% in 1983, 86.5% in 1984) than in coastal-plain (63.8% in 1983, 65.5% in 1984) populations. We hypothesize that selection pressure exerted through pollinator proboscis lengths has resulted in pollination ecotypes of P. ciliaris. The short-spurred mountain plants appear to be in equilibrium with their short-tongued butterfly pollinators, receiving high levels of effective pollination and achieving high levels of fruit-set. Coastal-plain plants produce flowers with longer spurs which, nevertheless, are shorter than optimal for insuring that very long-tongued butterflies make contact with their pollinia. Thus, effective pollinator service and fruit-set are reduced. Correlation analyses in 1984 showed a positive relationship between spur length and fruit-set only in the coastal plain. The presence of long-tongued nectar thieves in the coastal plain may also contribute to lower effective pollinator service and fruit-set. Results of reciprocal-transplant studies attempting to determine the genetic basis of floral characters, including spur length, were inconclusive but suggest that differences between mountain and coastal-plain plants are not due solely to phenotypic plasticity.     

The hypolimnetic protozoan plankton of a eutrophic lake

The seasonal distribution of benthic species in the water column above and below the thermocline in a small eutrophic lake is described. During summer stratification populations of Spirostomum spp, Loxodes spp., Plagiopyla and Deltopylum become established in the plankton on or below the oxycline/thermocline. At shallow sites no migration occurred and populations of the migratory species in the benthos were sparse, with the exception of Plagiopyla which occurred in high densities in the sediment. Two distinct planktonic populations are established during stratification: an epilimnetic community of obligate planktonic ciliates and a hypolimnetic community of benthic migrants.     

Linear and circular dichroism of membranes from Rhodopseudomonas capsulata

Absorption, linear dichroism and circular dichroism spectra of Rhodopseudomonas capsulata (wild-type-St. Louis strain, mutant Y5 and mutant Ala⁺) are particularly sensitive to the nature of the light-harvesting bacteriochlorophyll-carotenoid-protein complexes. Evidence for exciton-type interactions is seen near 855 nm in the membranes from the wild-type and from mutant Y5, as well as in an isolated B-800 + 850 light-harvesting complex from mutant Y5. The strong circular dichroism that reflects these interactions is attenuated more than 10-fold in membranes from the Ala⁺ mutant, which lacks both B-800 + 850 and colored carotenoids and contains only the B-875 light-harvesting complex. These results lead to the conclusion that these two light-harvesting complexes have significantly different chromophore arrangements or local environments.     

The relationship between the size of mitochondria and the intensity of light that they scatter in different energetic states

The intensity of light scattered at 90° to the incident beam and the effective hydrodynamic radii of mitochondria incubated under a variety of conditions have been measured. Addition of high concentrations of uncouplers to respiring mitochondria resulted in a decrease in scatter which was not due to swelling. Addition of valinomycin to mitochondria depleted of substrate in K⁺-free medium produced an increase in scatter that was not due to shrinking. It is concluded that changes in the intensity of scattered light are not reliable indices of changes of volume of mitochondria, and that changes in conformation with changes in metabolic state dominate changes in light scatter. A molecular mechanism for the effect of metabolic state upon the scattered intensity is suggested.     

Tyrosine aminotransferase deficiency in mink (Mustela vision): A model for human tyrosinemia II

Mink pseudodistemper, a recessive disease associated with high blood tyrosinelevels, is an animal analogue of the human inborn error of metabolism, tyrosinemia II. Affected mink and man have eye and skin lesions. Affected mink have no hepatic tyrosine aminotransferase (TAT) activity, as measured immunologically and biochemically. Hepatic mitochondrial aspartate aminotransferase is increased to 188% of control. This new genetic animal model of TAT deficiency should allow new studies of tyrosine metabolism.Supported by NIH Grants AM-17253 (LAG), 5T32-AM-07093 (LAG), and RCDA AM-0008 (LAG), grants from the Wisconsin State Mink Advisory Board, and a BRSG grant for the Graduate School of the University of Wisconsin, Madison, Publication No. 82 of the dermatology research laboratories of Duke University Medical Center.     

Role of collagen and fibronectin in neural crest cell adhesion and migration

Cultured neural crest cells which are freshly trypsinized require serum or purified fibronectin to attach to collagen substrates of types I–V. Furthermore, neural crest cells migrate in a Boyden chamber in response to fibronectin, and a “checkerboard” analysis demonstrates that fibronectin is both chemotactic and chemokinetic for these cells. It is proposed that collagen serves as a substrate for neural crest cells as they migrate in the early embryo. By mediating the cells' attachment to collagen, fibronectin may influence the movement of the cells. Local differences in fibronectin concentration or availability in the matrix could affect the degree of attachment of the cells to the collagen substrate and could also direct their migration by serving as a chemoattractant.