Effects of thyroid hormone on the development of immune system in zebrafish

Effects of thyroxine (T4) and methimazole (MMI) on the development of the zebrafish immune system were investigated using continuous immersion treatment experiments. The effects of the treatments on thymus development were determined using computer-aided thymus morphometric analyses on in situ hybridization serial sections of the thymus while the effects on immune-related gene expression levels were monitored using quantitative real-time PCR. The findings indicate that thymus development and thymopoiesis, as indicated by thymus size, thymus Rag-1-positive region, and TCRAC expression level, were affected by T4 and MMI-treatments. With the exception of Ikaros, MMI-treated fish has lower immune-related gene expression levels, although it is not certain whether the effect resulted indirectly from the concomitant growth-retardation and/or directly from an effect on lymphopoiesis itself. The findings were comparable with those in mammalian system, thus providing the first evidence that the thyroid relationship with thymus development and lymphopoiesis is likely to be conserved from fish to higher vertebrates. It suggests the possibility of using zebrafish as a model system to investigate the molecular mechanisms involved in thyroid hormone-dependent disorders in the immune system.

Synthesis and evaluation of a new series of peptide-based endothelin receptor antagonists

Novel peptide-based endothelin (ET) receptor antagonists were designed and synthesized in our laboratory. BQ-485, HIM-CO-Leu-d-Trp-d-Trp-OH, was selected as the leading compound. The primary structures of these new tripeptides were ABO-CO-Leu-d-Trp-d-AA(X)-OH. The introduction of unnatural aromatic amino acids into these tripeptides was useful in the structure-activity relationship studies. Among the 20 tripeptides, 16 of them showed high activities against the contraction of rat aortic smooth muscles induced by ET-1.

Development and maturation of the immune system in zebrafish, Danio rerio: a gene expression profiling, in situ hybridization and immunological study

The development and maturation of the immune system in zebrafish was investigated using immune-related gene expression profiling by quantitative real-time polymerase chain reaction, in situ hybridization (ISH), immunoglobulin (Ig) detection by immuno-affinity purification and Western blotting as well as immersion immunization experiments. Ikaros expression was first detected at 1 day post-fertilization (dpf) and thereafter increased gradually to more than two-fold between 28 and 42dpf before decreasing to less than the initial 1dpf expression level in adult fish (aged 105dpf). Recombination activating gene-1 (Rag-1) expression levels increased rapidly (by 10-fold) between 3 and 17dpf, reaching a maximum between 21 and 28dpf before decreasing gradually. However, in adult fish aged 105dpf, the expression level of Rag-1 had dropped markedly, and was equivalent to the expression level at 3dpf. T-cell receptor alpha constant region and immunoglobulin light chain constant region (IgLC) isotype-1, 2 and 3 mRNAs were detected at low levels by 3dpf and their expression levels increased steadily to the adult range between 4 and 6 weeks post-fertilization (wpf). Using tissue-section ISH, Rag-1 expression was detected in head kidney by 2wpf while IgLC-1, 2 and 3 were detected in the head kidney and the thymus by 3wpf onwards. Secreted Ig was only detectable using immuno-affinity purification and Western blotting by 4wpf. Humoral response to T-independent antigen (formalin-killed Aeromonas hydrophila) and T-dependent antigen (human gamma globulin) was observed in zebrafish immunized at 4 and 6wpf, respectively, indicating that immunocompetence was achieved. The findings reveal that the zebrafish immune system is morphologically and functionally mature by 4-6wpf.

[Differences in haemozoin production and pathogenicity between chloroquine-sensitive and chloroquine-resistant strains of Plasmodium berghei]

AIM

To better understand the differences in haemozoin formation and pathogenicity between chloroquine-sensitive(N) and chloroquine-resistant(RC) strains of Plasmodium berghei.

METHODS

IRC mice were grouped as follows: group Xba I (Normal control, NC), group II (control treated with chloroquine alone, CC), group III (mice infected with N strain), group IV (mice infected with RC strain, RC) and group V (mice infected with RC strain and treated with chloroquine, RCC). Morphologic features of the parasites, parasitaemia, histological and ultrastructural changes of livers among the groups were compared.

RESULTS

Severe damages of the hepatic cells of the N group including increased lysosomes and swollen and fused mitochondria were detected. On the contrary, the prominent features in liver section of the RC group were inflammatory cell (notably mononuclear) infiltration and Kupffer cell activation. Numerous trophozoites and schizonts were sequestrated in hepatic sinusoids and less degeneration of parenchymal cells was found except for some swollen and vacuolated mitochondria. Internal food vacuoles containing haemozoin were found in the parasites of the N group, whereas external food vacuoles without haemozoin granules were arranged in foamy appearance within the parasitized cell of the RC group.

CONCLUSION

P. berghei RC strain may modify the mode of ingestion and degradation of hemoglobin in the parasites, resulting in impeding haemozoin formation. The difference in virulence between the N and RC strain of P. berghei is probably attributed to the significant differences in the induction of immune response of the host.

Morphologic transformation of the thymus in developing zebrafish

The morphologic transformation of the developing zebrafish thymus from 1 week postfertilization (wpf) to 15 wpf is described. The thymus overall morphology changed from a small pouch-like shape at 1 wpf to a conical shape between 2 and 3 wpf before acquiring a more complex shape from 4 wpf onward. Rapid growth rate along the lateral axis at the region near the pharyngeal epithelium occurred between 1 and 2 wpf, whereas rapid growth rate along the dorsal-ventral axis occurred between 3 and 6 wpf. Expansion of thymocyte population beginning from 1 wpf became more evident by 2 to 3 wpf, as indicated by the apparent increase of different sizes of lymphocytes, recombination activating gene-1 (rag-1), and T-cell antigen receptor alpha chain constant region (TCRAC) -positive cells. Tissue section in situ hybridization (ISH) analysis with rag-1 probe reveals that cortex-medullary regionalization has begun between 1 and 2 wpf as rag-1 expression clearly demarcated the cortex, whereas the medulla was rag-1 negative. The presence of TCRAC-positive cells in the medulla by 2-3 wpf, suggests that the thymic selection processes had begun. The zebrafish thymus is morphologically mature by 3 wpf. Early signs of thymic involution were observed in zebrafish aged 15 wpf.

Green fluorescent protein (GFP) transgenic fish and their applications

The coupling of the GFP reporter system with the optical clarity of embryogenesis in model fish such as zebrafish and medaka is beginning to change the picture of transgenic fish study. Since the advent of first GFP transgenic fish in 1995, GFP transgenic fish technology have been quickly employed in many areas such as analyses of gene expression patterns and tissue/organ development, dissection of promoters/enhancers, cell lineage and axonal pathfinding, cellular localization of protein products, chimeric embryo and nuclear transplantation, cell sorting, etc. The GFP transgenic fish also have the potentials in analysis of upstream regulatory factors, mutagenesis screening and characterization, and promoter/enhancer trap. Our own studies indicate that GFP transgenic fish may become a new source of novel variety of ornamental fish. Efforts are also being made in our laboratory to turn GFP transgenic fish into biomonitoring organisms for surveillance of environmental pollution.

Modulation of abscisic acid signal transduction and biosynthesis by an Sm-like protein in Arabidopsis

The phytohormone abscisic acid (ABA) regulates plant growth and development as well as stress tolerance. The Arabidopsis sad1 (supersensitive to ABA and drought) mutation increases plant sensitivity to drought stress and ABA in seed germination, root growth, and the expression of some stress-responsive genes. sad1 plants are also defective in the positive feedback regulation of ABA biosynthesis genes by ABA and are impaired in drought stress induction of ABA biosynthesis. SAD1 encodes a polypeptide similar to multifunctional Sm-like snRNP proteins that are required for mRNA splicing, export, and degradation. These results suggest a critical role for mRNA metabolism in the control of ABA signaling as well as in the regulation of ABA homeostasis.

[Effects of glutamine on the intestinal failure in rats model of acute necrotizing pancreatitis]

OBJECTIVE

To determine the effects of glutamine (Gln) on the intestinal failure in rats with acute necrotizing pancreatitis (ANP) and its possible mechanisms.

METHODS

Fifty-four Sprague-Dawley rats were randomly divided into 3 groups: sham operation (SO, n = 18), ANP (n = 18), and ANP treated with Gln (ANP + Gln, n = 18). ANP model was induced by injection of 5% sodium taurocholate solution into bilo-pancreatic duct. The therapy was continuously given with amino acid solution by a mini-pump via a central intravenous line. In addition, the ANP + Gin group was received 3% Gln dipeptide solution (equal to 2% Gln) with a dosage of 0.5g x kg(-1) x d(-1). These groups were isocaloric and isonitrogenous. Bacterial cultures from pancreas, mesenteric lymph node (MLN), liver, spleen and ascites were done at 24, 48, 72 h after operation. Endotoxin level in portal vein was determined. Pathologic changes of intestinal mucosa were also studied. Apoptosis of intestinal mucosa was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Expressions of insulin-like growth factor 1 (IGF-1), Gln synthetase (GSase) and glutaminase (Glnase) mRNA were assayed by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

At 24, 48, 72h, the positive rate of bacterial culture and the endotoxin concentration were increased significantly in ANP group compared to the SO group (P < 0.05), while Gln could decrease them significantly. Pathologic study showed that the height of mucosal villous in ANP group was lower than that in SO group, indicating the intestinal mucosa became more atrophy. However, the height of mucosal villous in ANP + Gln group was no significantly difference compared to that in SO group, indicated Gln could preserve the mucosa well. Apoptotic index was increased in ANP group and decreased in Gln treated rats. Expressions of IGF-1, GSase, Glnase mRNA were down-regulated in ANP group, but were up-regulated in ANP + Gln group.

CONCLUSIONS

The intestinal barrier function was impaired in ANP. Gln could protect intestinal barrier function. This action was probably related to its enhancement of IGF-1, GSase and Glnase mRNA expressions and its inhibition of intestinal mucosal apoptosis.

Differential expression of two cytochrome P450s involved in the biosynthesis of flavones and anthocyanins in chemo-varietal forms of Perilla frutescens

In Perilla frutescens, there are two varietal forms of anthocyanin accumulation, i.e. red and green forms. The cDNA clones encoding flavone synthase II (FSII) and flavonoid 3'-hydroxylase (F3'H), two cytochrome P450s that are involved in the biosynthesis of flavones and anthocyanins, were isolated from P. frutescens. The FSII cDNA encoded a 57.1 kDa protein designated as CYP93B6, and the F3'H cDNA encoded 57.5 kDa protein designated as CYP75B4. Recombinant CYP93B6 expressed in yeast converted flavanones to flavones with K(m) values of 8.8-11.9 microM. Recombinant CYP75B4 catalyzed 3'-hydroxylation of flavanones to the corresponding compounds with K(m) values of 18-20 microM. The CYP93B6 transcript accumulated to an equal level in leaves of both red and green forms of P. frutescens, in agreement with the accumulation pattern of flavones in the leaves. However, the CYP75B4 transcript was predominantly expressed in the red form of P. frutescens, and its expression was induced by light in conjunction with other transcripts of biosynthetic enzymes of anthocyanin. These results indicate that gene expression of a set of anthocyanin biosynthetic enzymes including F3'H is regulated coordinately only in the red form of P. frutescens but not in the green form, whilst FSII gene expression is controlled in a similar manner in red and green forms of P. frutescens.

Expression pattern of two zebrafish genes, cxcr4a and cxcr4b

We cloned and mapped two novel zebrafish genes, cxcr4a and cxcr4b, which are closely related to mammalian CXCR4. Expression analysis by reverse transcription-polymerase chain reaction and in situ hybridization demonstrated that these two genes are expressed in most cell lineages known to express Cxcr4 in mammals. These genes are co-expressed in lateral mesoderm and posterior midbrain. The transcripts of cxcr4a were detected in interneurons and endoderm, whereas cxcr4b was specifically expressed in sensory neurons, motoneurons and cerebellum. In the lateral mesoderm, cxcr4b transcripts appeared earlier than those of cxcr4a. Thus, the function of mammalian CXCR4 could be split between the two zebrafish genes. These genes probably derived from the genome duplication event, which occurred during the evolution of teleosts. Similar pairs of Cxcr4 may exist in other species, where genome duplication has occurred.

Bone marrow triglyceride accumulation and hormonal changes during long-term alcohol intake in male and female rats

BACKGROUND

Chronic alcohol consumption may influence the metabolism of adipocytes, the most abundant stromal cell phenotype in bone marrow, and promote bone marrow triglyceride accretion.

METHODS

Male and female rats 35 days old were fed the Lieber-De Carli liquid diet containing 36% of the calories as alcohol and were compared with pair-fed rats given an isocaloric liquid diet in which maltose-dextrin substituted for the calories supplied by alcohol. Other control rats were fed chow ad libitum. The rats were maintained on these diets for 64 days, after which the femurs were recovered and examined.

RESULTS

End weights of male and female alcohol-fed rats were significantly lower than both control groups. Femur diaphyseal bone marrow triglyceride levels were significantly increased in alcohol-fed male and female rats compared with both control groups. Femur bone marrow cavity diameters were significantly increased and cortical thickness was significantly decreased by alcohol in both males and females. Serum insulin levels were significantly decreased by alcohol only in female rats compared with the ad libitum but not the pair-fed control group, and insulin-like growth factor-1 levels were significantly reduced in male and female rats given the alcohol diet compared with both controls. Male testosterone and female estradiol levels remained unchanged. Male estradiol levels were significantly increased by alcohol compared with both controls, and female progesterone levels were significantly reduced by alcohol compared with pair-fed rats. Whereas female leptin levels were unchanged by alcohol, male leptin levels were significantly increased by alcohol compared with pair-fed rats.

CONCLUSIONS

Hormonal and growth factor changes during chronic alcohol consumption accompany triglyceride accumulation in diaphyseal bone marrow and may parallel the effects of alcohol on mesenchymal stem cells and the balance between osteogenic and adipogenic lineages and their cellular progenies.

A novel zebrafish bHLH gene, neurogenin3, is expressed in the hypothalamus

Many basic helix-loop-helix transcriptional factors play important roles in vertebrate neurogenesis. Among them, Neurogenins act as determination factors and initiate the expression of differentiation genes such as neuroD and other neurogenic genes. Here we describe a zebrafish cDNA (neurogenin3 or ngn3) encoding a novel member of the Neurogenin family closest to mouse Ngn3 and human NGN3. Using a zebrafish radiation hybrid panel, ngn3 was mapped to zebrafish linkage group 13 and the region displayed a conserved synteny with the region of human chromosome 10 containing NGN3. As judged by RT-PCR and whole-mount in situ hybridization, ngn3 expression in zebrafish started much later than other neurogenin genes, at only around 24 h post-fertilization (hpf) and with a higher level of expression on the left side of the anterio-ventral diencephalon. Later at 48 hpf, ngn3 expression was detected in a small number of cells in the tuberal hypothalamus. Unlike Ngn3 in the mouse, zebrafish ngn3 mRNAs were not detected in developing pancreas and spinal cord. Genomic Southern blot hybridization suggested that a closely related sequence is present in the zebrafish genome and the hypothetical gene might result from the recent genome duplication in certain teleost lineage and share the function of the common ancestor with the currently characterized ngn3.

[Bioslurry remediation of soil contaminated with polycyclic aromatic hydrocarbons]

Through the operation of the pilot-scale slurry reactor, the operational parameters of bioslurry remediation for soil contaminated with polycyclic aromatic hydrocarbons(PAHs), including temperature, ratio of water to soil, aeration flux, were determined. As the operational condition was that the ratio of water to soil was 2:1, the temperature was 20 degrees C-25 degrees C and aeration flux was 60 L/h, a good result of the remediation could be achieved. With the fungi isolated from contaminated soil as pure culture to degrade PAHs, after 34 days incubation, 90% of pyrene and 33.3% of benz[a]anthracene were degraded by Fusarium, 81.5% of pyrene and 49.2% of benz[a]anthracene were degraded by Mucor, 52% of pyrene and of 46% of benz[a]anthracene were degraded by Penicillium.

[Indexing system and its quantitative expression for soil quality evaluation in Hainan Island]

Based on the SOTER database and some FAO frameworks, a soil quality indexing system was established, and some evaluation results were presented for some selected GIS photo spot of tropical cropland in Hainan island. With connection to the spatial database, this system could perform the output of evaluation results. The performance and evaluation results were approved by the local expertise. It is suggested that the established models should be modified by the local practice.

[Degradation of phenanthrene and pyrene in contaminated soil by immobilized Zoogloea sp. and Fusarium sp]

Immobilized with PVA, sodium alginate and activated carbon, both Zoogloea sp. and Fusarium sp. strains could degrade phenanthrene and pyrene efficiently. The optimal carrier was made of 100 rho.g-1 L PVA, 5 sodium alginate rho.g-1 L and 50 activated carbon rho.g-1 L. The degradation rates of phenanthrene and pyrene in 10 days were 87.48% and 75.34% by the immobilized bacterium, 37.04% and 20.85% higher than those by the free bacterium, and the rates in 15 days were 84.36% and 74.87% by the immobilized fungus, 5.35% and 11.23% higher than those by the free fungus.

Expression of two novel zebrafish iroquois homologues (ziro1 and ziro5) during early development of axial structures and central nervous system

Previously, we reported a zebrafish iroquois gene, ziro3, and its expression during early embryogenesis (Mech. Dev. 87 (1999) 165). In the present study, we have isolated two novel zebrafish iroquois genes, ziro1 and ziro5, homologs of mouse Irx1 and mouse Irx5, respectively. The expression of both genes is initiated in dorsal neuroectoderm and mesoderm during gastrulation. Later, their expression appears in the central nervous system (CNS), excluding the telencephalon and most of the diencephalon. ziro1 expression is complementary to that of ziro3 in the notochord and later in the gut. In contrast, ziro5 expression mostly overlaps with that of ziro3. Interestingly, all three iroquois zebrafish genes are expressed in the notochord while only Irx3 is active in the mouse notochord. Their expression in later stages of embryogenesis was also compared.

[Cyclin-dependent kinase 4 inhibitor a and tumor]

INK4a/ARF locus encodes at least two products, P16(INK4a) and P19(ARF), which are very important in controlling cell-cycle arrest and apoptosis. Many human cancers have been found to be highly related to the mutations at this locus. Here is a review of its structure, function and role in tumor suppression.

[Co-metabolic degradation of pyrene in soil]

High molecular weight Polycyclic Aromatic Hydrocarbons (PAHs) are always degraded by means of co-metabolism. This study compared the degradation process of pyrene as sole source of carbon and energy and co-metabolic degradation process of pyrene. The degradation rate of pyrene after 25 days in the first process was 57%, while the degradation rate of pyrene in the co-metabolic processes were about 80%. The half-life of pyrene in the co-metabolic process was shorter than those in the processes without co-metabolism. Salicylic acid, phthalic acid, sodium succinate could serve as co-metabolic substrate to enhance the degradation rate of pyrene, and sodium succinate has the best effect. There was co-metabolic relationship between pyrene and phenanthrene which was a kind of low molecular weight PAHs, phenanthrene accelerated the degradation of pyrene, while naphthalene didn't. The principle of the co-metabolism and the optimal material used as co-metabolic substrate were demonstrated in this paper.

Effects and mechanisms of somatostatin analogs on apoptosis of pancreatic acinar cells in acute pancreatitis in mice

AIM

To investigate the effects of somatostatin analogs (SSa) on apoptosis of pancreatic acinar cells and apoptosis-regulated gene bax, and p53 in treating acute pancreatitis in mice.

METHODS

In cerulein-induced pancreatitis, with or without treatment of somatostatin, analogs (Octreotide) in CD-1 (BALB/c x DBetaAlpha/1) mice, apoptosis of pancreatic acinar cells was detected by using the TdT-mediated dUTP nick-end labeling (TUNEL) method, and the expression of apoptosis-regulated gene bax and p53 was determined by using the streptavidin-peroxidase immunohistochemical technique and the RT-PCR method, respectively.

RESULTS

On HE staining, acinar cells in the pancreas showed pyknotic nuclei and the formation of apoptotic bodies, which are the typical morphological features of apoptosis. Regarding TUNEL use, the apoptotic index of pancreatic acinar cells in the non-treated group at 5 and 14 h after induction of acute pancreatitis was significantly lower than those of the SSa-treated group, respectively (P < 0.01). On immunohistochemistry and RT-PCR, there was an expression of neither bax nor p53 in normal pancreatic tissues. The expression of bax in the SSa-treated group at 5 and 14 h after treatment of SSa was markedly higher than those of the non-treated group, respectively (P < 0.01), but there was no significant difference in the expression of p53 between the SSa-treated group and the non-treated group.

CONCLUSIONS

The induction of apoptosis in pancreatic acinar cells injury to reduce inflammatory reaction might be one of the mechanisms of SSa in treating acute pancreatitis in mice, and the mechanisms of apoptosis probably correlated with the expression of apoptosis-regulated gene bax, but have no relationship with the expression of p53.

Involving AP-2 transcription factor in connexin 26 up-regulation during pregnancy and lactation

Gap junction connexin 26 (Cx26) is up-regulated in mammary epithelial cells during pregnancy and lactation. To understand the transcriptional regulation of Cx26, we identified a protected DNase I footprint region (-140 to -113) in the rat Cx26 promoter. This rCx26 Promoter Footprinting Region, or CPFR, contains an Sp binding site (CCGCCC) overlapping with an AP-2 binding site (GCCCGCGGC), and is evolutionarily conserved. Nuclear extracts from rat mammary glands and human MCF-10 mammary epithelial cells formed protein-DNA complexes with the labeled CPFR probe in the electrophoretic mobility shift assay (EMSA), and these complexes were markedly enhanced during pregnancy and lactation. Antibody supershift analysis further identified the presence of Sp1, Sp3, and AP-2 in these binding complexes. Human mammary epithelial MCF-10A and MCF-12A cells were transiently transfected with chimeric mutant rCx26 promoter/luciferase reporter constructs, and luciferase activities measured. Mutations along the CPFR fragment drastically reduced the promoter activity, specially at the Sp/AP-2 overlapping site. Cotransfection of AP-2 with rCx26 promoter/reporter constructs into MCF-10 cells markedly induced the reporter activity. These data infer that AP-2, along with previously reported Sp transcription factors, is involved in the up-regulation of Cx26 gene during pregnancy and lactation.

Effects of recombinant human basic fibroblast growth factor on cell proliferation during mandibular fracture healing in rabbits

OBJECTIVE

To investigate the effects of recombinant human basic fibroblast growth factor (rhbFGF) on the cell proliferation during mandibular fracture healing in rabbits.

METHODS

The complex of rhbFGF and bovine type I collagen was implanted into the mandibular fracture site under periosteum of the animal. The whole mandible was harvested at 7, 14, 28, 56 and 84 days respectively after operation. The expression of proliferating cell nuclear antigen (PCNA) in callus was examined with immunohistochemical staining.

RESULTS

PCNA-positive cells in callus in the rhbFGF-treated group on days 7 and 14 were more than that in the control group (P<0.01).

CONCLUSIONS

It indicates that rhbFGF can stimulate cell proliferation during mandibular fracture healing in rabbits.

Genes that are uniquely stress regulated in salt overly sensitive (sos) mutants

Repetitive rounds of differential subtraction screening, followed by nucleotide sequence determination and northern-blot analysis, identified 84 salt-regulated (160 mM NaCl for 4 h) genes in Arabidopsis wild-type (Col-0 gl1) seedlings. Probes corresponding to these 84 genes and ACP1, RD22BP1, MYB2, STZ, and PAL were included in an analysis of salt responsive gene expression profiles in gl1 and the salt-hypersensitive mutant sos3. Six of 89 genes were expressed differentially in wild-type and sos3 seedlings; steady-state mRNA abundance of five genes (AD06C08/unknown, AD05E05/vegetative storage protein 2 [VSP2], AD05B11/S-adenosyl-L-Met:salicylic acid carboxyl methyltransferase [SAMT], AD03D05/cold regulated 6.6/inducible2 [COR6.6/KIN2], and salt tolerance zinc finger [STZ]) was induced and the abundance of one gene (AD05C10/circadian rhythm-RNA binding1 [CCR1]) was reduced in wild-type plants after salt treatment. The expression of CCR1, SAMT, COR6.6/KIN2, and STZ was higher in sos3 than in wild type, and VSP2 and AD06C08/unknown was lower in the mutant. Salt-induced expression of VSP2 in sos1 was similar to wild type, and AD06C08/unknown, CCR1, SAMT, COR6.6/KIN2, and STZ were similar to sos3. VSP2 is regulated presumably by SOS2/3 independent of SOS1, whereas the expression of the others is SOS1 dependent. AD06C08/unknown and VSP2 are postulated to be effectors of salt tolerance whereas CCR1, SAMT, COR6.6/KIN2, and STZ are determinants that must be negatively regulated during salt adaptation. The pivotal function of the SOS signal pathway to mediate ion homeostasis and salt tolerance implicates AD06C08/unknown, VSP2, SAMT, 6.6/KIN2, STZ, and CCR1 as determinates that are involved in salt adaptation.

The Arabidopsis HOS1 gene negatively regulates cold signal transduction and encodes a RING finger protein that displays cold-regulated nucleo--cytoplasmic partitioning

Low temperature is one of the most important environmental stimuli that control gene transcription programs and development in plants. In Arabidopsis thaliana, the HOS1 locus is a key negative regulator of low temperature-responsive gene transcription. The recessive hos1 mutation causes enhanced induction of the CBF transcription factors by low temperature as well as of their downstream cold-responsive genes. The hos1 mutant plants flower early, and this correlates with a low level of Flowering Locus C gene expression. The HOS1 gene was isolated through positional cloning. HOS1 encodes a novel protein with a RING finger motif near the amino terminus. HOS1 is ubiquitously expressed in all plant tissues. HOS1--GFP translational fusion studies reveal that HOS1 protein resides in the cytoplasm at normal growth temperatures. However, in response to low temperature treatments, HOS1 accumulates in the nucleus. Ectopic expression of HOS1 in wild-type plants causes cosuppression of HOS1 expression and mimics the hos1 mutant phenotypes.