Hybridization in the mexican and 13-lined ground squirrels,Spermophilus mexicanus andSpermophilus tridecemlineatus

Summary Evidence of hybridization between the ground squirrels,Spermophilus tridecemlineatus andS. mexicanus is presented on the basis of chromosomal and protein data. The hybrids produced appear to be completely interfertile. Based on the evidence of hybridization and the recent reestablishment of contact between these two species, they are considered to be semispecies.Supported by Faculty Research Grant No. 34925 from North Texas State University awarded toZimmerman.     

Gentic control of erythrocyte esterase (Es-1) in the pinon mouse,Peromyscus truei (Shufeldt)

Zusammenfassung Kreuzungsversuche und elektrophoretische Analyse der Erythrocytenesterase bei der MausPeromyscus truei zeigten, dass die Homozygoten je eine Enzymbande mit unterschiedlichen Beweglichkeiten aufweisen, während bei den Heterozygoten beide Enzymbanden vorkommen, was mit der Annahme der Abspaltung von zwei kodominanten Allelen eines einzigen autosomalen Locus übereinstimmt.

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Supported by Faculty Research Grant No. 35064 from North Texas State University awarded toZimmerman.     

Lethargus is a Caenorhabditis elegans sleep-like state

There are fundamental similarities between sleep in mammals and quiescence in the arthropod Drosophila melanogaster, suggesting that sleep-like states are evolutionarily ancient. The nematode Caenorhabditis elegans also has a quiescent behavioural state during a period called lethargus, which occurs before each of the four moults. Like sleep, lethargus maintains a constant temporal relationship with the expression of the C. elegans Period homologue LIN-42 (ref. 5). Here we show that quiescence associated with lethargus has the additional sleep-like properties of reversibility, reduced responsiveness and homeostasis. We identify the cGMP-dependent protein kinase (PKG) gene egl-4 as a regulator of sleep-like behaviour, and show that egl-4 functions in sensory neurons to promote the C. elegans sleep-like state. Conserved effects on sleep-like behaviour of homologous genes in C. elegans and Drosophila suggest a common genetic regulation of sleep-like states in arthropods and nematodes. Our results indicate that C. elegans is a suitable model system for the study of sleep regulation. The association of this C. elegans sleep-like state with developmental changes that occur with larval moults suggests that sleep may have evolved to allow for developmental changes.     

Cyclic GMP-sensitive conductance of retinal rods consists of aqueous pores

The surface membrane of retinal rod and cone outer segments contains a cation-selective conductance which is activated by 3',5'-cyclic guanosine monophosphate (cGMP). Reduction of this conductance by a light-induced decrease in the cytoplasmic concentration of cGMP appears to generate the electrical response to light, but little is known about the molecular nature of the conductance. The estimated unitary conductance is so small that ion transport might occur via either a carrier or a pore mechanism. Here we report recordings of cGMP-activated single-channel currents from excised rod outer segment patches bathed in solutions low in divalent cations. Two elementary conductances, of approximately 24 and 8 pS, were observed. These conductances are too large to be accounted for by carrier transport, indicating that the cGMP-activated conductance consists of aqueous pores. The dependence of the channel activation on the concentration of cGMP suggests that opening of the pore is triggered by cooperative binding of at least three cGMP molecules.     

Effects of forest fuel smoke on dwarf mistletoe seed germination

Seeds of three species of dwarf mistletoe, Arceuthobium americanum Nutt. Ex Engelm., A. cyanocarpum Coulter & Nelson, and A. vaginatum subsp. cryptopodum (Engelm.) Hawksw. & Wiens, were exposed to smoke from burning forest fuels. Premeasured amounts of coniferous needles and branch wood were burned in a small incinerator with smoke passing through a closed chamber containing the seeds. Following three different smoke treatments and one high-temperature treatment, tests were conducted to evaluate the effects of these treatments on seed germination. Germination was inhibited for all species when the seeds were exposed to smoke for 60 minutes or longer. Seeds of A. americanum were unaffected by exposures to smoke from drier fuels. The percentage of germinating seeds of A. cyanocarpum and A. vaginatum showed little effect from exposures of up to 30 minutes.     

Synthetic hosts by monomolecular imprinting inside dendrimers

Synthetic host systems capable of selectively binding guest molecules are of interest for applications ranging from separations and chemical or biological sensing to the development of biomedical materials. Such host systems can be efficiently prepared by 'imprinting' polymers or inorganic materials with template molecules, which, upon removal, leave behind spatially arranged functional groups that act as recognition sites. However, molecularly imprinted polymers have limitations, including incomplete template removal, broad guest affinities and selectivities, and slow mass transfer. An alternative strategy for moulding desired recognition sites uses combinatorial libraries of assemblies that are made of a relatively small number of molecules, interconverting in dynamic equilibrium; upon addition of a target molecule, the library equilibrium shifts towards the best hosts. Here we describe the dynamic imprinting of dendritic macromolecules with porphyrin templates to yield synthetic host molecules containing one binding site each. The process is based on our general strategy to prepare cored dendrimers, and involves covalent attachment of dendrons to a porphyrin core, cross-linking of the end-groups of the dendrons, and removal of the porphyrin template by hydrolysis. In contrast to more traditional polymer imprinting, our approach ensures nearly homogeneous binding sites and quantitative template removal. Moreover, the hosts are soluble in common organic solvents and amenable to the incorporation of other functional groups, which should facilitate further development of this system for novel applications.     

Differential expression of myc family genes during murine development

The myc family of cellular oncogenes contains three known members. The N-myc and c-myc genes have 5'-noncoding exons, strikingly homologous coding regions, and display similar oncogenic potential in an in vitro transformation assay. The L-myc gene is less well characterized, but shows homology to N-myc and c-myc (ref. 6; also see below). c-myc is expressed in most dividing cells, and deregulated expression of this gene has been implicated in the development of many classes of tumours. In contrast, expression of N-myc has been found only in a restricted set of tumours, most of which show neural characteristics; these include human neuroblastoma, retinoblastoma and small cell lung carcinoma (SCLC). L-myc expression has so far been found only in SCLC. Activated N-myc and L-myc expression has been implicated in oncogenesis; for example, although N-myc expression has been found in all neuroblastomas tested, activated (greatly increased) N-myc expression, resulting from gene amplification, is correlated with progression of the tumour. We now report that high-level expression of N- and L-myc is very restricted with respect to tissue and stage in the developing mouse, while that of c-myc is more generalized. Furthermore, we demonstrate that N-myc is not simply a neuroectoderm-specific gene; both N- and L-myc seem to be involved in the early stages of multiple differentiation pathways. Our findings suggest that differential myc gene expression has a role in mammalian development and that the normal expression patterns of these genes generally predict the types of tumours in which they are expressed or activated.