RESUMEN
Tubular networks like the vasculature extend branches throughout animal bodies, but how developing vessels interact with and invade tissues is not well understood. We investigated the underlying mechanisms using the developing tracheal tube network of Drosophila indirect flight muscles (IFMs) as a model. Live imaging revealed that tracheal sprouts invade IFMs directionally with growth-cone-like structures at branch tips. Ramification inside IFMs proceeds until tracheal branches fill the myotube. However, individual tracheal cells occupy largely separate territories, possibly mediated by cell-cell repulsion. Matrix metalloproteinase 1 (MMP1) is required in tracheal cells for normal invasion speed and for the dynamic organization of growth-cone-like branch tips. MMP1 remodels the CollagenIV-containing matrix around branch tips, which show differential matrix composition with low CollagenIV levels, while Laminin is present along tracheal branches. Thus, tracheal-derived MMP1 sustains branch invasion by modulating the dynamic behavior of sprouting branches as well as properties of the surrounding matrix.
Asunto(s)
Drosophila/embriología , Drosophila/enzimología , Metaloproteinasa 1 de la Matriz/metabolismo , Músculos/embriología , Tráquea/embriología , Animales , Colágeno Tipo IV/metabolismo , Laminina/metabolismoRESUMEN
Morphogenesis requires the dynamic regulation of gene expression, including transcription, mRNA maturation and translation. Dysfunction of the general mRNA splicing machinery can cause surprisingly specific cellular phenotypes, but the basis for these effects is not clear. Here, we show that the Drosophila faint sausage (fas) locus, which is implicated in epithelial morphogenesis and has previously been reported to encode a secreted immunoglobulin domain protein, in fact encodes a subunit of the spliceosome-activating Prp19 complex, which is essential for efficient pre-mRNA splicing. Loss of zygotic fas function globally impairs the efficiency of splicing, and is associated with widespread retention of introns in mRNAs and dramatic changes in gene expression. Surprisingly, despite these general effects, zygotic fas mutants show specific defects in tracheal cell migration during mid-embryogenesis when maternally supplied splicing factors have declined. We propose that tracheal branching, which relies on dynamic changes in gene expression, is particularly sensitive for efficient spliceosome function. Our results reveal an entry point to study requirements of the splicing machinery during organogenesis and provide a better understanding of disease phenotypes associated with mutations in general splicing factors.
Asunto(s)
Proteínas de Drosophila/metabolismo , Proteínas de Drosophila/fisiología , Drosophila melanogaster/embriología , Neuropéptidos/metabolismo , Factores de Empalme de ARN/metabolismo , Empalme del ARN , Tráquea/embriología , Alelos , Animales , Movimiento Celular , Drosophila melanogaster/metabolismo , Desarrollo Embrionario , Femenino , Regulación del Desarrollo de la Expresión Génica , Inmunoglobulinas/metabolismo , Intrones , Masculino , Morfogénesis , Mutación , Precursores del ARN/genética , Factores de Empalme de ARN/fisiología , ARN Mensajero/metabolismo , Empalmosomas/metabolismo , Tráquea/metabolismoRESUMEN
Inherited mtDNA mutations cause severe human disease. In most species, mitochondria are inherited maternally through mechanisms that are poorly understood. Genes that specifically control the inheritance of mitochondria in the germline are unknown. Here, we show that the long isoform of the protein Oskar regulates the maternal inheritance of mitochondria in Drosophila melanogaster. We show that, during oogenesis, mitochondria accumulate at the oocyte posterior, concurrent with the bulk streaming and churning of the oocyte cytoplasm. Long Oskar traps and maintains mitochondria at the posterior at the site of primordial germ cell (PGC) formation through an actin-dependent mechanism. Mutating long oskar strongly reduces the number of mtDNA molecules inherited by PGCs. Therefore, Long Oskar ensures germline transmission of mitochondria to the next generation. These results provide molecular insight into how mitochondria are passed from mother to offspring, as well as how they are positioned and asymmetrically partitioned within polarized cells.
Asunto(s)
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Genes de Insecto , Genes Mitocondriales/genética , Actinas/metabolismo , Animales , Variaciones en el Número de Copia de ADN , ADN Mitocondrial/genética , ADN Mitocondrial/metabolismo , Drosophila melanogaster/embriología , Drosophila melanogaster/metabolismo , Células Germinales Embrionarias/metabolismo , Femenino , Humanos , Oogénesis/genética , Isoformas de Proteínas/genéticaRESUMEN
A special group of mitochondrial outer membrane (MOM) proteins spans the membrane several times via multiple helical segments. Such multispan proteins are synthesized on cytosolic ribosomes before their targeting to mitochondria and insertion into the MOM. Previous work recognized the import receptor Tom70 and the mitochondrial import (MIM) complex, both residents of the MOM, as required for optimal biogenesis of these proteins. However, their involvement is not sufficient to explain either the entire import pathway or its regulation. To identify additional factors that are involved in the biogenesis of MOM multispan proteins, we performed complementary high-throughput visual and growth screens in Saccharomyces cerevisiae. Cardiolipin (CL) synthase (Crd1) appeared as a candidate in both screens. Our results indeed demonstrate lower steady-state levels of the multispan proteins Ugo1, Scm4, and Om14 in mitochondria from crd1Δ cells. Importantly, MOM single-span proteins were not affected by this mutation. Furthermore, organelles lacking Crd1 had a lower in vitro capacity to import newly synthesized Ugo1 and Scm4 molecules. Crd1, which is located in the mitochondrial inner membrane, condenses phosphatidylglycerol together with CDP-diacylglycerol to obtain de novo synthesized CL molecules. Hence, our findings suggest that CL is an important component in the biogenesis of MOM multispan proteins.