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M Akam

Publications and source records attributed to M Akam.

13 recordsLinked to original sources
PubMed1992

Oligonucleotide probes detect splicing variants in situ in Drosophila embryos.

We describe a method for the in situ detection of specific splicing variants. The method is based on the use of antisense oligonucleotides designed to span splice junctions labelled with digoxigenin by terminal transferase tailing. We find that the spatial patterns of Ubx splicing variants Ia and IIa are similar in early embryos, but differ in late embryos. Variant IVa is only detected in the CNS (ps6) at stages 16 and 17. We also present evidence indicating that the first splicing event is cotranscriptional.

Alternative Splicing↗
PubMed1990

Isolation of an abdominal-A gene from the locust Schistocerca gregaria and its expression during early embryogenesis.

Using sequence homology to Drosophila homeobox-containing genes, we have cloned a homologue of abdominal-A from the locust Schistocerca gregaria. The Schistocerca clone encodes a stretch of 78 amino acids including the homeodomain and its flanking regions identical to the corresponding region of abdominal-A. We have shown by in situ hybridization that this gene is transcribed and have used an antibody raised against its protein product to examine the expression of abdominal-A during early Schistocerca embryogenesis. Schistocerca is a short germ insect. Although the segmented body plan is very similar to that of Drosophila, the segments are generated sequentially by a process of growth, not simultaneously by subdivision of a syncytial blastoderm. In both organisms, abdominal-A is expressed throughout the abdomen from a sharp anterior boundary located within the first abdominal segment (A1). The initial activation of the genes in the two species differs. Schistocerca initiates expression in a small group of cells in the anterior of A2, shortly after this segment is defined by the appearance of engrailed protein. This contrasts with the appearance of abdominal-A expression in Drosophila, which appears simultaneously throughout the entire abdomen.

Amino Acid Sequence↗
PubMed1989

The Drosophila posterior-group gene nanos functions by repressing hunchback activity.

The development of the body plan in the Drosophila embryo depends on the activity of maternal determinants localized at the anterior and posterior of the egg. These activities define both the polarity of the anterior-posterior (AP) axis and the spatial domains of expression of the zygotic gap genes, which in turn control the subsequent steps in segmentation. The nature and mode of action of one anterior determinant, the bicoid(bcd) gene product, has recently been defined, but the posterior determinants are less well characterized. At least seven maternally acting genes are required for posterior development. Mutations in these maternal posterior-group genes result in embryos lacking all abdominal segments. Cytoplasmic transplantation studies indicate that the maternally encoded product of the nanos(nos) gene may act as an abdominal determinant, whereas the other maternal posterior-group genes appear to be required for the appropriate localization and stabilization of this signal. Here we show that the lack of the nos gene product can be compensated for by eliminating the maternal activity of the gap gene hunchback (hb). Embryos lacking both of these maternally derived gene products are viable and can survive as fertile adults. These results suggest that the nos gene product functions by repressing the activity of the maternal hb products in the posterior of the egg.

Abdomen↗
PubMed1989

Spatial regulation of the Antennapedia and Ultrabithorax homeotic genes during Drosophila early development.

Both maternally supplied products and zygotically acting segmentation genes are required to establish the segment pattern of the Drosophila embryo. These genes are thought to act in part by regulating the expression of the homeotic genes. Products of the maternal and zygotic gap genes are present in the egg prior to blastoderm formation, when the homeotic genes are initially expressed within precisely bounded domains. In order to assess the first regulatory interactions between some of these gap gene products and the homeotic genes, we have examined the spatial distribution of transcripts arising from the homeotic Antp and Ubx genes during early embryogenesis in various mutant backgrounds. Here we show that mutations in both maternally and zygotically acting gap genes differentially affect the initial spatial domains of transcripts arising from each of these homeotic gene promoters. Later in embryogenesis, the patterns of homeotic gene expression change in both the wild-type and mutant cases, suggesting that other regulatory activities come into play. We propose a model in which the initial activation of each homeotic gene promoter depends on a unique combination of gap and pair-rule gene activities.

Animals↗
PubMed1989

Spatially ordered transcription of regulatory DNA in the bithorax complex of Drosophila.

The identities of the second through ninth abdominal segments of Drosophila are specified by two genes of the bithorax complex (BX-C), abdominal-A (abd-A) and Abdominal B (Abd-B). The correct deployment of these two genes requires an extensive region (the iab region) located between the two protein-coding transcription units. We show here that one iab mutation affects the pattern of expression of Abd-B. We also show that most or all of the DNA in this regulatory iab region is transcribed. In blastoderm stage embryos we can define three distinct domains within the iab DNA, each transcribed in a region that extends from a characteristic anterior limit to the posterior end of the segmented part of the embryo. The anterior limits of expression for the three regions are colinear with the sequence of the domains on the chromosome, and lie at about two-segment intervals. We suggest that these early transcription patterns reflect the initial activation of the BX-C.

Animals↗
PubMed1988

A genetic analysis of the rose-gespleten region (68C8-69B5) of Drosophila melanogaster.

We describe a genetic analysis of the region 68C8-69B5 defined by Df(3L)vin-7. We have induced 35 new lethal mutations in this region, which together with 20 existing lethal mutations, visible mutations, genes identified by protein products and one gene deduced from complementation data fall into 37 complementation groups in this 35-band interval. Using existing and newly induced deficiencies we have assigned these to 11 intervals defined by deficiency breakpoints. Those mutations which fell in the same breakpoint interval as the Lsp-2 gene, which codes for the abundant larval serum protein 2, were the subject of detailed study. None was rescued by the active Lsp-2 gene transformed on to chromosome II and we conclude that, as yet, we have no lethal mutations of Lsp-2.

Animals↗
PubMed1987

The molecular basis for metameric pattern in the Drosophila embryo.

The metameric organization of the Drosophila embryo is generated in the first 5 h after fertilization. An initially rather simple pattern provides the foundation for subsequent development and diversification of the segmented part of the body. Many of the genes that control the formation of this pattern have been identified and at least twenty have been cloned. By combining the techniques of genetics, molecular biology and experimental embryology, it is becoming possible to unravel the role played by each of these genes. The repeating segment pattern is defined by the persistent expression of engrailed and of other genes of the 'segment polarity' class. The establishment of this pattern is directed by a transient molecular prepattern that is generated in the blastoderm by the activity of the 'pair-rule' genes. Maternal determinants at the poles of the egg coordinate this prepattern and define the anteroposterior sequence of pattern elements. The primary effect of these determinants is not known, but genes required for their production have been identified and the product of one of these, bicoid is known to be localized at the anterior of the egg. One early consequence of their activity is to define domains along the A-P axis within which a series of 'cardinal' genes are transcribed. The activity of the cardinal genes is required both to coordinate the process of segmentation and to define the early domains of homeotic gene expression. Further interactions between the homeotic genes and other classes of segmentation genes refine the initial establishment of segment identities.

Animals↗
PubMed1985

Altered distributions of Ultrabithorax transcripts in extra sex combs mutant embryos of Drosophila.

The product of the extra sex combs (esc) gene is required early in embryogenesis to ensure the correct spatial expression of the bithorax and Antennapedia gene complexes during subsequent development. Here we describe the spatial and temporal patterns of transcription of the Ultrabithorax (Ubx) gene in mutant esc embryos. In wild-type embryos, Ubx transcripts are first detected in the blastoderm primorida of particular thoracic and abdominal segments, predominately in a band of cells constituting the progenitor cells of parasegment 6: after gastrulation, high levels of transcript accumulate in a sharply restricted region of the germ band comprising parasegments 6-12. In esc- embryos, the initial pattern of Ubx transcripts appears indistinguishable from that of wild-type embryos. However, following gastrulation and germ band extension, Ubx transcripts accumulate in most of the ectodermal and mesodermal derivatives of the body, including those of all 14 parasegments. Then, the abundance of the transcripts declines so that after germ band shortening (12 h after fertilization), only low levels are detected in each parasegment. These results show that the esc gene product is not involved in choosing where the Ubx gene is to be expressed, but rather, that it acts subsequently to ensure that the gene remains off in those primordia in which it is not initially activated. In addition, they suggest the possibility that other homeotic genes may regulate Ubx expression --in this case, the accumulating products of other indiscriminately expressed homeotic genes serving to down-regulate Ubx transcription throughout the body.

Animals↗