Mechanisms regulating the maintenance of a mature skeletal musculature
Zusammenfassung der Projektergebnisse
We have used a multidisciplinary approach to characterize the function of two important regulators, mib2 and abba, in maintaining muscle integrity. First, we performed a structurefunction analysis to gain clues about the mechanistic aspects underlying Mib2 function. We identified at least two essential domains for Mib2 function during embryogenesis, the previously uncharacterized “MIB” domain and the Ankyrin repeats. The importance of these two domains is consistent with the function of Mib2 as an adapter-type of protein. A potential third domain that is associated with ubiquitination, HERC2, needs further testing. Second, we undertook a detailed analysis of Abba, a new member of the TRIM/RBCC superfamily. We determined that the formation of muscles is not affected in abba mutant embryos, but the mutant muscles become atrophied, exhibiting a dramatic disruption of F- actin and Myosin striations, as well as an abnormal accumulation of Myosin and positioning of the myonuclei. The defects are exascerbated during larval muscle growth, as well as when the muscles are subjected to increased contractile forces. Notably, the larval defects result in compromised muscle function such that important morphogenetic events do not occur properly during pupation, leading to early pupal lethality. We localized Abba protein to the Z-discs in larval muscles. Consistent with the protein localization data, our genetic findings further indicated that abba interacts with α-actinin, kettin/D-titin and mlp84B, genes encoding important Z-disc proteins for stable myofibrillar organization and optimal muscle function. Consequently, we concluded that Abba has a crucial regulatory role in maintaining proper sarcomeric cytoarchitecture during larval muscle development and usage. Third, we used standard and conditional RNAi strategies for assessing the role of abba and mib2 in adult muscle development. Ultrastructural analysis and flight tests revealed that Abba has an additional crucial role in maintaining the integrity of Z-discs and M-lines, as well as flying capabilities. A structure-function analysis further demonstrated that Abba function is dependent upon each of its recognizable domains, namely the B-box and coiled-coil domain, RING fingers, and NHL repeats. The importance of these domains, which are often associated with protein–protein interactions and ubiquitin ligase activity, is consistent with the notion that Abba is needed for complex formation and/or turnover of sarcomeric components, as well as for structural stabilization of Z-discs and M-lines in adult muscles. In addition to Abba, we found that Mib2 is also important for the formation of adult muscles. A specific loss of the dorso-longitudinal muscles within the thorax was observed when mib2 function was reduced.
Projektbezogene Publikationen (Auswahl)
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(2013) Abba is an essential TRIM/RBCC protein to maintain the integrity of sarcomeric cytoarchitecture. Journal of Cell Science 126, 3314–3323
Domsch, K., Ezzeddine, N., and Nguyen, H.T.
