Differential requirements for Myocyte Enhancer Factor-2 during adult myogenesis in Drosophila.

Identifying the genetic program that leads to formation of functionally and morphologically distinct muscle fibers is one of the major challenges in developmental biology. In Drosophila, the Myocyte Enhancer Factor-2 (MEF2) transcription factor is important for all types of embryonic muscle differentiation. In this study we investigated the role of MEF2 at different stages of adult skeletal muscle formation, where a diverse group of specialized muscles arises. Through stage- and tissue-specific expression of Mef2 RNAi constructs, we demonstrate that MEF2 is critical at the early stages of adult myoblast fusion: mutant myoblasts are attracted normally to their founder cell targets, but are unable to fuse to form myotubes. Interestingly, ablation of Mef2 expression at later stages of development showed MEF2 to be more dispensable for structural gene expression: after myoblast fusion, Mef2 knockdown did not interrupt expression of major structural gene transcripts, and myofibrils were formed. However, the MEF2-depleted fibers showed impaired integrity and a lack of fibrillar organization. When Mef2 RNAi was induced in muscles following eclosion, we found no adverse effects of attenuating Mef2 function. We conclude that in the context of adult myogenesis, MEF2 remains an essential factor, participating in control of myoblast fusion, and myofibrillogenesis in developing myotubes. However, MEF2 does not show a major requirement in the maintenance of muscle structural gene expression. Our findings point to the importance of a diversity of regulatory factors that are required for the formation and function of the distinct muscle fibers found in animals.

Human papillomavirus genotype-specific prevalence across the continuum of cervical neoplasia and cancer.

BACKGROUND: The New Mexico HPV Pap Registry was established to measure the impact of cervical cancer prevention strategies in the United States. Before widespread human papillomavirus (HPV) vaccine implementation, we established the baseline prevalence for a broad spectrum of HPV genotypes across the continuum of cervical intraepithelial neoplasia (CIN) and cancer. METHODS: A population-based sample of 6,272 tissue specimens was tested for 37 HPV genotypes. The number of specimens tested within each diagnostic category was: 541 negative, 1,411 CIN grade 1 (CIN1), 2,226 CIN grade 2 (CIN2), and 2,094 CIN grade 3 (CIN3) or greater. Age-specific HPV prevalence was estimated within categories for HPV genotypes targeted by HPV vaccines. RESULTS: The combined prevalence of HPV genotypes included in the quadrivalent and nonavalent vaccines increased from 15.3% and 29.3% in CIN1 to 58.4% and 83.7% in CIN3, respectively. Prevalence of HPV types included in both vaccines tended to decrease with increasing age for CIN1, CIN2, CIN3, and squamous cell carcinoma (SCC), most notably for CIN3 and SCC. The six most common HPV types in descending order of prevalence were HPV-16, -31, -52, -58, -33, and -39 for CIN3 and HPV-16, -18, -31, -45, -52, and -33 for invasive cancers. CONCLUSIONS: Health economic modeling of HPV vaccine impact should consider age-specific differences in HPV prevalence. IMPACT: Population-based HPV prevalence in CIN is not well described, but is requisite for longitudinal assessment of vaccine impact and to understand the effectiveness and performance of various cervical screening strategies in vaccinated and unvaccinated women.

The Drosophila wings apart gene anchors a novel, evolutionarily conserved pathway of neuromuscular development.

wings apart (wap) is a recessive, semilethal gene located on the X chromosome in Drosophila melanogaster, which is required for normal wing-vein patterning. We show that the wap mutation also results in loss of the adult jump muscle. We use complementation mapping and gene-specific RNA interference to localize the wap locus to the proximal X chromosome. We identify the annotated gene CG14614 as the gene affected by the wap mutation, since one wap allele contains a non-sense mutation in CG14614, and a genomic fragment containing only CG14614 rescues the jump-muscle phenotypes of two wap mutant alleles. The wap gene lies centromere-proximal to touch-insensitive larva B and centromere-distal to CG14619, which is tentatively assigned as the gene affected in introverted mutants. In mutant wap animals, founder cell precursors for the jump muscle are specified early in development, but are later lost. Through tissue-specific knockdowns, we demonstrate that wap function is required in both the musculature and the nervous system for normal jump-muscle formation. wap/CG14614 is homologous to vertebrate wdr68, DDB1 and CUL4 associated factor 7, which also are expressed in neuromuscular tissues. Thus, our findings provide insight into mechanisms of neuromuscular development in higher animals and facilitate the understanding of neuromuscular diseases that may result from mis-expression of muscle-specific or neuron-specific genes.

Crossveinless and the TGFbeta pathway regulate fiber number in the Drosophila adult jump muscle.

Skeletal muscles are readily characterized by their location within the body and by the number and composition of their constituent muscle fibers. Here, we characterize a mutation that causes a severe reduction in the number of fibers comprising the tergal depressor of the trochanter muscle (TDT, or jump muscle), which functions in the escape response of the Drosophila adult. The wild-type TDT comprises over 20 large muscle fibers and four small fibers. In crossveinless (cv) mutants, the number of large fibers is reduced by 50%, and the number of small fibers is also occasionally reduced. This reduction in fiber number arises from a reduction in the number of founder cells contributing to the TDT at the early pupal stage. Given the role of cv in TGFbeta signaling, we determined whether this pathway directly impacts TDT development. Indeed, gain- and loss-of-function manipulations in the TGFbeta pathway resulted in dramatic increases and decreases, respectively, in TDT fiber number. By identifying the origins of the TDT muscle, from founder cells specified in the mesothoracic leg imaginal disc, we also demonstrate that the TGFbeta pathway directly impacts the specification of founder cells for the jump muscle. Our studies define a new role for the TGFbeta pathway in the control of specific skeletal muscle characteristics.