Nemaline myopathy is a hereditary disease of skeletal muscle defined by a distinct pathology of electron-dense accumulations within the sarcomeric units called rods, muscle weakness and, in most cases, a slow oxidative (type 1) fiber predominance. We generated a transgenic mouse model to study this disorder by expressing an autosomal dominant mutant of alpha-tropomyosin(slow) previously identified in a human cohort. Rods were found in all muscles, but to varying extents which did not correlate with the amount of mutant protein present. In addition, a pathological feature not commonly associated with this disorder, cytoplasmic bodies, was found in the mouse and subsequently identified in human samples. Muscle weakness is a major feature of this disease and was examined with respect to fiber composition, degree of rod-containing fibers, fiber mechanics and fiber diameter. Hypertrophy of fast, glycolytic (type 2B) fibers was apparent at 2 months of age. Muscle weakness was apparent in mice at 5-6 months of age, mimicking the late onset observed in humans with this mutation. The late onset did not correlate with observed changes in fiber type and rod pathology. Rather, the onset of muscle weakness correlates with an age-related decrease in fiber diameter and suggests that early onset is prevented by hypertrophy of fast, glycolytic fibers. We suggest that the clinical phenotype is precipitated by a failure of the hypertrophy to persist and therefore compensate for muscle weakness.

The aim of this study was to investigate the effect of leukaemia inhibitory factor (LIF) on human blastocyst formation rates in vitro. To do this, it was first necessary to devise a complex serum-free medium (CSFM) in which to test its activity. Blastocyst formation rates in CSFM microdrops (18.4%) showed no difference to those obtained previously for embryos cultured in 1 ml T6 medium containing 10% serum (25%). The majority of blastocysts were of optimal blastocyst grade (BG1/BG2) as compared to the poor grade (BG3). The percentage of BG1/BG2 blastocysts was decreased in CSFM microdrops (10.2%) compared to that observed in T6 medium (24.8%). Addition of 1000 IU/ml LIF to CSFM microdrops increased the blastocyst formation rate from 18.4 to 43.6% (P = 0.025) and increased the percentage of BG1/BG2 blastocysts (33%; P = 0.025) to levels comparable with those observed in T6 medium. Thus LIF significantly increased the quality and number of human blastocysts formed in CSFM medium, increasing the potential for blastocyst transfer in human in-vitro fertilization (IVF).

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