Hybrid breakdown is a type of reproductive failure that appears after the F 2 generation of crosses between different species or subspecies. It is caused by incompatibility between interacting genes. Genetic analysis of hybrid breakdown, particularly in higher animals, has been hampered by its complex nature (i.e., it involves more than two genes, and the phenotype is recessive). We studied hybrid breakdown using a new consomic strain, C57BL/6J-X MSM , in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M. m. molossinus). Males of this consomic strain are sterile, whereas F 1 hybrids between C57BL/6J and MSM/Ms are completely fertile. The C57BL/6J-X MSM males showed reduced testis weight with variable defects in spermatogenesis and abnormal sperm head morphology. We conducted quantitative trait locus (QTL) analysis for these traits to map the X-linked genetic factors responsible for the sterility. This analysis successfully detected at least three distinct loci for the sperm head morphology and one for the testis weight. This study revealed that incompatibility of interactions of X-linked gene(s) with autosomal and/or Y-linked gene(s) causes the hybrid breakdown between the genetically distant C57BL/6J and MSM/Ms strains. H YBRIDS between individuals of two genetically di-Hybrid breakdown is another type of reproductive isolation, defined as inviability or sterility observed only verged populations show different extents of rein the F 2 or later generations of interspecific or intersubproductive failure; this failure is known as reproductive specific crosses, while F 1 hybrids are viable and fully isolation. This reduction of fecundity of the hybrids fertile. Hybrid breakdown may be due to disruption prevents gene flow across the two different populations, of interaction of genes at different loci as the genes accelerating genetic differentiation and eventually consegregate after the F 1 generation. Assuming that two tributing to speciation. Thus, the study of reproductive diverging populations have different alleles at each of isolation is essential for understanding the process of two loci that genetically interact, it is inferred that the speciation.proper interaction may occur only in the allele combinaIn mice, genetic studies on reproductive isolation tions that occur in each of the two diverging populahave focused mostly on male sterility in F 1 hybrids betions. Hybrid breakdown is thus hypothesized to arise tween subspecies or closely related species. This hybrid when genetic segregation causes alleles of each intersterility is likely caused by interallelic incompatibility at acting locus to become homozygous in an improper way. a given locus or at several different loci. In such cases, Therefore, the hybrid breakdown appears as a recessive one allele or a set of alleles is fixed or predominates trait (Muller 1940; Orr 1993). Little is known about in each genetically differentiating population. Hybrid the gene...

Mutualisms are often viewed as reciprocal exploitations that nonetheless provide net benefits to each partner. While the benefits of symbiosis with dinoflagellates of the genus Symbiodinium (zooxanthellae) for corals are well understood, the costs of the association, particularly when under stress, remain a focus of much research. One of the primary impediments to exploring the costs of symbiosis in zooxanthellate corals is that it is impossible to examine the animal host in isolation. Evidence for a cost of symbiosis with zooxanthellae includes the fact that direct transmission of zooxanthellae between generations is rare, particularly in broadcast spawning corals. Fortuitously, the absence of zooxanthellae in oocytes of many species and the ability to readily infect larvae with zooxanthellae provide an opportunity to compare individuals with and without these symbionts. Here, we use this larval model to show that individuals with zooxanthellae have lower survival than those lacking zooxanthellae when exposed to high temperature. Higher activity of anti-oxidant defenses and higher levels of oxidative cellular damage in larvae with zooxanthellae suggest that oxidative stress originating in the symbionts is a cause of tissue damage in the host under heat stress. We hypothesize that this may be one reason for the absence of direct transmission of zooxanthellae in most broadcast spawning corals whose propagules must spend at least 1 d on the ocean surface.

Reproductive isolation that initiates speciation is likely caused by incompatibility among multiple loci in organisms belonging to genetically diverging populations. Laboratory C57BL/6J mice, which predominantly originated from Mus musculus domesticus, and a MSM/Ms strain derived from Japanese wild mice (M. m. molossinus, genetically close to M. m. musculus) are reproductively isolated. Their F 1 hybrids are fertile, but successive intercrosses result in sterility. A consomic strain, C57BL/6J-ChrX MSM , which carries the X chromosome of MSM/Ms in the C57BL/6J background, shows male sterility, suggesting a genetic incompatibility of the MSM/Ms X chromosome and other C57BL/6J chromosome(s). In this study, we conducted genomewide linkage analysis and subsequent QTL analysis using the sperm shape anomaly that is the major cause of the sterility of the C57BL/6J-ChrX MSM males. These analyses successfully detected significant QTL on chromosomes 1 and 11 that interact with the X chromosome. The introduction of MSM/Ms chromosomes 1 and 11 into the C57BL/6J-ChrX MSM background failed to restore the sperm-head shape, but did partially restore fertility. This result suggests that this genetic interaction may play a crucial role in the reproductive isolation between the two strains. A detailed analysis of the male sterility by intracytoplasmic sperm injection and zona-free in vitro fertilization demonstrated that the C57BL/6J-ChrX MSM spermatozoa have a defect in penetration through the zona pellucida of eggs.

We estimated open-loop dynamic characteristics of the carotid sinus baroreflex in normal control rats and chronic heart failure (CHF) rats after myocardial infarction. First, the neural arc transfer function from carotid sinus pressure to splanchnic sympathetic nerve activity (SNA) and its corresponding step response were examined. Although the steady-state response was attenuated in CHF, the negative peak response and the time to peak did not change significantly, suggesting preserved neural arc dynamic characteristics. Next, the peripheral arc transfer function from SNA to arterial pressure (AP) and its corresponding step response were examined. The steady-state response and the initial slope were reduced in CHF, suggesting impaired end-organ responses. In a simulation study based on the dynamic and static characteristics, the percent recovery of AP was reduced progressively as the size of disturbance increased in CHF, suggesting that a reserve for AP buffering is lost in CHF despite relatively maintained baseline AP.

These findings indicate that ocular complications of SDT rats are caused by hyperglycaemia. The features of SDT rats indicate their usefulness for the future study of diabetic retinopathy.

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Dysphagia occurs in acute stroke patients at high rates, and many of them develop aspiration pneumonia. Team approaches with the cooperation of various professionals have the power to improve the quality of medical care, utilizing the specialized knowledge and skills of each professional. In our hospital, a multidisciplinary participatory swallowing team was organized. The aim of this study was to clarify the influence of a team approach on dysphagia by comparing the rates of pneumonia in acute stroke patients prior to and post team organization. All consecutive acute stroke patients who were admitted to our hospital between April 2009 and March 2014 were registered. We analyzed the difference in the rate of pneumonia onset between the periods before team organization (prior period) and after team organization (post period). Univariate and multivariate analyses were performed using a Cox proportional hazards model to determine the predictors of pneumonia. We recruited 132 acute stroke patients from the prior period and 173 patients from the post period. Pneumonia onset was less frequent in the post period compared with the prior period (6.9% vs. 15.9%, respectively; p = 0.01). Based on a multivariate analysis using a Cox proportional hazards model, it was determined that a swallowing team approach was related to pneumonia onset independent from the National Institutes of Health Stroke Scale score on admission (adjusted hazard ratio 0.41, 95% confidence interval 0.19–0.84, p = 0.02). The multidisciplinary participatory swallowing team effectively decreased the pneumonia onset in acute stroke patients.