The muscle weakness phenotype of the Mariusz mutant.

<p>(<b>A</b>) The original pedigree in which the Mariusz mutant was identified. (<b>B</b>) Grip-strength comparison using 3-month-old Mariusz homozygotes (n = 30) and wild type (n = 26) littermate controls. The average force generated by wild type mice has been set as 100%. Mean and SD are shown. The differences are highly significant; P-values (Student's t test): *** <i>P</i><0.0001. (<b>C</b>) Close-up photos showing the different grasp of Mariusz homozygotes (<i>Mz/Mz</i>) and wild type littermate controls. (<b>D</b>) Example of clasping phenotype observed in a Mariusz homozygote and littermate control. (<b>E</b>) A wire manoeuvre test of Mariusz mice and littermate controls. Scores are as follows: 0 = mouse swings hindlegs on to bar and makes way to edge rapidly; 1 = mouse swings hindlegs on to bar after a delay and makes way to edge rapidly; 2 = mouse is suspended by using underarms to straddle bar and does not lift hind limbs, eventually falls; 3 = mouse falls after short delay; 4 = mouse falls immediately.</p

Muscle force measurements in Mariusz mice.

<p>(<b>A</b>) Morphometric measurement of cross-sectional area of Mariusz muscles in histological sections normalized to the area of the muscle in wild type controls (n = 3 mice each genotype at 5 weeks of age; n = 50 fibres counted per sample). Muscle abbreviations are: FDS, Flexor Digitorum Sublimis; FCR, Flexor Carpi Radialis; ECU, Extensor Carpi Ulnaris; ECR, Extensor Carpi Radialis. ‘Area forelimb’ refers to the entire area of the forelimb to emphasize the size difference between Mariusz mice and littermates controls. (<b>B</b>) Example trace of a tetanic contraction in a Mariusz soleus muscle and a wild type control. (<b>C</b>) Mean peak tetanic force for control (n = 5) and Mariusz (n = 6) mice with SEM shown by error bars. (<b>D</b>) Mean isometric stress of the soleus muscle for wild type (n = 5) and Mariusz (n = 6) mice with SEM shown by error bars. (<b>E</b>) The mean ratio of the mass of the soleus muscle to the mass of the mouse for control (n = 5) and Mariusz (n = 6) mice with SEM shown by error bars. (<b>F</b>) The mean maximum contraction velocity of the soleus muscle in wild type control (n = 4) and Mariusz (n = 5) mice with SEM shown by error bars. P-values: * <i>P</i><0.05; ** <i>P</i><0.01.</p

The digit fusion phenotype of the Mariusz mutant.

<p>(<b>A</b>) Examples of different fusion phenotypes observed - four toes (#1), four toes with two toes fused (#2), four toes with skewed digit (#3), mixture of two digit phenotypes in a single mouse (#4). (<b>B</b>) Hard and soft tissue fusion seen in Mariusz mice. Alcian Blue/Alizarin Red-stained left hindlimbs of P7 mice showing a littermate heterozygous control (left), soft tissue syndactyly of toes 3 and 4 (centre), and syndactyly of toes 2,3 and 4 with fusion of the distal phalanges (right). (<b>C</b>) X-ray analysis of a hindlimb of a Mariusz mutant demonstrating fusion of the soft tissue as well as the distal phalanx bones. (<b>D</b>) Morag test on Mariusz mice and wild type littermates. The proportion of trials in which the mice were able to grasp the food pellets and retrieve the pellets to their mouths are shown. (<b>E</b>) Mariusz mice have a reduced body weight. Growth curves of Mariusz male mice and littermate controls. Picture shows a typical example of the size difference between an adult Mariusz female mouse and a littermate control at 3 months of age.</p

Skeletal muscle histology in Mariusz mice.

<p>(<b>A</b>) Morphometric analysis of muscle fibre cross-sectional area in the soleus and quadriceps muscles in Mariusz (n = 3) and wild type controls (n = 3). Two-way ANOVA was not significant. (<b>B</b>) Typical H&E sections of Mariusz quadriceps muscle from mice at 4 and 9 weeks of age. Scale bar = 100 um. (<b>C</b>) Quantification of central nucleation. The number of muscle fibres with central nuclei is represented as percentage of the total number of muscle fibres analyzed in >100 fibres. Arrows indicate centrally displaced nuclei. Mice were aged 4 weeks and 9 weeks (n = 3 <i>Mz/Mz</i>; n = 3<i>+/+</i>). P-values (Student's t test): * <i>P</i><0.05, ** <i>P</i><0.01.</p

Genetic linkage analysis and positional cloning of the <i>Mz</i> mutation.

<p>(<b>A</b>) Genotypes of seven informative recombinants exhibiting the Mariusz phenotype. The mutation was localized to a 2.5 Mb interval (indicated by the bracketed region). (<b>B</b>) Sequence of part of exon 14 of the <i>Fbn2</i> gene reveals a T-A substitution in the Mariusz allele. The reading frame of part of exon 14 is shown with the amino acid substitution that results. (<b>C</b>) Schematic of the Fbn2 wild type protein and the truncation that results from the Mariusz mutation.</p