Molecular genetic characterization of novel alleles of fldB, a gene involved in muscle structure and function. N.W. O'Brien , J. Bacalski , L. Morrison , G.L. Harris. Molecular Biology Institute, San Diego State University, San Diego, CA.

   We are using molecular genetic approaches to characterize genes involved in skeletal muscle structure and function. AD170 is a P-lwb enhancer trap line that appears to have no phenotype, but which expresses the lacZ reporter gene in cells of the indirect flight muscles (IFM). This line was previously used to generate mutations in fldB , a novel gene that appears to be involved in proper muscle assembly and function (O'Brien, 1999)¹. Using both local hop (LH) and excision (E) strategies, AD170 was again used in a P element mutagenesis screen in an effort to acquire additional alleles of this gene. The screen generated three recessive flightless mutants (LH80a, LH77c, and E71c), and one recessive lethal mutant (LH16a). Complementation analysis, along with preliminary sequence analysis of isolated plasmid rescue fragments, suggests these are indeed novel alleles of fldB. Ultrastructural analysis of the IFMs from these mutants reveals a similar disruption of the myofibrils, as exhibited by incompletely formed, missing, or skewed Z disks, an irregular array of myofilaments, ill-defined sarcomeres and misshapened myofibrils. Northern analysis of the fldB transcript shows a size of approximately 4 kb, and a partial cDNA of 1.4 kb has been isolated, which seems to contain no significant homology to other known genes. Currently, work is in progress to further characterize this gene and its alleles. (Supported by the MDA.)
   ¹N.W. O'Brien, J. Mendy, L. Morrison, and G.L. Harris. Molecular genetic characterization of a novel gene involved in muscle structure and function. A. Conf. Dros. Res. 40: 398A, 1999.