[PDF] Genetic Analysis Of Myosin Light Chain 2 Function In Drosophila Melanogaster eBook

Author : Deyra Marie Rodriguez
Publisher :
Page : pages
File Size : 13,82 MB
Release : 2004
Category : Actin
ISBN :

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Abstract: Muscle function depends upon the molecular interaction of myosin and actin. This interaction and the function of each molecule are tightly regulated and have been extensively studied. In Drosophila, the indirect flight musculature (IFM) is a powerful model to study muscle structure and function as these muscles are dispensable for life under laboratory conditions. Furthermore, disruption of these muscles leads to a flightless behavior. Flies with mutations in the muscle regulatory light chain (MLC2) that cannot be phosphorylated at the conserved Myosin light chain kinase (Mlck) target sites are flightless, but the IFM is normal. Flight impairment is due to an altered stretch activation response, thus phosphorylation of MLC2 at the Mlck target sites is important for flight. In Drosophila, the Stretchin-Mlck (Strn-Mlck) gene encodes several Mlck-like isoforms with kinase activity as well as other isoforms lacking this domain. This work has shown that the gene is expressed in both muscle and nonmuscle cells and that some isoforms show tissue specific expression patterns. In order to understand what role Strn-Mlck plays in MLC2 regulation, mutants were isolated. Three new mutants were identified and were shown to be new alleles of the previously identified mutant curved . Strikingly, Strn-Mlck mutants lacking kinase activity are viable. However, the mutants show a recessive flightless phenotype and defects in wing position. Electron micrographs demonstrated the flight musculature is intact, therefore, the flightless phenotype is most likely due to the wing position defect. As mentioned, Strn-Mlck is expressed in nonmuscle cells. The myosin nonmuscle regulatory light chain is encoded by spaghetti squash (sqh) . Mutations in nonmuscle RLC at the conserved Mlck target sites are lethal. Finding that mutants lacking Strn-Mlck kinase activity are viable suggests other Mlcks exist in flies and function redundantly. Preliminary genetic studies have linked Strn-Mlck with another Mlck, CG1776 (also known as Mlck-2). This Mlck-like kinase has been implicated in morphogenesis in nonmuscle tissue culture cells. In the future, it will be important to analyze these two Mlcks in depth at the genetic level. Double mutants may reveal functions for these enzymes that are masked in the single mutants analyzed to date.

Author : Becky Marlene Miller
Publisher :
Page : 336 pages
File Size : 17,5 MB
Release : 2004
Category : Drosophila melanogaster
ISBN :

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Drosophila melanogaster has a single myosin alkali light chain gene which encodes for two protein isoforms by developmentally regulated alternative splicing of the primary transcript. All six of the exons in the gene are present in the mRNA of larval muscles and the tubular and abdominal muscles of the adults. A novel mRNA species present exclusively in the adult and pupal Indirect Flight Muscle (IFM) lacks the fifth exon, thus encoding a MLC-ALK isoform with a variant carboxyl terminus. All introns of the transcript contain the established concensus splicing signals with the exception of intron 4. In this intron, a non-canonical polypurine stretch replaces the concensus polypyrimidine, rendering it a likely regulatory site. Because the transcripts are colinear with the gene throughout development the alternative splicing pattern in the IFM appears to be regulated at the level of splice site choice. The goal of this research is to identify the cis-regulatory sequences that control the choice between alternative larval and IFM-specific splicing pathways. I have developed a transient expression system for Drosophila Schneider 2 cultured cells utilizing the Drosophila metallothionein promoter to direct transcription of transfected MLC-ALK minigenes. This analysis demonstrated that the larval-specific splicing pathway represents the default splicing of the MLC-ALK transcripts. Analysis of mutant minigene transcripts revealed that splicing in the IFM-specific pathway is not the result of blockage or incapacitation of either splice acceptor or/and donor sequences flanking exon 5. The structures of the mutant mRNAs suggest that utilization of the IFM-specific pathway requires trans-acting factors which are absent in the cultured cells. Furthermore, analysis of mutant and hybrid minigene transcripts identified a unique cis-regulatory sequence proximal to the splice donor of intron 4, required for efficient utilization of the larval-specific splicing pathway. Mutations in intron 4 inhibit removal of the downstream intron 5 suggesting that an ordered pathway of intron removal is employed for larval-specific splicing. On the basis of these results a model of the mechanism of tissue and temporal regulation of alternative splicing of the MLC-ALK transcripts is presented.

Author : Madhulika Achal
Publisher :
Page : 39 pages
File Size : 46,52 MB
Release : 2012
Category :
ISBN :

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Myosin, a motor protein, is composed of two heavy chains and four light chains. It hydrolyzes ATP to generate actin-based motility and the contractile force in muscles. A mutation in human cardiac beta myosin heavy chain that changes amino acid residue 838 from proline to leucine (P838L) results in pediatric restrictive cardiomyopathy. Restrictive cardiomyopathy (RCM) leads to rigidity of the ventricular wall and the heart is restricted from stretching and properly filling with blood. Therefore, blood flow is reduced and blood that would normally enter the heart is backed up in the circulatory system. Gradually, the patient loses the ability to pump blood efficiently, leading to heart failure. Drosophila has a rhythmically beating heart and serves as a powerful tool to study the genetic basis of heart development and disease in humans. To define the biochemical basis of myosin-based RCM and to test the hypothesis that the P838L mutation causes RCM in Drosophila, a gene encoding myosin with the P838L mutation was constructed and was expressed in place of wild-type myosin heavy chain by P element transformation. Jump tests indicated that the mutation did not have any effect on the jump muscles. However reduced flight ability was observed, indicating impairment in the indirect flight muscle expressing this mutant myosin. ATPase assays and in vitro motility assays were performed to determine the effect of the mutation at the molecular level. We found that there was a slight increase in the actin-sliding velocity and that the basal and actin-activated MgATPase activity was significantly higher for the mutants. Electron microscopy on 2 day-old mutants and the controls suggested that the myofibrils were intact but some of them were oblong in shape and had rough edges when compared to the control myofibrils. Preliminary video microscopy data suggest that the transgenic hearts display a restrictive phenotype. The P838L mutation affects an "invariant proline" located at the junction of the myosin S1 head and the S2 rod and might affect the movement of the myosin heads during the force generation step. This could lead to the observed increase in the ATPase rate. Also, the P838L mutation is located near to where the regulatory light chain (RLC) binds to the heavy chain. RLC has an important role in the ATPase cycle and the P838L mutation might alter the RLC conformation leading to the increased ATPase rate. The increased ATPase rate seen in this and another Drosophila myosin that causes a restrictive phenotype may initiate a cascade of events that result in the observed cardiac defects.

Author : Dipak K. Dube
Publisher : Springer Science & Business Media
Page : 304 pages
File Size : 19,5 MB
Release : 2001-10-19
Category : Science
ISBN : 9780817642266

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Myofibrillogenesis has been studied extensively over the last 100 years. Until recently, we have not had a comprehensive understanding of this fundamental process. The emergence of new technologies in molecular and cellular biology, combined with classical embryology, have started to unravel some of the complexities of myofibril assembly in striated muscles. In striated muscles, the contractile proteins are arranged in a highly ordered three dimensional lattice known as the sarcomere. The assembly of a myofibril involves the precise ordering of several proteins into a linear array of sarcomeres. Multiple isoforms in many of these proteins further complicate the process, making it difficult to define the precise role of each component. This volume has been compiled as a comprehensive reference on myofibrillogenesis. In addition, the book includes reviews on myofibrillar disarray under various pathological conditions, such as familial hypertrophic cardiomyopathy (FHC), and incorporates a section on the conduction system in the heart. Much of the information in this volume has not been described elsewhere. Presented in a manner to be of value to students and teachers alike, "Myofibrillogenesis" will be an invaluable reference source for all in the fields of muscle biology and heart development.

Author : Josh Dubnau
Publisher : Cambridge University Press
Page : 309 pages
File Size : 40,94 MB
Release : 2014-06-26
Category : Medical
ISBN : 1107009030

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A comprehensive portrayal of the behaviour genetics of the fruit fly (Drosophila melanogaster) and the methods used in these studies.