The circadian gene Clock is required for the correct early expression of the head specific gene Otx2

The circadian cycle is a universal molecular mechanism for imposing cyclical control on cellular processes. Here we have examined the role of one of the crucial circadian genes, Clock, in early Xenopus development. We show that a dominant negative version of Clock can block the function of the endogenous Clock gene. Doing so during early development reduces Otx2 expression in a highly specific manner and results in anterior defects. Together with previous work (Green et al. (2001) Mech. Dev. 105-110), these results suggest that a positive regulatory loop exists between Clock and Otx2.     

Developmental regulation of somatostatin gene expression in the brain is region specific

Developmental regulation of somatostatin (SRIF) gene expression was studied in five regions of rat brain and in rat stomach. Total RNA was isolated from hypothalamus, cortex, brainstem, cerebellum, and olfactory bulb, as well as stomach at eight stages of development from prenatal day 16 to postnatal day 82. Hybridization of a 32P-labeled rat SRIF cDNA probe to Northern blots of total RNA from the above tissues during development demonstrated a single hybridizing band approximately 670 base pairs in length. When SRIF mRNA levels from each stage of development were quantified and normalized by the amount of poly (A)+ RNA present at that stage of development, a unique pattern of SRIF gene expression was seen in each region. In brainstem and cerebellum, SRIF mRNA levels peaked early in development between prenatal day 21 and postnatal day 8 and then declined until postnatal day 82. Hypothalamus and cortex, on the other hand, showed a progressive increase during development with peak levels occurring between postnatal days 13 and 82. In contrast, stomach and olfactory bulb showed SRIF mRNA levels which were low during early development and which rose late in development (postnatal days 13 to 82). Marked differences in the amount of SRIF mRNA within each region were present as well. These data suggest that there is differential expression of the SRIF gene in different regions of the brain and in the stomach during development. Further study of this phenomenon may provide insight into the in vivo control of SRIF gene expression and the role of SRIF in the developing brain.     

The expression level determines the surface distribution of the transferrin receptor in Trypanosoma brucei

The transferrin receptor (TfR) of Trypanosoma brucei is a heterodimer attached to the surface membrane by a glycosylphosphatidylinositol (GPI) anchor. The TfR is restricted to the flagellar pocket, a deep invagination of the plasma membrane. The membrane of the flagellar pocket and the rest of the cell surface are continuous, and the mechanism that selectively retains the TfR in the pocket is unknown. Here, we report that the TfR is retained in the flagellar pocket by a specific and saturable mechanism. In bloodstream-form trypanosomes transfected with the TfR genes, TfR molecules escaped flagellar pocket retention and accumulated on the entire surface, even at modest (threefold) overproduction levels. Similar surface accumulation was observed when the TfR levels were physiologically upregulated threefold when trypanosomes were starved for transferrin. These results suggest that the TfR flagellar pocket retention mechanism is easily saturated and that control of the expression level is critical to maintain the restricted surface distribution of the receptor.     

Hemodilutional anemia is associated with increased cerebral neuronal nitric oxide synthase gene expression.

Severe hemodilutional anemia may reduce cerebral oxygen delivery, resulting in cerebral tissue hypoxia. Increased nitric oxide synthase (NOS) expression has been identified following cerebral hypoxia and may contribute to the compensatory increase in cerebral blood flow (CBF) observed after hypoxia and anemia. However, changes in cerebral NOS gene expression have not been reported after acute anemia. This study tests the hypothesis that acute hemodilutional anemia causes cerebral tissue hypoxia, triggering changes in cerebral NOS gene expression. Anesthetized rats underwent hemodilution when 30 ml/kg of blood were exchanged with pentastarch, resulting in a final hemoglobin concentration of 51.0 +/- 1.2 g/l (n = 7 rats). Caudate tissue oxygen tension (Pbr(O(2))) decreased transiently from 17.3 +/- 4.1 to 14.4 +/- 4.1 Torr (P < 0.05), before returning to baseline after approximately 20 min. An increase in CBF may have contributed to restoring Pbr(O(2)) by improving cerebral tissue oxygen delivery. An increase in neuronal NOS (nNOS) mRNA was detected by RT-PCR in the cerebral cortex of anemic rats after 3 h (P < 0.05, n = 5). A similar response was observed after exposure to hypoxia. By contrast, no increases in mRNA for endothelial NOS or interleukin-1beta were observed after anemia or hypoxia. Hemodilutional anemia caused an acute reduction in Pbr(O(2)) and an increase in cerebral cortical nNOS mRNA, supporting a role for nNOS in the physiological response to acute anemia.     

Ribosomal protein gene expression is cell type specific during development in Dictyostelium discoideum

Starvation for amino acids initiates the developmental cycle in the cellular slime mold, Dictyostelium discoideum. Upon starvation one of the earliest developmental events is the selective loss of the ribosomal protein mRNAs from polysomes. This loss depends upon sequences in the 5' non-translated leader of the ribosomal protein (r-protein) mRNAs. Here evidence is presented which indicates that those cells which will become prestalk cells express the ribosomal protein genes during development under starvation conditions. Cells which enter the prespore pathway shut off r-protein synthesis. The promoter and 5' non-translated leader sequences from two ribosomal protein genes, the rp-L11 and the rp-S9 genes, are fused to the Escherichia coli beta-galactosidase reporter gene. While beta-galactosidase enzyme activity is detected in situ in most growing cells, by 15 h of development beta-galactosidase enzyme activity is largely lost from the prespore cells although strong beta-galactosidase enzyme activity is present in the prestalk cells. These observations suggest the possibility that the ribosomal protein mRNAs are excluded from polysomes in a cell-type-specific manner.     

Mass mortality in Pacific oysters is associated with a specific gene expression signature

Mass mortality events occur in natural and cultured communities of bivalve molluscs. The Pacific oyster, Crassostrea gigas, is a dominant species in many intertidal locations as well as an important aquacultured bivalve species, and for the last 50 years, adult oysters have suffered frequent and extreme mass mortality events during summer months. To investigate the molecular changes that precede these mortality events, we employed a novel nonlethal sampling approach to collect haemolymph samples from individual oysters during the period that preceded a mortality event. Microarray-based gene expression screening of the collected haemolymph was used to identify a mortality gene expression signature that distinguished oysters that survived the mortality event from those individuals that died during the event. The signature was cross-validated by comparing two separate episodes of mortality. Here, we report that near-mortality oysters can be distinguished from longer-lived oysters by the elevated expression of genes associated with cell death, lysosomal proteolysis, and cellular assembly and organization. These results show the potential utility of nonlethal sampling approaches for investigating the environmental causes of mortality in natural populations in the field, and for predicting when such events could occur and which individuals will be affected.