High frequency in vivo loss of heterozygosity is primarily a consequence of mitotic recombination

We have used the adenine phosphoribosyltransferase gene (APRT; 16q24) to investigate the mechanisms of loss of heterozygosity (LOH) in normal human somatic cells in vivo. APRT-deficient (APRT-/-, APRT-/0) T lymphocytes from the peripheral blood of four obligate APRT heterozygotes (APRT+/-) with characterized germ-line mutations were selected in medium containing 100 microM 2,6-diaminopurine. A total of 80 2,6-diaminopurine-resistant T-cell clones from 2 of the heterozygotes were analyzed for this study. The presence or absence of LOH of proximal linked microsatellite repeat markers was used to divide the clones into two groups: (a) those in which LOH was likely due to localized changes in APRT (e.g., point mutations); and (b) those with LOH at additional loci. A total of 61 clones (76%) exhibited LOH of linked microsatellite repeat markers at different locations on 16q, which extended from the smallest measured region (<5.5 cM) to the entire 16q arm. The remaining 19 clones (24%) had point mutations in APRT or other relatively minor alterations. Ten clones with LOH encompassing different regions of 16q were examined by conventional cytogenetics and by fluorescence in situ hybridization using an APRT cosmid probe. All clones exhibited a normal diploid karyotype, and nine exhibited two copies of APRT. The one clone that was hemizygous for APRT had the smallest observed region of LOH in clones from that individual. These results indicate that mitotic recombination and, to a much lesser extent, deletion may be the primary mechanisms for the relatively high frequency of in vivo LOH observed in normal human T cells. Because LOH leads to the expression of recessive tumor suppressor genes in many cancers, these data have significant implications for the role of LOH in the early stages of tumor development, especially in breast cancer.

Localization of group IIc low molecular weight phospholipase A2 mRNA to meiotic cells in the mouse

We use in situ hybridization to demonstrate that the testicular expression of a novel, mouse, low molecular weight phospholipase A2 (PLA2 Group IIc) mRNA is specific to cells undergoing meiosis. A complete cDNA (1421 bp) encoding the mouse Pla2g2c gene was generated with reverse transcription-PCR (RT-PCR) and 5' and 3' RACE (rapid amplification of cDNA ends) RT-PCR, and its nucleotide sequence was determined. Northern blots of RNA from different tissues revealed a single 1.6 kb transcript only in testis. In situ hybridization indicated that this mouse gene is transcribed mainly in pachytene spermatocytes, secondary spermatocytes, and round spermatids. Expression of the gene is seen in all stages of the seminiferous epithelium, especially in stages VI-VII.

Loss of heterozygosity analysis in a human fibrosarcoma cell line

Loss of heterozygosity (LOH) is an important event in tumor formation. We have used polymorphic microsatellite repeat markers to identify and characterize LOH in spontaneous mutants of a human cell line, MR12-1, that is heterozygous for the adenine phosphoribosyltransferase gene (APRT+/-) located on chromosome 16q24.3. Initially, clones without extensive LOH (which are likely derived as a consequence of intragenic point mutations) and clones with multilocus LOH (which are likely due to major chromosome alterations) were identified. Clones with major regions of LOH were further characterized by assaying additional informative microsatellite markers. Analysis of 20 spontaneously-arising, independent APRT-/- clones from MR12-1 demonstrated that nine of the mutants retained both copies of APRT and 11 had undergone multilocus genetic alterations. The nature of LOH in four of the latter clones has been examined in detail by karyotype and fluorescence in situ hybridization analysis (Shao et al., 1996). These data demonstrate that LOH of chromosome 16 may be due to mitotic recombination, interstitial or partial deletion, or to more complex mechanisms. LOH in these clones may be a consequence of events similar to those observed in many tumors.

Sexually transmitted disease control in China (1949-1994)

This paper summarizes the historical experiences in venereal disease control in China during the 1950s. Venereal diseases had been all but eliminated in the whole country till 1964. However, along with the implementation of open-door policy and economic reform in the 1980s, the social environment was changed to a great extent in this country. Sexually transmitted diseases (STDs) were re-introduced in the Chinese mainland and new foci of infection established themselves in some cities. During the recent 8 years the national STD case-reporting and sentinel surveillance systems have been set up. The results of surveillance show that the annual incidence of STD has been on the increase. The existing factors associated with the increasing incidence of STD mainly are; population movement, increasing affluence in a part of population, the availability of multiple sexual partners (including the prostitution) and asymptomatic STD increased. Finally, the strategies for STD control are discussed in detail.

APRT: a versatile in vivo resident reporter of local mutation and loss of heterozygosity

We describe an in vivo mutagenesis model that utilizes reverse mutation and forward mutation at the endogenous Aprt locus. Reverse mutation provides an in situ method for detecting environments or agents that cause point mutations. Forward mutation detects large chromosomal events, including mitotic recombination, chromosome loss, and large multilocus deletion, all of which can lead to loss of heterozygosity. Detection of reverse mutation in vivo is based on the differential capacity of Aprt and Aprt cells to sequester radiolabeled adenine by catalyzing its conversion to adenosine monophosphate with subsequent incorporation into nucleic acids. Cells lacking APRT activity cannot accumulate exogenously administered, tagged adenine, whereas Aprt+ cells can and will thereby become marked. Thus, genetically modified mice with mutant but revertible Aprt alleles should be a useful vehicle for in situ detection of mutagenic activity in the whole animal. the feasibility of this model has been illustrated, first, by showing that APRT-deficient mice are viable and, second, by demonstrating that the minority of Aprt+ cells within a chimeric tumor growing in an Aprt+ mouse can be selectively labeled following IP injection of [14C]-adenine and can be identified by autoradiography. Forward mutation, detected by growth in selective medium of primary cells derived from Aprt+/- heterozygous mice, provides on independent estimate of in vivo mutation frequency. The frequency with which Aprt colonies arise provides a measure of the frequency of Aprt(-)-negative cells in the tissue at that point in time. Culture of skin fibroblasts in 2,6-diaminopurine (DAP) produced Aprt+ colonies with a frequency of about 10(-4). This frequency is similar to that found for human T lymphocytes from individuals heterozygous at the Aprt locus. In both cases, the majority of mutagenic events involved allele loss. Polymerase chain reaction with linked polymorphic microsatellites on mouse chromosome 8 demonstrated that allele loss was mediated mostly by mitotic recombination, as was the case for human T lymphocytes. The high frequency of mitotic recombination and allele loss at a neutral locus has significant implications for the process of tumorigenesis and argues that spontaneous or induced mitotic recombination may play a causal role in the progression to cancer.

Complex chromosomal mechanisms lead to APRT loss of heterozygosity in heteroploid cells

Loss of the wild-type allele of a tumor suppressor gene, or loss of heterozygosity (LOH), is one of the most important mechanisms of carcinogenesis. Adenine phosphoribosyltransferase (APRT) has been used as a surrogate marker for tumor suppressor genes. We have previously shown that APRT deficiency in an APRT heterozygous human cell line, MR12-1, was predominantly caused by the loss of the remaining wild-type allele. Here we report the characterization of the chromosomal pathways leading to LOH in four clones derived from this heteroploid cell line. We performed karyotype analysis, chromosome 16-specific painting, and fluorescence in situ hybridization with an APRT-containing cosmid on these clones and their heteroploid parental cells. Our findings suggest that LOH occurs in tetraploid as well as diploid cells, and that diploid cells with LOH may undergo endoreduplication to attain tetraploidy. Our results also suggest that, in addition to LOH being caused by a single event (such as mitotic recombination or deletion), LOH may be caused by a combination of sequential events, such as mitotic recombination or translocation followed by chromosome loss. The instability of the genomes of the parental cells may have provided a greater diversity of options for genetic evolution. Similar karyotypic evolution may occur at late stages of carcinogenesis in vivo.

[The application of the pattern visual-evoked potential in the diagnosis and treatment of amblyopia]

PURPOSE

To research into the value of the application in the diagnosis and treatment of amblyopia, and to discuss the mechanism of amblyopia.

METHODS

The subjects were divided into three groups: 108 amblyopia eyes; 180 normal eyes and 26 amblyopia eyes during the treatment with Madopar. PVEP was observed with black-white checks pattern-reversal stimulation at several spatial frequencies (30', 60', 90').

RESULTS

P1 latency of the amblyopia eyes prolongs at the high frequency (30' angle of view), in which the occurrence rate of abnormal PVEP is 68.5%. Through detecting PVEP during the treatment of amblyopia with Madopar, we found P1 latency shortened and amplitude increased (P < 0.05).

CONCLUSION

It is better to use P1 latency to observe the visual function of patients with amslyopia with stimulation at 30' angle of view. PVEP is an important objective index in diagnosis and evaluating the curative effect of amblyopia.

Genetic study of indirect inguinal hernia

We performed a genetic analysis of 280 families with congenital indirect inguinal hernia ascertained in Shandong province. The multifactorial threshold model and segregation analysis were applied to these families to investigate the mode of inheritance of congenital indirect inguinal hernia. Our results indicate that congenital indirect inguinal hernia is not compatible with a multifactorial threshold model, and the frequent vertical transmission and high segregation ratio suggest autosomal dominant inheritance with incomplete penetrance and sex influence. Through further pedigree analysis of the multiple case families with at least two closely related affected members, we noted preferential paternal transmission of the disease gene, which might suggest the role of genomic imprinting in the aetiology of this condition.

Prevalence and epidemiologic correlates of sexually transmitted Chlamydia trachomatis infection in a selected population

The incidence of Chlamydia trachomatis genitourinary infection was found by enzyme immunoassay antigen detection to be 10.0% in patients attending a sexually transmitted disease (STD) clinic, 3.0% in clients visiting an obstetrics-gynecology clinic, 20.8% in female prostitutes, and 1.3% in sexually active men. Predisposing factors for chlamydial infection were young age, multiple sexual partners, history of STDs, and coinfection with other STDs. Abnormal vaginal discharge and cervices in women, but not urethral manifestations in men, were significantly associated with chlamydial infection. Urethral gram stain had a certain value in identifying men infected with C. trachomatis.

STD epidemiologic analysis at national surveillance spots in the period 1987-1990

This article summarizes surveillance data of STDs at 16 urban monitoring centers in 1987-1990. During the four year period, 125,493 STD cases were reported. The average annual incidence was 77.80/100,000. Because the rate of increase in females (65.85% per year) was greater than that in males (36.81% per year), the male-to-female ratio fell from 2.39:1 (1987) to 1.34:1 (1990). The number of STD cases reported from all centers tended to increase, and the overall rate of increase was 46.61% per year. The major disease was gonorrhea, with a constituent ratio of 59.22% (1990). However, condyloma acuminatum and nongonococcal urethritis had greater rates of increase (105.03% and 85.14% per year, respectively). The 20-39 year age group accounted for 82.10% of total cases, for STD patients were mostly in the sexually active population. The STD incidence among self-employed businessmen (1206.06/100,000, in 1990) was highest among professional populations. According to analysis of different regions, STD incidence was highest in the southern cities (203.00/100,000, 1990). The greatest rate of increase of STDs was in Yangtze River Valley cities, where the average annual rate of increase was 71.41%.

[Ca2+ channel blocking effect of panaxadiol saponins and panaxatriol saponins of cultured cardiac cells]

It was found that PDS and PTS decreased the action potential parameters of the cultured myocardiocytes in a dosage-dependent way. The effects of PDS 1000 micrograms/ml, PTS 200 micrograms/ml were in correspondence with the known Ca2+ channel blocker Mn2+ 0.05 micrograms/ml. Washing out, administration of epinephrine 10 micrograms/ml or Ca2+ 80 micrograms/ml were able to reverse the action potential from inhibition. The above results indicate that both PDS and PTS have Ca2+ channel blockade action.

An extra maternally derived X chromosome is deleterious to early mouse development

An extra copy of the X chromosome, unlike autosomes, exerts only minor effects on development in mammals including man and mice, because all X chromosomes except one are genetically inactivated. Contrary to this contention, we found that an additional maternally derived X (XM) chromosome, but probably not a paternally derived one (XP), consistently contributes to early death of 41,XXY and 41,XXX embryos in mice. Because of imprinted resistance to inactivation, two doses of XM remain active in the trophectoderm, and seem to be responsible for the failure in the development of the ectoplacental cone and extraembryonic ectoderm, and hence, from early embryonic death. Discordant observations in man indicating viability of XMXMXP and XMXMY individuals suggest that imprinting on the human X chromosome is either weak, unstable or erased before the initiation of X-inactivation in progenitors of extraembryonic membranes.