Epigenetic Functions of Smchd1 Repress Gene Clusters on the Inactive X Chromosome and on Autosomes

The Smchd1 gene encodes a large protein with homology to the SMC family of proteins involved in chromosome condensation and cohesion. Previous studies have found that Smchd1 has an important role in CpG island (CGI) methylation on the inactive X chromosome (Xi) and in stable silencing of some Xi genes. In this study, using genome-wide expression analysis, we showed that Smchd1 is required for the silencing of around 10% of the genes on Xi, apparently independent of CGI hypomethylation, and, moreover, that these genes nonrandomly occur in clusters. Additionally, we found that Smchd1 is required for CpG island methylation and silencing at a cluster of four imprinted genes in the Prader-Willi syndrome (PWS) locus on chromosome 7 and genes from the protocadherin-alpha and -beta clusters. All of the affected autosomal loci display developmentally regulated brain-specific methylation patterns which are lost in Smchd1 homozygous mutants. We discuss the implications of these findings for understanding the function of Smchd1 in epigenetic regulation of gene expression.     

Intratracheal adenoviral-mediated delivery of iNOS decreases pulmonary vasoconstrictor responses in rats.

We hypothesized that adenovirus-mediated inducible nitric oxide synthase (iNOS) gene transduction of the lung would result in time-dependent iNOS overexpression and attenuate the vascular constrictor responses to a thromboxane mimetic, U-46619. Rats were treated via the trachea with surfactant alone (sham), surfactant containing an adenoviral construct with a cytomegalovirus promoter-regulated human iNOS gene (Adeno-iNOS), or an adenoviral construct without a gene insert (Adeno-Control). Adeno-iNOS-transduced rats demonstrated human iNOS mRNA and increased iNOS protein levels only in the lungs. Immunohistochemistry of lungs from Adeno-iNOS-treated animals demonstrated transgene expression in alveolar wall cells. In the lungs from Adeno-iNOS-transduced rats, the expression of iNOS protein and exhaled nitric oxide concentrations were increased on days 1-4 and 7 but returned to baseline values by day 14. The administration of the selective iNOS inhibitor L-N6-(1-iminoethyl)lysine dihydrochloride (L-NIL) decreased exhaled nitric oxide concentrations to levels found in Adeno-Control-transduced lungs. In a second group of rats, the segmental vasoconstrictor responses to U-46619 were determined in isolated, perfused lungs 3 days after transduction. Lungs from rats transduced with Adeno-iNOS had reduced total, arterial, and venous vasoconstrictor responses to U-46619 compared with sham, Adeno-Control, and control groups. In a third set of experiments, the response to 400 nM U-46619 in the presence of 10 microM L-NIL was not different in the isolated lungs from Adeno-Control- and Adeno-iNOS-transduced rats. We conclude that adenovirus-mediated iNOS gene transduction of the lung results in time-dependent iNOS overexpression, which attenuates the vascular constrictor responses to the thromboxane mimetic U-46619.     

Pattern and frequency of nondisjunction in oocytes from the Djungarian hamster are determined by the stage of first meiotic spindle inhibition

In order to study the mechanisms of nondisjunction at meiosis I in oocytes gonadotropin-stimulated Djungarian hamsters were treated at two stages [4.5 and 6 h post human chorionic gonadotropin (HCG)] during the preovulatory period with 1000 mg/kg Carbendazim (MBC). The compound, known to bind fast but reversibly to mammalian tubulin, was chosen to investigate whether the stage at which spindle function is inhibited affects the pattern of nondisjunction. Ovulated oocytes were cytologically prepared and scored for hyperhaploidy, diploidy and presegregation. Application at an early spindle phase, 4.5 h post HCG, to females stimulated with a low gonadotropin dose [3 IU pregnant mares serum (PMS); 2 IU HCG] caused a high frequency of nondisjunction (40.6%) with a more or less nonspecific pattern of malsegregated bivalents. Treatment at a late stage of spindle function (6 h post HCG) resulted in a less frequent (22.5%) but highly preferential malsegregation of those A-D group bivalents thought earlier to be late segregators. On the other hand, oocytes from females primed with a high (10 IU PMS and HCG) gonadotropin dose, a treatment assumed to delay meiosis by approximately 1.5 h, responded to MBC treatment at the late stage (6 h) with a nonspecific pattern and a high frequency (71.2%) of nondisjunction. The latter result is comparable to that in which MBC was given at the early stage (4.5 h) and after a low gonadotropin dose. The high nondisjunction response additionally indicates that spindles in hypergonadotropic stimulated oocytes are more susceptible and/or that the concentration of the inhibitor is higher in such oocytes. Only few oocytes with presegregation (3.1%; 0.0%; 1.7%) and few diploid oocytes (3.3%; 1.5%; 3.2%) with complete inhibition of meiosis I were observed. We conclude, that in Djungarian hamsters (1) the segregation of bivalents at meiosis I is asynchronous with the large A-D bivalents segregating last, (2) the phase in which spindle function is inhibited determines the pattern of nondisjunction, and (3) the resumption of meiosis I — from dictyotene to metaphase II — does not follow a rigidly timed programme but depends on the conditions of follicular maturation.     

A predatory use of counterillumination by the squaloid shark, Isistius brasiliensis

A number of very unusual morphological and behavioral characteristics attributed to the cookie-cutter shark, Isistius brasiliensis, may be explained by a novel use of counterillumination. Specifically, it is proposed that a band of pigment, located beneath the jaw and bounded by ventrally directed bioluminescence, acts as a lure which mimics the search image of many upward-looking pelagic predators.     

Salinity effects on growth and carbon balance in Lycopersicon esculentum and L. pennellii

The effects of salinity on growth and carbon balance in the cultivated tomato Lycopersicon esculentum (L.) Mill. cv. VF 234 and in a wild, salt-tolerant relative, L. pennellii (Correll) D'Arcy accession Atico, were compared. The level of salinity that significantly reduced growth and affected morphology was lower for the cultivated than for the wild species.
Net CO₂ fixation, stomatal conductance and the specific activity of ribulose bisphosphate carboxylase (EC 4.1.1.39) were more decreased by salinity in the wild tomato than in the cultivated. In both species, the salinity-associated decrease in assimilation was related to a decrease in net photosynthesis and to carbon reallocation favoring heterotrophic organs.