SummaryThree key steps in meiosis allow diploid organisms to produce haploid gametes: (1) homologous chromosomes (homologs) pair and undergo crossovers; (2) homologs segregate to opposite poles; and (3) sister chromatids segregate to opposite poles. The XX/XO sex determination system found in many nematodes [1] facilitates the study of meiosis because variation is easily recognized [2, 3, 4]. Here we show that meiotic segregation of X chromosomes in the trioecious nematode Auanema rhodensis [5] varies according to sex (hermaphrodite, female, or male) and type of gametogenesis (oogenesis or spermatogenesis). In this species, XO males exclusively produce X-bearing sperm [6, 7]. The unpaired X precociously separates into sister chromatids, which co-segregate with the autosome set to generate a functional haplo-X sperm. The other set of autosomes is discarded into a residual body. Here we explore the X chromosome behavior in female and hermaphrodite meioses. Whereas X chromosomes segregate following the canonical pattern during XX female oogenesis to yield haplo-X oocytes, during XX hermaphrodite oogenesis they segregate to the first polar body to yield nullo-X oocytes. Thus, crosses between XX hermaphrodites and males yield exclusively male progeny. During hermaphrodite spermatogenesis, the sister chromatids of the X chromosomes separate during meiosis I, and homologous X chromatids segregate to the functional sperm to create diplo-X sperm. Given these intra-species, intra-individual, and intra-gametogenesis variations in the meiotic program, A. rhodensis is an ideal model for studying the plasticity of meiosis and how it can be modulated.

Obese patients with atrial fibrillation (AF) are frequently managed with AF ablation. We sought to examine whether there exists a body mass index (BMI) threshold beyond which odds of experiencing a complication from AF ablation increase. All patients enrolled in the Vanderbilt AF Registry who underwent catheter-based AF ablation from May 1999 to February 2012 were included. Major complications were recorded. Morbid obesity was defined as BMI >40 kg/m2, and BMI as a continuous variable was examined in multivariable analysis. Thirty-five complications (6.8%) occurred in 512 ablations. Morbidly obese patients experienced a higher rate of complications (6/42, 14.3%) than non-morbidly obese (29/470, 6.2%) (P=0.046). Using a discrete BMI cut-off, the odds of complications increased 3.1-fold in those with morbid obesity (odds ratio [OR] 3.1, 95% Confidence Interval [CI] 1.1–8.4, P=0.03) and 2.1-fold by female gender (OR 2.1, 95% CI 1.04–4.38, P=0.04). With BMI as a continuous variable, the odds of complications increased by 5% per 1 unit increase in BMI (OR 1.05, 95% CI 1.0–1.11, P=0.05) and there was a 2.2-fold increase by female gender (OR 2.2, 95% CI 1.1–4.6, P=0.03). In conclusion, morbid obesity represents a BMI threshold above which the odds of complications with AF ablation significantly increase. The increase in complications appears to be driven primarily by events in women suggesting that morbidly obese women are a special population to consider when considering AF ablation.

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