ABSTRACT
The Drosophila gene Dm nxf1 (nuclear export factor 1) previously known as small bristles (sbr) controls nuclear export of various mRNA transcripts. We found that Dm NXF1 is present not only in nucleoplasm or at the nuclear rim but also in the cytoplasm. On the spatiotemporal level, anti-SBR antibodies labeled some neuroblasts and their lineages in the brains of Drosophila larvae. The number of Dm NXF1-rich lineages increased during larval development, but Dm NXF1 expression was not evident in all lineages. In all larval stages, Dm NXF1 concentrated in the midline cells of the ventral nerve cord, which reflects a specific status of those cells. In neurites, Dm NXF1 was present in the form of cytoplasmic granules, which is similar to the behavior of another RNA-binding protein, dFMR. Interestingly, though, the granule expression pattern of Dm NXF1 and dFMR did not always overlap, as some granules stained exclusively for one or the other protein. It suggests the existence of specific mRNA partners for Dm NXF1 in neurites.
Subject(s)
Cytoplasm/metabolism , Drosophila Proteins/metabolism , Ganglia, Invertebrate/metabolism , Nuclear Proteins/metabolism , RNA-Binding Proteins/metabolism , Animals , Cytoplasm/chemistry , Drosophila melanogaster , LarvaABSTRACT
The tissue-specific accumulation of small bristles (Dm nxf1) transcripts at different developmental stages of Drosophila melanogaster was analyzed by Northern blots and RT PCR. We identified four distinct transcripts: ubiquitous (3.5kb); ovary and early embryo specific (3.3kb); testis specific (1.9kb and 2.8kb) and nervous system specific (5.1kb). The pattern of Dm nxf1 gene expression in ovaries and early embryos (0-2h) is similar: the sizes of transcripts range from 3.0 to 3.5kb. We propose that this size variability may reflect the different extent of cytoplasmic polyadenylation. In testes, the 2.8-kb transcript originates from alternative termination of transcription and the 1.9-kb transcript is supposed to originate from an alternative transcription start. During ontogenesis, the 5.1-kb transcript can be clearly detected in 10- to 18-h-old embryos, most prominently in the nervous ganglia of larvae, and it represents a major species in imago head extracts. We found that the 5.1-kb transcript, similarly to the nxf1 heavy transcripts in Homo sapiens and Mus musculus, results from the retention of intron 5-6 that corresponds to the intron 10-11 in Hs nxf1 and Mm nxf1 genes.
Subject(s)
Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Gene Expression , Nuclear Proteins/genetics , RNA-Binding Proteins/genetics , Animals , Base Sequence , Blotting, Northern , Drosophila Proteins/metabolism , Drosophila melanogaster/embryology , Drosophila melanogaster/metabolism , Embryo, Nonmammalian/metabolism , Female , Introns , Male , Molecular Sequence Data , Nuclear Proteins/metabolism , Ovary/embryology , RNA-Binding Proteins/metabolism , Sequence Alignment , Testis/embryologyABSTRACT
The small bristles (sbr) gene of Drosophila melanogaster belongs to the family of nuclear export factor (NXF) genes that participate in mRNA nuclear export. During meiosis, females of Drosophila melanogaster that carry various combinations of mutant alleles of the Dm nxf1/sbr gene exhibit disruption of the division spindle and misalignment of chromosomes at the metaphase plate. Meiosis of sbr ( 5 ) /+ females is characterized by the formation of tripolar spindles during the first cell division. According to the sequencing results, the sbr ( 5 ) (l(1)K4) lethal allele is a deletion of 492 nucleotides. In SBR(5) protein, 57 of the 146 amino acids that have been lost by deletion belong to the NTF2-like domain.
