Biomedical subjects

P J Chen

Publications and source records attributed to P J Chen.

At least 19 recordsLinked to original sources

PubMed2006

Post-translational modification of delta antigen of hepatitis D virus.

The hepatitis delta virus (HDV) genome has only one open reading frame, which encodes the viral small delta antigen. After RNA editing, the same open reading frame is extended 19 amino acids at the carboxyl terminus and encodes the large delta antigen. These two viral proteins escort the HDV genome through different cellular compartments for the complicated phases of replication, transcription and, eventually, the formation of progeny virions. To orchestrate these events, the delta antigens have to take distinct cues to traffic to the right compartments and make correct molecular contacts. In eukaryotes, post-translational modification (PTM) is a major mechanism of dictating the multiple functions of a single protein. Multiple PTMs, including phosphorylation, isoprenylation, acetylation, and methylation, have been identified on hepatitis delta antigens. In this chapter we review these PTMs and discuss their functions in regulating and coordinating the life cycle of HDV.

Acetylation↗

PubMed2003

Improved early detection of cervical intraepithelial lesions by combination of conventional Pap smear and speculoscopy.

PURPOSE: To evaluate the efficacy of the addition of speculoscopy to a Pap smear in cervical cancer screening. METHODS: All women were screened using the Pap smear plus speculoscopy (PapSure) and colposcopy in the multicenter trial. The final diagnosis of each patient was based on a histological evaluation of the colposcopic target biopsy. Results were analyzed using a proportional compare test, sensitivity, specificity and predictive value with significant value determined at less than 0.05. RESULTS: Of 1,717 eligible cases, 26 cases had LGSIL and 16 cases had HGSIL. Of the Pap smears, five cases had LSIL and 14 cases had HGSIL. Of the combination of the PapSure, 23 cases had LGSIL and 16 cases had HGSIL. The sensitivity of the Pap smear to that of PapSure was calculated at 45.2% and 92.9%, respectively (p < 0.001). The estimated cost to detect a cervical lesion using PapSure is less than that of the Pap smear. CONCLUSION: The addition of speculoscopy along with a Pap smear screening results in early detection of cervical lesions in comparison to the Pap smear alone. This screening combination is also more cost-effective and requires fewer visits to the clinic in comparison to a Pap smear screening alone.

Adult↗

PubMed2001

Cell cycle analysis and detection of proliferative cell nuclear antigen of the endometrium after hormone replacement therapy.

BACKGROUND: To understand the effect of sequential combined hormone replacement therapy (HRT) on the postmenopausal endometrium. METHODS: Sonographic endometrial thickness, endometrial histopathology, flow cytometric cell cycle analysis and the level of proliferative cell nuclear antigen (PCNA) were studied. RESULTS: One hundred and thirty-eight postmenopausal women were enrolled in this study. Among which, 97 women had their endometrium being adequately obtained; the most frequent type of histopathology was normal endometrium (91.8%). Endometrial hyperplasia was found in seven patients (7.2%), including typical simple hyperplasia (n=1, 1%), focal simple hyperplasia (n=5, 5.2%) and complex hyperplasia without atypia (n=1, 1%). The proliferative fractions (PF; S plus G2-M phase) of cells from normal and hyperplastic endometrium of menopausal women after HRT were 8.18 and 8.95%, respectively, which were lower than those from 29 premenopausal women without HRT. The level of PCNA of normal and hyperplastic endometrium in postmenopausal women after HRT was about 80 and 84%, respectively, of that from premenopausal endometrium. CONCLUSIONS: Our study showed the PF of the cell cycle and the level of PCNA were not increased in the menopausal endometrium under HRT as compared to the premenopausal controls.

Aged↗

PubMed2001

Single nucleotide polymorphisms in intron 2 of the human interleukin-1 receptor antagonist (IL-1Ra) gene: further definition of the IL-1 beta and IL-1Ra polymorphisms in North American Caucasians and Taiwanese Chinese.

Previous studies have suggested that a variable number tandem repeat (VNTR) polymorphism in the second intron of the interleukin-1 receptor antagonist (IL-1Ra) gene and the single nucleotide polymorphisms at positions -511 and +3954 of the IL-1beta gene might be associated with increased risks of chronic inflammatory diseases, autoimmune diseases and gastric cancer. In the present study, IL-1beta and IL-1Ra genotypes were analyzed among Asians in Taiwan and Caucasians in North America. We identified a novel polymorphism with 3 nucleotide substitutions in the IL-1Ra VNTR 2-repeat allele. One of the substitutions corresponds with the fourth 3' end nucleotide of the reverse primer that is often used for analysis of the IL-1Ra-associated VNTR locus. Mismatching between this primer and the 2-repeat allele can cause misleading amplification results when stringent conditions are used for annealing. The estimated haplotype frequencies of the variant IL-1 genes were significantly different between Taiwanese and Caucasians. The frequency of the pro-inflammatory IL-1Ra 2-repeat allele was significantly lower in Taiwanese than in Caucasians. In contrast, the frequencies of the pro-inflammatory IL-1beta -511T allele and +3954C allele were significantly higher among Taiwanese compared with Caucasians.

Asian People↗

PubMed2001

Lamivudine treatment for hepatitis B reactivation in HBsAg carriers after organ transplantation: a 4-year experience.

BACKGROUND: Reactivation of hepatitis B after organ transplantation in hepatitis B surface antigen (HBsAg) carriers may be fatal. In this study, we reported our experience of lamivudine treatment in HBsAg carriers who had post-transplant reactivation of hepatitis B. METHODS: The patients were 15 men and one woman. Nine received kidney transplants, six received heart transplants, and one received a lung transplant. They developed a reactivation of hepatitis B 1-101 months (median, 14 months) after transplantation. They received lamivudine 100 mg daily on a compassionate-use basis, and had regular follow ups. The median pretreatment total serum bilirubin level was 3.0 mg/dL, and the alanine aminotransferase level was 357 U/L. Four of the 16 patients were positive for HBeAg. The serum hepatitis B virus (HBV) DNA levels were > 3000 pg/mL in 13 (81%) patients. Three were coinfected with hepatitis C virus. RESULTS: The overall survival rate was 75%. All four fatal cases had a pretreatment total serum bilirubin level of > or = 3 mg/dL. Serum HBV-DNA soon became undetectable in 12 survivors. Of the 12 survivors, after a median treatment period of 101 weeks, a lamivudine-resistant strain with variation in the YMDD motif of the HBV polymerase gene developed in three (25%). None had significant adverse reactions to lamivudine treatment. CONCLUSIONS: These results indicated that lamivudine is effective in the treatment of post-transplant hepatitis B reactivation, including patients with dual chronic hepatitis B and C. Early recognition of HBV reactivation and prompt lamivudine treatment are important to prevent mortality.

Adult↗

PubMed2001

A cGMP-dependent protein kinase is implicated in wild-type motility in C. elegans.

In mammals, cyclic GMP and cGMP-dependent protein kinases (cGKs) have been implicated in the regulation of many neuronal functions including long-term potentiation and long-term depression of synaptic efficacy. To develop Caenorhabditis elegans as a model system for studying the neuronal function of the cGKs, we cloned and characterized the cgk-1 gene. A combination of approaches showed that cgk-1 produces three transcripts, which differ in their first exon but are similar in length. Northern analysis of C. elegans RNA, performed with a probe designed to hybridize to all three transcripts, confirmed that a major 3.0 kb cgk-1 transcript is present at all stages of development. To determine if the CGK-1C protein was a cGMP-dependent protein kinase, CGK-1C was expressed in SF:9 cells and purified. CGK-1C shows a K(a) of 190 +/- 14 nM for cGMP and 18.4 +/- 2 microM for cAMP. Furthermore, CGK-1C undergoes autophosphorylation in a cGMP-dependent manner and is inhibited by the commonly used cGK inhibitor, KT5823. To determine which cells expressed CGK-1C, a 2.4-kb DNA fragment from the promoter of CGK-1C was used to drive GFP expression. The CGK-1C reporter construct is strongly expressed in the ventral nerve cord and in several other neurons as well as the marginal cells of the pharynx and intestine. Finally, RNA-mediated interference of CGK-1 resulted in movement defects in nematode larvae. These results provide the first demonstration that cGMP-dependent protein kinase is present in neurons of C. elegans and show that this kinase is required for normal motility.

Animals↗

PubMed2001

Chromosomal allelic imbalance evolving from liver cirrhosis to hepatocellular carcinoma.

BACKGROUND & AIMS: Cirrhotic nodules have long been assumed to be the precancerous lesions of hepatocellular carcinoma (HCC). We thus investigated the allelic imbalance (AI) in cirrhotic nodules to define the genetic aberrations in early hepatocarcinogenesis. METHODS: One hundred eighty cirrhotic nodules from 7 female patients with HCC were collected by microdissection. Their clonality nature was assessed by examining the X chromosome methylation pattern. AI in monoclonal cirrhotic nodules and the corresponding HCCs were analyzed with microsatellite polymorphic markers. RESULTS: One hundred one out of 180 nodules (56.1%) were monoclonal and the average fractional AI (FAI) was 21%, lower than the 40% in HCC. Their overall AI patterns differed significantly from that in HCC (P < 0.001) with FAI on 2q, 4q, 8p, and Xq higher than the mean value. Comparison of FAI in nodules (stratified by increasing total AI events) further revealed a progressive increase of FAI on 4q, 8p, and Xq. In contrast, FAI on 1p, 13q, 16q, and 17p were low in nodules but rose above the mean only in HCC. CONCLUSIONS: About half of the cirrhotic nodules are monoclonal and already have chromosome aberrations. AI on 4q, 8p, and Xq may be the earlier mutations, whereas AI on 1p, 13q, 16q, and 17p occurs late in hepatocarcinogenesis.

Adult↗

PubMed2001

Hepatitis B virus variants in patients receiving lamivudine treatment with breakthrough hepatitis evaluated by serial viral loads and full-length viral sequences.

Both viral loads and genome variations have been implicated in the pathogenesis of acute exacerbation of chronic hepatitis B. Hepatitis B exacerbation in patients receiving lamivudine treatment represented a unique setting to clarify their importance. Three organ recipients with posttransplantation hepatitis B exacerbation and 3 patients with chronic hepatitis B were studied. All received lamivudine treatment and their alanine aminotransferase (ALT) levels and hepatitis B virus (HBV) loads were regularly followed. Full-length genomic sequences before and during lamivudine treatment were determined in patients who had breakthrough of serum HBV DNA or elevation of serum ALT. Breakthrough of serum HBV DNA occurred after 6 to 15 months of lamivudine treatment in all. A rapid increase of viral load accompanying the emergence of tyrosine-methionine-aspartate-aspartate (YMDD) variant was followed by hepatitis B exacerbation in each patient. The mean number of nucleotide and amino acid substitutions per genome pair was equivalent in immunosuppressed or immunocompetent patients (6.3 vs. 6.3 for nucleotide, P >.05; 6.0 vs. 6.7 for amino acid, P >.05). Changes of nucleotide and amino acid beyond the YMDD motif were distributed along the whole HBV genome but none occurred within the known B-cell epitopes and human leukocyte antigen class I- or II-restricted T-cell epitopes. Our results suggest that a resurgence of viral load rather than changes of the known immunogenic viral epitopes is more closely associated with the development of hepatitis B exacerbation after the emergence of YMDD variants in patients receiving lamivudine treatment.

Adult↗

PubMed2001

Acute exacerbations of chronic hepatitis B are rarely associated with superinfection of hepatitis B virus.

There are 7 genotypes of hepatitis B virus (HBV). Whether superinfection of HBV carriers with different HBV genotypes occurs remains unknown. We therefore determined the HBV genotype and association between superinfection and acute exacerbation of disease in a cohort of 244 patients with chronic HBV infection who had elevated serum aminotransferase levels for at least 1 year. Within this group, 103 patients experienced acute exacerbation with an annual incidence of 13%, and 20 of the 103 patients had IgM antibody to hepatitis B core antigen (IgM anti-HBc). These 20 patients had a higher prevalence of genotype C infection (65%) than the remaining 83 anti-core IgM-negative patients (40%) who also had acute exacerbations (P <.05). Detailed analysis of HBV genotypes and sequences of the variable pre-S gene were determined in serial samples from 20 patients with IgM anti-HBc-positive acute exacerbations (group A), 20 patients with IgM anti-HBc-negative acute exacerbations (group B), and 20 patients without exacerbations (group C). Two (10%) of the group A patients had virologic evidence of HBV superinfection during acute exacerbation, one superinfected with heterotypic virus and the other with homotypic virus. The newly introduced virus disappeared after the exacerbation and the original virus resumed thereafter. The calculated prevalence of HBV superinfection in the hepatitis B carriers and those with acute exacerbations was 0.8% (2 of 244) and 1.9% (2 of 103), respectively. In conclusion, superinfection of HBV on hepatitis B carriers indeed occurs and may cause acute exacerbations, albeit at a low frequency even in hyperendemic areas of HBV infection.

Adolescent↗

PubMed2001

Specification of germ cell fates by FOG-3 has been conserved during nematode evolution.

Rapid changes in sexual traits are ubiquitous in evolution. To analyze this phenomenon, we are studying species of the genus Caenorhabditis. These animals use one of two different mating systems-male/hermaphroditic, like the model organism Caenorhabditis elegans, or male/female, like C. remanei. Since hermaphrodites are essentially females that produce sperm for self-fertilization, elucidating the control of cell fate in the germ line in each species could provide the key to understanding how these mating systems evolved. In C. elegans, FOG-3 is required to specify that germ cells become sperm. Thus, we cloned its homologs from both C. remanei and C. briggsae. Each species produces a single homolog of FOG-3, and RNA-mediated interference indicates that FOG-3 functions in each species to specify that germ cells develop as sperm rather than as oocytes. What factors account for the different mating systems? Northern analyses and RT-PCR data reveal that the expression of fog-3 is always correlated with spermatogenesis. Since the promoters for all three fog-3 genes contain binding sites for the transcription factor TRA-1A and are capable of driving expression of fog-3 in C. elegans hermaphrodites, we propose that alterations in the upstream sex-determination pathway, perhaps acting through TRA-1A, allow spermatogenesis in C. elegans and C. briggsae XX larvae but not in C. remanei.

Amino Acid Sequence↗

PubMed2001

Amebic liver abscess and human immunodeficiency virus infection: a report of three cases.

Invasive amebiasis rarely occurs in homosexual men and human immunodeficiency virus (HIV)-infected individuals and has not been regarded as a beacon for concomitant HIV infection. We encountered a bisexual man with a protracted course of amebic liver abscess and amebic colitis. In the presence of fever, generalized lymphadenopathy, and elevated serum aminotransferase levels, HIV infection was suspected and then confirmed by a de novo seroconversion of HIV antibody. Subsequently, we noted two consecutive patients with amebic liver abscess, also later found to be infected with HIV. The ameba obtained from these three cases was identified as Entamoeba histolytica by amplification of 16S ribosomal RNA by polymerase chain reaction and direct sequencing. This observation suggests that amebic liver abscess and colitis can be presentations for HIV infection in the Far East. Thus, the local patients with invasive amebiasis, especially those with a protracted course or with risk factors of HIV infection, should be tested for HIV.

AIDS-Related Opportunistic Infections↗

PubMed2001

The conserved serine 177 in the delta antigen of hepatitis delta virus is one putative phosphorylation site and is required for efficient viral RNA replication.

Hepatitis delta virus (HDV) small delta antigen (S-HDAg) plays a critical role in virus replication. We previously demonstrated that the S-HDAg phosphorylation occurs on both serine and threonine residues. However, their biological significance and the exact phosphorylation sites of S-HDAg are still unknown. In this study, phosphorylated S-HDAg was detected only in the intracellular compartment, not in viral particles. In addition, the number of phosphorylated isoforms of S-HDAg significantly increased with the extent of viral replication in transfection system. Site-directed mutagenesis showed that alanine replacement of serine 177, which is conserved among all the known HDV strains, resulted in reduced phosphorylation of S-HDAg, while the mutation of the other two conserved serine residues (2 and 123) had little effect. The S177A mutant dramatically decreased its capability in assisting HDV RNA replication, with a preferential and profound impairment of the antigenomic RNA replication. Furthermore, the viral RNA editing, a step relying upon antigenomic RNA replication, was also abolished by this mutation. These results suggested that phosphorylation of S-HDAg, with serine 177 as a presumable site, plays a critical role in viral RNA replication, especially in augmenting the replication of antigenomic RNA.

Amino Acid Sequence↗

PubMed2001

Molecular cloning and expression of woodchuck granulocyte-macrophage colony stimulating factor.

Granulocyte-macrophage colony stimulating factor (GM-CSF) has immunoregulatory and antiviral effects, and may thus be promising for the treatment of chronic hepatitis B. Using woodchuck hepatitis virus (WHV)-infected woodchuck as an animal model to test the efficacy and safety of GM-CSF on the therapy of chronic hepatitis B, woodchuck GM-CSF will be required due to the apparent species-specific activity of GM-CSF. The cDNA of woodchuck GM-CSF was cloned using reverse transcription-polymerase chain reaction (RT-PCR) with primers deriving from highly conserved regions of GM-CSF genes from other species. The deduced amino acids, including the signal peptide, is 138 in length and its identities to human, murine, canine and bovine GM-CSFs are 63, 49, 63, and 63% respectively. The genomic DNA of woodchuck GM-CSF was also cloned by PCR. Its organization is highly homologous to that of human and murine GM-CSF genes, consisting of four exons and three introns. Cloned woodchuck GM-CSF was expressed transiently in 293T cells. The recombinant protein expressed was found to stimulate the growth and differentiation of woodchuck bone marrow cells, indicating the protein expressed by the cloned gene is functional. These results pave the way for future studies on the potential role of GM-CSF for the treatment of chronic hepatitis B by using this animal model.

Amino Acid Sequence↗

PubMed2001

Prolonged interferon treatment after combination interferon and ribavirin therapy in patients with chronic hepatitis C: a clinical trial of interferon relapsers and non-responders.

BACKGROUND AND PURPOSE: For the retreatment of chronic hepatitis C patients relapsing after, or non-responsive to, previous interferon therapy, the efficacy of combination therapy with interferon alfa plus ribavirin is superior to interferon alone. The aim of this study was to determine whether prolonged interferon alfa treatment after 24-week combination therapy can further increase the efficacy of combination therapy. METHODS: Nineteen interferon relapsers and 17 interferon non-responders were randomly assigned to receive either interferon alfa 5 million units (MU) thrice weekly plus oral ribavirin 1,200 mg daily for 24 weeks (regimen A) or interferon alfa 5 MU thrice weekly plus oral ribavirin 1,200 mg daily for 24 weeks followed by interferon alfa 3 MU thrice weekly for another 24 weeks (regimen B). Efficacy was assessed by normalization of serum aminotransferase concentrations and disappearance of serum hepatitis C virus (HCV) RNA at the end of treatment and at 24 weeks after stopping treatment. RESULTS: Overall, 67% of relapsers receiving regimen A and 80% of those receiving regimen B had sustained virologic responses 24 weeks after stopping treatment. In contrast, 45% of non-responders receiving regimen A and 63% of those receiving regimen B had sustained responses. The sustained response was more common in relapsers with non-1b HCV genotypes. The sustained response rate to combination therapy was 50% or more in patients with genotype 1b infection. CONCLUSIONS: Prolonged interferon treatment after combination therapy has a comparable efficacy to combination therapy alone for the retreatment of chronic hepatitis C patients relapsing after, or non-responsive to, previous interferon therapy.

Adult↗

PubMed2001

Probable reinfection with hepatitis C virus in a chronic hepatitis C patient with a sustained response to combination therapy.

Superinfection with hepatitis C virus (HCV) in already chronically infected subjects has been documented. Whether a complete response to antiviral therapy is associated with protective immunity against reinfection with HCV remains unknown. We describe a patient who had a sustained biochemical and virologic response with loss of intrahepatic HCV RNA after a course of combination therapy using interferon plus ribavirin. Histopathologically, the chronic hepatitis was in remission on follow-up biopsy 6 months post-therapy. Unfortunately, 34 weeks post-therapy, a flare of hepatitis with reappearance of hepatitis C viremia was noted 2 months after he received injections from a non-licensed medical provider. Analysis of the core gene sequences showed a 95% homology between the HCV strains isolated before antiviral treatment and during the hepatitis flare. The data indicated that the hepatitis flare after a period of sustained response to combination therapy in this patient could have been caused by reinfection with homotypic HCV. Our observation indicates the lack of protective immunity against reinfection with HCV in patients with chronic hepatitis C, even after successful clearance of the virus. Therefore, reinforcing the education of these subjects to avoid HCV reinfection should be stressed.

Antiviral Agents↗

PubMed2000

Androgen-receptor gene CAG repeats, plasma testosterone levels, and risk of hepatitis B-related hepatocellular carcinoma.

BACKGROUND: Worldwide, hepatocellular carcinoma (HCC) is more prevalent in men than in women, suggesting that sex hormones and/or X-chromosome-linked genes may be involved in hepatocarcinogenesis. We investigated the association of a trinucleotide (CAG) repeat in the androgen receptor (AR) gene (located on the X chromosome) termed "AR-CAG repeats," levels of plasma testosterone, and the risk of HCC in Taiwanese men. Chronic hepatitis B virus (HBV) infection, which is associated with risk of HCC, is hyperendemic in Taiwan. METHODS: We compared the number of AR-CAG repeats in 285 HBV carriers with HCC and in 349 HBV carriers without HCC. We also conducted a nested case--control study on participants in a cohort study. Blood was collected prospectively from 110 case patients and 239 control subjects and was used to determine the number of AR-CAG repeats and plasma testosterone level. All statistical tests were two-sided. RESULTS: The overall odds ratio (OR) for HCC was 1.72 (95% confidence interval [CI] = 1.03--2.89) for HBV carriers with 20 or fewer AR-CAG repeats compared with those with more than 24 repeats. This association was observed only in patients with late-onset HCC (OR = 2.37; 95% CI = 1.28--4.38). In the nested case-control study, HBV carriers in the highest tertile of testosterone levels had a statistically significantly increased risk of HCC (OR = 2.06; 95% CI = 1.14--3.70) compared with those in the lowest tertile. Elevated testosterone was more strongly associated with early-onset (OR = 4.67; 95% CI = 1.41--15.38) than late-onset disease. HBV carriers with 20 or fewer AR-CAG repeats and higher testosterone levels had a fourfold increase in HCC risk compared with those with more than 24 repeats and testosterone levels in the lowest tertile. CONCLUSIONS: Higher levels of androgen signaling, reflected by higher testosterone levels and 20 or fewer AR-CAG repeats, may be associated with an increased risk of HBV-related HCC in men.

Adenine↗

PubMed2000

Familial risk of hepatocellular carcinoma among chronic hepatitis B carriers and their relatives.

BACKGROUND: Familial predisposition as a risk factor for hepatocellular carcinoma (HCC) in hepatitis B virus (HBV) carriers has not been thoroughly explored. METHODS: The HCC risk associated with having parents and/or siblings with HCC was evaluated by use of a cohort study of 4808 male HBV carriers. A case-control family study was also conducted on data from first-degree relatives of 553 HBV carriers who had newly diagnosed HCC (case subjects) and 4684 HBV carriers without HCC (control subjects). RESULTS: In the cohort study, HBV carriers with a family history of HCC had a multivariate-adjusted rate ratio for HCC of 2.41 (95% confidence interval [CI] = 1.47-3.95) compared with HBV carriers without a family history of HCC. For carriers with two or more affected relatives, the ratio increased to 5.55 (95% CI = 2.02-15.26). Cumulative HCC risk by age 70 years was 235.6 per 1000 (95% CI = 95. 3-375.9 per 1000) for HBV carriers with family history compared with 88.9 per 1000 (95% CI = 67.9-109.9 per 1000) for those without. In the case-control family study, first-degree relatives of case subjects were more likely to have HCC (age-sex-adjusted odds ratio [OR] = 2.57; 95% CI = 2.03-3.25) than first-degree relatives of control subjects. The excess risk of HCC among relatives was particularly evident in siblings (sisters-age-adjusted OR = 4.55 [95% CI = 2.22-9.31]; brothers-age-adjusted OR = 3.73 [95% CI = 2. 64-5.27]), but it was also observed in parents. The cumulative risk of HCC to age 80 years was 83.0 per 1000 among relatives of case subjects and 42.0 per 1000 among relatives of control subjects. Among relatives of case subjects, the cumulative risk of HCC was greater if the case subjects were diagnosed before age 50 years (two-sided P =.047). Liver cirrhosis was 2.29 (95% CI = 1.68-3.11) times more frequent in relatives of case subjects than in relatives of control subjects. CONCLUSIONS: First-degree relatives of patients with HBV-related HCC appear to be at increased risk of HCC and should be considered in the formulation of HCC-screening programs.

Adult↗

PubMed2000

A novel member of the tob family of proteins controls sexual fate in Caenorhabditis elegans germ cells.

Although many cell fates differ between males and females, probably the most ancient type of sexual dimorphism is the decision of germ cells to develop as sperm or as oocytes. Genetic analyses of Caenorhabditis elegans suggest that fog-3 might directly control this decision. We used transformation rescue to clone the fog-3 gene and show that it produces a single major transcript of approximately 1150 nucleotides. This transcript is predicted to encode a protein of 263 amino acids. One mutation causes a frame shift at the sixth codon and is thus likely to define the null phenotype of fog-3. Although the carboxyl-terminus of FOG-3 is novel, the amino-terminal domain is similar to that of the Tob, BTG1, and BTG2 proteins from vertebrates, which might suppress proliferation or promote differentiation. This domain is essential for FOG-3 activity, since six of eight missense mutations map to this region. Furthermore, this domain of BTG1 and BTG2 interacts with a transcriptional regulatory complex that has been conserved in all eukaryotes. Thus, one possibility is that FOG-3 controls transcription of genes required for germ cells to initiate spermatogenesis rather than oogenesis. This model implies that FOG-3 is required throughout an animal's life for germ cells to initiate spermatogenesis. We used RNA-mediated interference to demonstrate that fog-3 is indeed required continuously, which is consistent with this model.

Amino Acid Sequence↗