Time to Pregnancy: A Computational Method for Using the Duration of Non-Conception for Predicting Conception

An important problem in reproductive medicine is deciding when people who have failed to become pregnant without medical assistance should begin investigation and treatment. This study describes a computational approach to determining what can be deduced about a couple''s future chances of pregnancy from the number of menstrual cycles over which they have been trying to conceive. The starting point is that a couple''s fertility is inherently uncertain. This uncertainty is modelled as a probability distribution for the chance of conceiving in each menstrual cycle. We have developed a general numerical computational method, which uses Bayes'' theorem to generate a posterior distribution for a couple''s chance of conceiving in each cycle, conditional on the number of previous cycles of attempted conception. When various metrics of a couple''s expected chances of pregnancy were computed as a function of the number of cycles over which they had been trying to conceive, we found good fits to observed data on time to pregnancy for different populations. The commonly-used standard of 12 cycles of non-conception as an indicator of subfertility was found to be reasonably robust, though a larger or smaller number of cycles may be more appropriate depending on the population from which a couple is drawn and the precise subfertility metric which is most relevant, for example the probability of conception in the next cycle or the next 12 cycles. We have also applied our computational method to model the impact of female reproductive ageing. Results indicate that, for women over the age of 35, it may be appropriate to start investigation and treatment more quickly than for younger women. Ignoring reproductive decline during the period of attempted conception added up to two cycles to the computed number of cycles before reaching a metric of subfertility.     

Analysis of mutation in human cells by using an Epstein-Barr virus shuttle system.

We developed highly sensitive shuttle vector systems for detection of mutations formed in human cells using autonomously replicating derivatives of Epstein-Barr virus (EBV). EBV vectors carrying the bacterial lacI gene as the target for mutation were established in human cells and later returned to Escherichia coli for rapid detection and analysis of lacI mutations. The majority of the clonal cell lines created by establishment of the lacI-EBV vector show spontaneous LacI- frequencies of less than 10(-5) and are suitable for studies of induced mutation. The ability to isolate clonal lines represents a major advantage of the EBV vectors over transiently replicating shuttle vectors (such as those derived from simian virus 40) for the study of mutation. The DNA sequence changes were determined for 61 lacI mutations induced by exposure of one of the cell lines to N-nitroso-N-methylurea. A total of 33 of 34 lacI nonsense mutations and 26 of 27 missense mutations involve G X C to A X T transitions. These data provide support for the mutational theory of cancer.     

Guidelines for the Control of Human Immunodeficiency Virus Infection in Adolescents

Although adolescents account for only 0.4% of reported cases of the acquired immunodeficiency syndrome (AIDS) in the United States, they are sexually active and, therefore, at risk of acquiring human immunodeficiency virus (HIV) infection. To address issues of HIV control in adolescents, we developed guidelines that emphasize education and medical care and deemphasize antibody testing. For adolescents known to be infected with HIV, we recommend no restrictions on access to educational or treatment programs except when their health providers recommend such restrictions to protect them from exposure to opportunistic infections. For adolescents of unknown antibody status with a possible previous exposure to HIV, we recommend that as long as the incidence of HIV infection and clinical AIDS remains low, there should be no restrictions on residential placements and no routine antibody testing.     

Two linear plasmids in mitochondria of Fusarium solani f. sp. cucurbitae

Two linear plasmid-like DNAs designated pFSC1 (9.2 kbp) and pFSC2 (8.3 kbp) were found in an isolate of the plant pathogenic fungus Fusarium solani f. sp. cucurbitae race 1. The plasmids were maternally inherited and copurified with mitochondrial DNA obtained from a mitochondria-enriched cell fraction suggesting that they are located in mitochondria. The plasmids did not share extensive sequence similarity. No homology was detected between either plasmid and the nuclear or mitochondrial genome when cloned plasmids were used as probes in Southern hybridization analyses. The fungus was cured of plasmids by ethidium bromide treatment. Compared to the plasmid-containing isolate, plasmid-cured derivatives had reduced pathogenicity on a susceptible plant host, Cucurbita maxima "Pink Banana."     

The a and b loci of Ustilago maydis hybridize with DNA sequences from other smut fungi.

The smut fungi are obligately parasitic during the sexual phase of their life cycle, and the mating-type genes of these fungi play key roles in both sexual development and pathogenicity. Among species of smut fungi it is common to find a bipolar mating system in which one locus with two alternate alleles is believed to control cell fusion and establishment of the infectious cell type. Alternatively, several species have a tetrapolar mating system in which two different genetic loci, one of which has multiple alleles, control fusion and subsequent development of the infection hyphae. Cloned sequences from the a and b mating-type loci of the tetrapolar smut fungus Ustilago maydis were used as hybridization probes to DNAs from 23 different fungal strains, including smut fungi with both tetrapolar and bipolar mating systems. In general, all of the smut fungi hybridized with the mating-type genes from U. maydis, suggesting conservation of the sequences involved in mating interactions. A selection of DNAs from other ascomycete and basidiomycete fungi failed to hybridize with the U. maydis mating-type sequences. Exceptions to this finding include hybridization of DNA from the a1 idiomorph of U. maydis to DNA from one strain of U. violacea and hybridization of both a idiomorphs to DNA from Saccharomyces cerevisiae.     

A model for intracellular calcium signaling and the coordinate regulation of hormone biosynthesis, receptors and secretion.

A two-state model for the stimulus-induced nongraded response of a single cell is formulated. Individual metestrus gonadotropes stimulated with LHRH operate as a simple switch: either on or off. At a given concentration of stimulus some gonadotropes switch on, while others do not switch on, secretion. The probability of a gonadotrope being in the secretory state is enhanced with each increment of LHRH concentration. Individual gonadotropes in a secretory state are envisioned to decrease their number of LHRH receptors and to switch off LH biosynthesis. On the other hand, individual gonadotropes that are not in a secretory state are thought to increase their number of LHRH receptors and to switch on LH biosynthesis. The group of individuals in the population that have thresholds falling in the range of a given stimulus initiate secretion. And, the group of individuals in the population that have thresholds that fall above the range of a given stimulus do not initiate secretion. More remarkable is evidence that the cells that are protected from hormone secretion nevertheless respond with a set of intracellular signals and this provides a new perspective of how they switch on hormone biosynthesis and up-regulate the LHRH receptors. These changes are envisioned to reduce the threshold of an individual cell and accordingly to enhance the probability that the cell responds in the secretory state with the next stimulus. This scheme would appear to lead to automatic cycles of secretion and biosynthesis since an individual cell can occupy only one of two states at any time and occupancy of either state promotes change to the other. This may provide a solution to the problem of how an endocrine gland might reconcile differences in the time-course of hormone secretion which occurs rapidly and hormone biosynthesis that requires a longer period of time. Parenthetically, the model may also be adapted to the case where the vast majority of individuals in the population are generally subthreshold in relation to the physiological stimulus: such an adaption leads to interesting ways of viewing the mammalian reproductive cycle and the regulation of the preovulatory LH surge. A two-state model of the internal Ca2+ store is outlined here to stimulate thought on how the intracellular signals of each binary state may switch a variety of cellular responses either on or off. The model provides a new perspective on the coordinate regulation of hormone biosynthesis, receptors, and secretion that may be useful in the final reconciliation of population studies with insights about individual cells.     

Human mast cell proteases hydrolyze neurotensin, kinetensin and Leu5-enkephalin.

Purified mast cell carboxypeptidase cleaved the C-terminal leucines from Leu5-enkephalin (Leu-ENK), neurotensin (NT), and kinetensin (KT), with Km values of 36, 16, and 15 microM, and kcat values of 44, 51, and 53 s-1, respectively. To better predict potential in vivo hydrolysis products generated by mast cell proteases, these peptides were incubated with released skin mast cell supernatants. Leu5-enkephalin was hydrolyzed only by carboxypeptidase. Kinetensin was cleaved by tryptase, chymase, and carboxypeptidase to yield KT(1-3), KT(1-7), KT(1-8), KT(4-7), and KT(4-8), the last two peptides by the concerted action of two of the proteases. NT(1-11) and NT(1-12) were generated from neurotensin by chymase and carboxypeptidase, respectively.