Genetics of sex determination in eukaryotes

Fasting lipid and lipoproteins concentrations in pregnant women with a history of migraine

BACKGROUND

Migraine is associated with a number of cardiometabolic risk factors including abnormalities in lipid metabolism. However, little is known about these associations among pregnant migraineurs. We conducted the present study to evaluate the extent to which altered lipid profiles are associated with history of migraine among pregnant women.

METHODS

A cohort of 1062 Peruvian women were interviewed at 24-28 weeks of gestation. Migraine status was classified based on the International Classification of Headache Disorders-II diagnostic criteria. Serum lipid concentrations were measured enzymatically using standardized assays. Multivariable logistic regression was used to estimate adjusted odds ratios (AORs) and 95% confidence intervals (CIs) as measures of associations of migraine status with varying concentrations of lipids and lipoproteins during pregnancy.

RESULTS

Approximately 18.5% of the study participants were identified as migraineurs (196 of 1062). Maternal serum total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglycerides, and total cholesterol : HDL ratio were all statistically significantly elevated among pregnant migraineurs compared with pregnant non-migraineurs. In multivariate adjusted models, pregnant women with migraine had higher odds of elevated total cholesterol, LDL, and total cholesterol : HDL ratio as compared with pregnant women without migraine. For instance, the AOR and 95% CI for successive quartiles of the total cholesterol associated with history of migraine were Q2 (219-247 mg/dL): 1.05 (0.64-1.70), Q3 (248-281 mg/dL): 1.16 (0.72-1.86), and Q4 (≥282 mg/dL): 1.87 (1.20-2.91) with the lowest quartile (<219 mg/dL) as the referent group (P value for trend = .003). Obese women with elevated total cholesterol (≥282 mg/dL) were more likely to be migraineurs (OR = 3.71; 95% CI 1.58-8.71) as compared with non-obese women with lower total cholesterol (<219 mg/dL). Similar elevated odds of migraine were observed for obese women with elevated LDL cholesterol, elevated triglycerides and high total cholesterol : HDL ratio.

CONCLUSION

Pregnant migraineurs had elevated odds of dyslipidemia, particularly hypercholesterolemia, elevated LDL, and total cholesterol : HDL ratio as compared with pregnant non-migraineurs. The observed associations were more pronounced among obese migraineurs. Our findings add to the accumulating evidence of adverse cardiometabolic risk profiles among migraineurs and extend these associations to pregnant women.

The evolutionary dynamics of sex determination

REVIEW There is substantial cytogenetic data indicating that the process of sex determination can evolve relatively rapidly. However, recent molecular studies on the evolution of the regulatory genes that control sex determination in the insect Drosophila melanogaster, the nematode Caenorhabditis elegans, and mammals suggest that, although certain sex determination regulatory genes have evolved relatively rapidly, other sex determination regulatory genes are quite conserved. Thus, studies of the evolution of sex determination, a process that appears to have elements that undergo substantial evolutionary change and others that may be conserved, could provide substantial insights into the kinds of forces that both drive and constrain the evolution of developmental hierarchies.

Understanding human sexuality--specifically homosexuality and the paraphilias--in terms of chaos theory and fetal development

This paper considers human sexual orientation, specifically homosexuality and some paraphilias, to occur as a result of intrauterine development, itself a mathematically chaotic process. Parameter space, an example of state space in the phase diagram, has been used to illustrate different phenotypes. The crossing of a bifurcation boundary by the developing fetus is proposed as a mechanism by which it may be changed from one sexual orientation to another, e.g. from heterosexuality to homosexuality. The factors which push the fetus over a bifurcation boundary, which include a Y-chromosome, specific hormone administration, the lying contiguous to an opposite-sex fetus in multiple pregnancies, maternal stress and immune factors are described. The syndromes congenital renal hyperplasia and the androgen insensitivity syndrome and their relevance to this model are also discussed. Finally, chaos theory is used to encompass the complex interactions between fetal development and cultural factors in human sexuality.

Drosophila spermatogenesis as a model system

Spermatogenesis is very similar throughout the animal kingdom and is probably based on very old evolutionarily principles. Drosophila can serve as a suitable model system to understand the underlying processes. The molecular and ultrastructural data obtained for Drosophila germ cell development can be applied to understanding spermatogenesis in other organisms, including humans. Various methods used in studies of Drosophila spermatogenesis are presented together with observations which exemplify this conclusion.

The evolution of heteromorphic sex chromosomes

The facts and ideas which have been discussed lead to the following synthesis and model. 1. Heteromorphic sex chromosomes evolved from a pair of homomorphic chromosomes which had an allelic difference at the sex-determining locus. 2. The first step in the evolution of sex-chromosome heteromorphism involved either a conformational or a structural difference between the homologues. A structural difference could have arisen through a rearrangement such as an inversion or a translocation. A conformational difference could have occurred if the sex-determining locus was located in a chromosomal domain which behaved as a single control unit and involved a substantial segment of the chromosome. It is assumed that any conformational difference present in somatic cells would have been maintained in meiotic prophase. 3. Lack of conformational or structural homology between the sex chromosomes led to meiotic pairing failure. Since pairing failure reduced fertility, mechanisms preventing it had a selective advantage. Meiotic inactivation (heterochromatinization) of the differential region of the X chromosome in species with heterogametic males and euchromatinization of the W in species with heterogametic females are such mechanisms, and through them the pairing problems are avoided. 4. Structural and conformational differences between the sex chromosomes in the heterogametic sex reduced recombination. In heterogametic males recombination was reduced still further by the heterochromatinization of the X chromosome, which evolved in response to selection against meiotic pairing failure. 5. Suppression of recombination resulted in an increase in the mutation rate and an increased rate of fixation of deleterious mutations in the recombination-free chromosome regions. Functional degeneration of the genetically isolated regions of the Y and W was the result. In XY males this often led to further meiotic inactivation of the differential region of the X chromosome, and in this way an evolutionary positive-feedback loop may have been established. 6. Structural degeneration (loss of material) followed functional degeneration of Y or W chromosomes either because the functionally degenerate genes had deleterious effects which made their loss a selective advantage, or because shorter chromosomes were selectively neutral and became fixed by chance. 7. The evolutionary routes to sex-chromosome heteromorphism in groups with female heterogamety are more limited than in those with male heterogamety. Oocytes are usually large and long-lived, and are likely to need the products of X- or Z-linked genes. Meiotic inactivation of these chromosomes is therefore unlikely. In the oocytes of ZW females, meiotic pairing failure is avoided through euchromatinization of the W rather than heterochromatinization of the Z chromosome.(ABSTRACT TRUNCATED AT 400 WORDS)

Sex in flies: the splice of life

The discovery that the primary transcripts of many genes are processed to produce more than one kind of messenger RNA focuses attention on the control of RNA processing as a developmental regulatory mechanism. In the fruit-fly Drosophila melanogaster, differential splicing of a hierarchy of regulatory genes determines sex, and thus the molecular biology of sex determination in the fruit-fly may lead to insights into the mechanisms by which alternative splicing is regulated.

Drosophila doublesex gene controls somatic sexual differentiation by producing alternatively spliced mRNAs encoding related sex-specific polypeptides

The doublesex (dsx) gene regulates somatic sexual differentiation in both sexes in D. melanogaster. Two functional products are encoded by dsx: one product is expressed in females and represses male differentiation, and the other is expressed in males and represses female differentiation. We have determined that the dsx gene is transcribed to produce a common primary transcript that is alternatively spliced and polyadenylated to yield male- and female-specific mRNAs. These sex-specific mRNAs share a common 5' end and three common exons, but possess alternative sex-specific 3' exons, thus encoding polypeptides with a common amino-terminal sequence but sex-specific carboxyl termini. Genetic and molecular data suggest that sequences including and adjacent to the female-specific splice acceptor site play an important role in the regulation of dsx expression by the transformer and transformer-2 loci.