Hw, T5, AS-C T5, EG:125H10.3 , achaete-scute
Gene model reviewed during 5.39
Supported by strand-specific RNA-Seq data.
Gene model reviewed during 5.51
There is only one protein coding transcript and one polypeptide associated with this gene
23 (kD predicted)
Efficient DNA binding requires dimerization with another bHLH protein.
Click to get a list of regulatory features (enhancers, TFBS, etc.) and gene disruptions (point mutations, indels, etc.) within or overlapping Dmel\ac using the Feature Mapper tool.
ac is expressed in four clusters of neuroectodermal cells per hemi-segment of a wild-type stage 8 embryo, including two in the ventral column, and two in the lateral column.
The first wave of ac expression occurs at embryonic stage 7 in 12-16 clusters of cells arranged on either side of the ventral midline. During stage 8, the clusters appear to split and expression is observed in a second row of clusters so that by the end of stage 8 there are 4 ac-expressing clusters per hemisegment, each containing 4-6 ectodermal cells. Then one cell begins to accumulate higher ac levels and delaminates from the ectoderm. The delaminated neuroblast continues to express high levels of ac RNA while the remaining ectodermal cells no longer express ac. Only a subset of the embryonic neuroblasts derive from ac RNA-expressing cells. A second round of ac transcript expression occurs in the ventral epidermis at stage 11 coincident with the third round of neuroblast segregation. ac transcripts are also expressed in the lateral ectoderm from the beginning of stage 10 until mid stage 11. ac-expressing cells from the first two clusters of ac expression give rise to SMCs that are precursors to the multiply innervated sense organs. Other ac-expressing SMCs give rise to a mapped set of sensory organs.
ac transcripts first accumulate in late stage 8 embryos in a segmentally repeated pattern of two medial and two lateral clusters of 5-7 ectodermal cells per hemisegment. One cell per cluster, the future neuroblast, comes to express ac most intensely and delaminates toward the interior of the embryo. The remaining cells in the ectodermal cluster lose ac expression. Expression of ac transcripts in the neuroblast ceases after it has delaminated from the ectoderm and before it begins dividing. In mutants of N, Dl, bib, neur, and E(spl), most to all cells of the cluster retain high level ac expression.
ac transcripts are present in proneural clusters prior to the emergence of SMCs. Expression continues as the SMC develops and is higher in the SMC than the surrounding cells.
ac trancripts are expressed in clusters of cells in the wing imaginal disc. The locations of the clusters coincides well with the pattern of sensory organ precursors.
ac transcripts are observed in the early gastrula in a striped pattern (one stripe per metamere) in the presumptive neurectoderm. Between stages 8 and 9, the pattern changes to two stripes per metamere. Later ac is expressed in the segregating neuroblasts but not in the remaining ectodermal cells. ac expression declines in neuroblasts at stage 9 as they start dividing. This pattern repeats itself as additional cells in the ectodermal layer express ac. Expression continues in cells that become neuroblasts and shuts off in cells that remain ectodermal. ac transcripts are also observed in cephalic neuroblasts and in the posterior midgut. In subsequent stages, ac transcripts disappear from the metameric germ band and are seen only in the primordia for the stomatogastric nervous system and the optic lobes.
ac and sc transcripts are detected in a dynamic pattern from blastoderm (sc) or gastrula (ac) through stage 11 embryos. They are present in clusters of cells on the ectoderm and internally near the mesoderm. They are expressed in most neurogenic regions. Their expression patterns are very similar except in stage 9 where sc is barely detectable and ac is expressed in four longitudinal rows of clusters.
acHw-1 transcripts have a bimodal developmental profile with peaks of expression in 0-12hr embryos and 0-1 day pupae. acHw-1 transcripts in acHw-1 larvae and pupae are 5-20 times more abundant than ac transcripts in wild type larvae and pupae. A 200-fold reduction in acHw-1 transcript levels is observed in acHw-1+R1 revertants relative to the parent acHw-1. In FBal0000169:ac<up>Hw-1+R3< /up> revertants, the level of FBal0000167:ac<up>Hw-1< /up> transcripts is reduced less drastically and in FBal0000170:ac<up>Hw-1+R5< /up> revertants, it is reduced only 1.5 to 2-fold. FBal0000167:ac<up>Hw-1< /up> transcript levels are reduced 2- to 3-fold in the presence of FBgn0003567:su (Hw)@ in third instar larvae and pupae and are unchanged at earlier stages.
ac protein is present in MP1 and transiently in MP5, MP6, and MNB at embryonic stages 10-11. It remains in the MP1 neurons after division throughout embryogenesis. It is absent in all other midline neurons and in midline glia.
ac is expressed in the dorsal-proximal region of leg discs and is limited to the region of overlap between ss and al expression. Expression is observed from third instar at least until early pupal stages.
ac protein is expressed in the sensory mother cells along the dorsal/ventral compartment boundary of the wing disc.
Expression in procephalic neuroblasts stage 9-11: deuterocerebrum - d2, d3, d8, v6; protocerebrum - ad1, ad4, cd3, cd6, cd8, cd9, cd15, cd16, cd19, cd21, cv3, cv7, cv9, pd11, pv2
In stages 8-11 ac and l(1)sc proteins are expressed in a dynamic pattern in the procephalic neurectoderm in a largely complementary pattern. By stage 8 l(1)sc protein is detected in a large central domain and as development proceeds the area of protein expression increases. The first proto and deuterocerebral neuroblasts develop from this area. About 60% of all neuroblasts formed until stage 11 express l(1)sc. In stage 8 ac expression is detected in a small dorsal ocular and antennal group of cells. In stage 9 ac expression expands to several large domains in the neuroectoderm.
Expression of ac and sc in ectopic sensilla of h and acHw* mutants was followed with antibody staining. The pattern of expression of ac and sc prefigures the pattern of both ectopic and normal sensilla.
The ac protein is expressed in a specified subset of neuroblasts in embryonic stages 8-11. (see also FBrf 55911)
ac protein first accumulates in late stage 8 embryos in a segmentally repeated pattern of two medial and two lateral clusters of 5-7 ectodermal cells per hemisegment. One cell per cluster, the future neuroblast, comes to express ac most intensely and delaminates toward the interior of the embryo. The remaining cells in the ectodermal cluster lose ac protein expression. Expression of ac protein in the neuroblast ceases after it has delaminated from the ectoderm and before it begins dividing. In mutants of N, Dl, bib, neur, and E(spl), most to all cells of the cluster retain ac protein expression at high levels.
ac protein is localized within nuclei of proneural clusters. Clusters grow in number and intensity of staining until the sensory organ mother cell (SMC) becomes discernable due to its more intensely stained nucleus. The ac protein disappears shortly before the SMC undergoes its first differential division.
ac protein expression occurs in clusters of cells from which SMCs will arise. It is transiently expressed in the SMCs, often at greater levels than the surrounding cells of the proneural cluster, but not in their progeny. In sc mutants, ac protein expression is missing in the notal cells that give rise to sc-dependent machrochaetes. In emc mutants, ectopic ac protein expression occurs in single cells of the notum that will give rise to ectopic sensory organs. In h mutants ectopic ac protein expression occurs in regions of the imaginal wing blade that will give rise to ectopic sensory organs. Ectopic h expression represses ac expression. An acHw-49c mutation causes overexpression of ac protein.
GBrowse - Visual display of RNA-Seq signalsView Dmel\ac in GBrowse 2
Please Note This section lists cDNAs and ESTs that fall within the genomic extent of the gene model, which may include cDNAs and ESTs of genes within introns, or of overlapping genes. Please see GBrowse for alignment of the cDNAs and ESTs to the gene model.
For each fully sequenced cDNA the DGRC maintains various forms of the cDNA (e.g tagged or untagged) in several different host vectors for subsequent cloning and expression in Drosophila and Drosophila cell lines.
Source for identity of: ac CG3796
The promoter region of ac contains three E-boxes and an S-box. Although each E-box contributes to the wild-type level of transcription, E1 is more important than E2 and E3. When the S-box is mutated, even the presence of E1 or E2 sites alone is enough to mediate sens-proneural synergism.
pnr directly activates the proneural ac and sc genes by binding to the enhancers responsible for their expression in the dorsocentral proneural cluster. wg has only a permissive role on dorsocentral ac-sc expression.
Candidate gene for quantitative trait (QTL) locus determining bristle number.
In a sample of 79 genes with multiple introns, 33 showed significant heterogeneity in G+C content among introns of the same gene and significant positive correspondence between the intron and the third codon position G+C content within genes. These results are consistent with selection adding against preferred codons at the start of genes.
E(spl) proteins normally mediate lateral inhibition by directly repressing proneural gene expression.
The bHLH domains of the gene products encoded by the E(spl)-C and the achaete-scute complex differ in their ability to form homo- and/or heterodimers. The interactions established through the bHLH link the products of the two complexes in a single interaction network which may function to ensure that a given cell retains the capacity to choose between epidermoblast and neuroblast fates until the cell becomes definitively determined.
Mutations show weak interactions with high and low selection lines, abdominal and sternopleural bristle numbers are affected. Results suggest ac is in the same genetic pathway as bristle number quantitative trait loci (QTL).
All proneural proteins are similarly able to promote the segregation of a neural precursor at the MP2 neuroblast position but show distinct capacities in its specification.
The presence of ac and sc contribute to the neural precursor identity of MP2. The function of l(1)sc is not interchangable with that of ac or sc within the MP2, specification of MP2 is similar in embryos lacking ac/sc compared with those lacking ac/sc plus ectopic l(1)sc expression.
The expression pattern of proneural genes of the achaete-scute complex and neurogenic genes of the E(spl)-C are examined in the procephlon and a map of the cells is constructed.
cas, eve, unpg and ac are expressed in specific neuroblast sublineages. Expression studies using pbl and stg mutants suggest that neuroblasts have an intrinsic gene regulatory hierarchy controlling unpg and ac expression but that cell cycle- or cytokinesis-dependent mechanisms are required for cas and eve CNS expression.
A 900bp ac promoter fragment can be activated by binding of activators to three E-boxes and repressed via binding of h. The repression domain of h has mapped to a region containing the carboxyl terminus of the protein, this region is both necessary and sufficient for the repression of the ac promoter.
Loss of function mutations in the achaete-scute complex lead to a significant reduction in sensory bristles and glial cells. Neurogenesis and gliogenesis share the same genetic pathway, though the mechanism of action of the the achaete-scute complex is different in the two processes. Gliogenesis may be induced by the presence of sensory organ cells, either the precursor or its progeny.
The highly complex pattern of proneural clusters is constructed piecemeal by the action of site-specific enhancer like elements on ac and sc. These elements are distributed along most of the achaete-scute complex. The cross-activation between ac and sc does not occur detectably between the endogenous ac and sc genes in most proneural clusters. Coexpression is accomplished by activation of both ac and sc by the same set of position-specific enhancers.
Examination of the ac expression and the sensory mother cell arrangement in N mutations demonstrates that processes of cellular and molecular interactions mediated by N gene products are responsible for the establishment of stripes of ac expression.
Ectopic expression does not affect the viability of either sex, but it does rescue the female lethality caused by ectopic expression of h.
ac-sc complex genes are expressed in neuronal precursor cells, so expressed ventrally in insects and vertebrate homologs are expressed dorsally. This situation is thought to have evolved due to an inversion of the dorsoventral axis. The inversion occurred during early chordate evolution, the chordates turned upside down and henceforth were carrying the nerve cord on their dorsal side.
Proneural gene products (ac, da and l(1)sc) activate transcription of Dl in the neuroectoderm by binding to specific sites within its promoter. This transcriptional activation enhances lateral inhibition and helps ensure that cells in the vicinity of prospective neuroblasts will themselves become epidermoblasts.
DNaseI footprinting analysis of bacterially expressed E(spl) and HLHm5 demonstrates the gene products can bind as homo- and heterodimers to a sequence in the promoters of the E(spl) and ac genes, called the N-box, which differs slightly from the consensus binding site for other bHLH proteins.
h binds to DNA, preferably at a noncanonical site, and has a novel DNA binding activity. Mutation of a single h binding site in ac blocks h mediated repression of ac transcription in culture cells and creates ectopic sensory hair organs in vivo. Results indicate that h represses sensory organ formation by directly repressing transcription of the ac gene.
Electrophoretic mobility shift assays demonstrate that Brd, sca, m4, HLHm7 and E(spl) are directly activated in proneural clusters of the late third-instar wing imaginal disc by protein complexes that include the ac and sc bHLH proteins.
vnd controls neuroblast formation, in part, through its regulation of the proneural genes of the ac-sc complex. vnd controls proneural gene expression at two distinct steps during neuroblast formation through separable regulatory regions.
At the DNA sequence level D.melanogaster populations from Zimbabwe are more than twice as variable as populations from U.S.A. Most variants are not shared between the two geographic regions and areas of low recombination rates have mutations that are nearly fixed.
The ato gene was identified in a PCR screen for genes sharing features with the basic helix loop helix domains of the achaete-scute genes.
Ecol\lacZ reporter gene constructs demonstrate that regulation of ac requires E-boxes present in its promoter. emc down regulates the ac promoter. Modified emc can interfere with the binding of proneural proteins to an ac E-box.
Regulation of the h and ac expression patterns partitions the leg epidermis into striped zones that correspond to the pattern of longitudinal rows of leg bristles.
Ectopic expression shows that ac displays weak but significant feminizing activity.
Human achaete and scute homolog, hASH1 has been identified and is highly expressed in neuroendocrine tumors.
Mutants associated with lesions in the zinc finger domain of pnr show overexpression of ac and sc and the development of extra neural precursors. Mutations in the putative amphipathic helices of pnr act as hyperactive repressor molecules causing a loss of ac and sc expression and a loss of neural precursors.
The specific combination of achaete-scute complex genes expressed at one site does not play a role in defining the fate of the progenitor cell that is formed at that site. Individual sense organs depend mostly or exclusively on one of the achaete-scute complex genes because the cis-regulatory sites active at the corresponding location act mostly or exclusively on that particular gene.
Enhancer trap lines were used to follow the development of ectopic sensillar precursors in wings of h and Hairy-wing ac mutants: ectopic sensilla appear correlated with ectopic achaete and scute expression. Results suggest that both h and ac act to induce the formation of temporally and spatially distinct phase of sensillar development.
Expression analysed in CNS study of neuroblasts and ganglion mother cells.
A 2.2 kb region including the ac, sc and y genes in D.simulans has been sequenced and interspecific and intraspecific divergence calculated with D.melanogaster. The level of heterozygosity in the y-ac-sc region exceeds that in the Adh 5' flanking region: the silent divergence is not reduced compared to other regions so the reduction in levels of variation can only be explained by a hitchhiking effect of linked selected substitutions.
In situ hybridization and immunohistochemical inspection of embryos demonstrated that the ac RNA and protein patterns are identical. ac protein distribution in embryos mutant for N, Dl, E(spl), bib and neu show ac expression is not restricted to a single cell of an ectodermal cell cluster, as for wild type, instead most cells of the cluster retain ac expression at a high level, enlarge, delaminate and become neuroblasts. Neurogenic genes silence proneural gene expression within the non segregating cells of the ectodermal cell cluster, allowing epidermal development.
In the embryo, ac and sc are expressed coincidentally, at reproducible anterior-posterior and dorso-ventral coordinates, in clusters from which neuroblasts will arise. The AP and DV position is regulated through a common regulatory element between ac and sc that is under the control of pair rule, segment polarity and DV patterning genes.
Sensory mother cells arise from clusters of mitotically quiescent cells identified by BrdU immunolabelling to monitor mitotic activity: the cell that becomes the sensory mother cell was arrested at the G2 stage of the cell cycle. Emergence of mitotically quiescent cells follows precise temporal and spatial pattern and is not affected by ac or sc mutations.
Direct, positive transcriptional autoregulation by the ac protein and cross-regulation by sc are essential for high level expression of the ac promoter in the proneural cluster. Auto-activation of ac is important for the bristle-promoting function of the ac gene. These auto- and cross-regulatory activities are antagonized in a dose-dependent manner by the emc gene product. In cotransfection studies the highest levels of ac expression are achieved when a combination of ac and da or sc expression vectors are present in the cotransfection mixture. Proper expression of ac-lacZ in flies depends on da/ac-sc DNA binding sites.
In vitro DNA binding assays using gel retardation to an ac promoter region and hb zygotic promoter region target sequence demonstrates that da protein elicits a weak homodimeric binding and da/ac or da/sc heterodimers bind tightly.
Genetic mosaic analysis of cells with different doses of ac demonstrates that the levels of the gene product determine SMC formation and maintenance.
Ecol\lacZ reporter gene constructs have been used to examine the ac expression pattern. Results indicate that expression of ac stimulates expression of sc, and visa versa, therefore removal of one gene leads to the absence of both proneural gene products and sensory organs in the sites specificed by it cis-regulatory sequences.
DNA sequence analysis reveals four E box binding sites, for the binding of hetero-oligomeric complexes composed of da or the achaete-scute complex proteins, in the first 877 bp of the ac upstream region. Electrophoretic mobility shift assays demonstrate that the emc protein can specifically antagonise DNA binding of the da/the achaete-scute complexes in vitro in a dose-dependent manner, h and E(spl) proteins fail to exhibit this inhibitory effect.
Loss-of-function mutants cause loss of specific clusters of bristles, while gain-of-function mutants cause the appearance of ectopic bristles.
Analysis of flies deficient for the sc and/or ac genes shows that the complete pattern of campaniform sensilla on the wing results from the superimposition of two independent subpatterns, one of which depends on sc, the other on ac.
The ac and sc gene products are required for the spatial positioning of sensory organs in late third instar larval wing discs. ac and sc are expressed in the same regions where part of the sensory organ precursors are differentiating and the expansion of the area of ac and sc expression causes ectopic expression of sensory organs. h and emc do not modify the ac/sc patterns of expression in the wing disc.
Sequence analysis reveals that ac, sc and l(1)sc transcription units share highly conserved acidic and basic domains in their protein coding regions. The basic domain of the ac, sc and l(1)sc proteins show similarity to the vertebrate myc and MyoD proteins.
Transcripts of ac, sc and l(1)sc accumulate at the blastoderm stage in periodic patterns within the neuroectoderm. Subsequent expression is in partially overlapping patterns that correlate with the segregation of the neuroblasts.
The achaete-scute complex defines the basic topology of the sense organ pattern, rather than the type or precise location of the elements. The achaete-scute complex is an essential component of es and nd neuron development. ac is sufficient for the development of Class A neurons. The ac function can to some extent be substituted by sc and possibly l(1)sc.
The patterns of expression of ac, sc and l(1)sc are complex and evolve rapidly, affecting most if not all the known neurogenic regions. Gene expression precedes and is concomitant with the histological appearance of precursors of neural cells. The achaete-scute complex plays a role in determination and early differentiation of embryonic neural cells.
An increase of ac doses in h- homozygous flies produces an increase in microchaetae density on the notum and wing. Above a maximum dose more doses of ac cause a reduction in microchaetae density in the notum but increase on the wing.
A member of the achaete-scute complex (ASC) ac specifies the formation of the anterior and posterior dorsocentral, the posterior supra-alar (as does sc), the anterior vertical bristle and in addition the acrostichal rows of microchaetae on the notum. Absence of bristles accompanied by absence of associated socket and underlying centrally projecting neuron (Stern, 1938). In addition mutant alleles of ac tend to remove the interocellar hairs and the hairs on the surface of the eye and a restricted subset of the campaniform sensilla on the wing blade (Leyns, Dambly-Chaudiere and Ghysen, 1989). Trichomes are not affected. ac deficiencies, e.g., In(1)y3PLsc8R, survive as fully mobile and fertile adults (Garcia-Bellido, 1979). A series of terminal deficiencies approaching the ac coding sequence from the left a few hundred base pairs at a time, when tested in heterozygotes with In(1)y3PLsc8R or Df(1)sc19, cause, with few exceptions, progressive loss of chaetae as the amount of deleted material increases; response of anterior verticals erratic. First effects of deficiencies noted with chromosomes broken 10 kb upstream of the transcription start site. Despite loss of most of the DNA upstream from the transcribed region, the phenotypes associated with these deletions still suppressed by emc and h (Ruiz-Gomez and Modolell, 1987). Deficiencies for ac act as suppressors of h (Sturtevant, 1970), whereas extra doses of ac+ enhance expression of h (del Prado and Garcia-Bellido, 1984). Longitudinal stripes of expression on either side of the midline during gastrulation become internalized and segmented into four longitudinal rows of clusters of expressing cells at half-segment intervals. ac RNA undetectable in germ band at time of germ-band shortening. Several regions of high expression seen in cephalic region. Also expressed in posterior midgut rudiment (Romani, Campuzano and Modolell, 1987; Cabrera, Martinez-Arias and Bate, 1987). In third instar larvae, expression in wing imaginal discs restricted to regions where precursors of cuticular organs specified by ac are known to reside (Romani, Campuzano, Macagno and Modolell, 1989). Alleles of the Hw series are gain of function alleles of the achaete-scute complex, which lead to the development of supernumerary bristles and hairs in all segments of the fly: in the prefrons, postfrons, postgena, and occipital regions of the head; in the preepisternum, episternum, anepisternum, scutum, scutellum, postnotum, wingblade, legs, humerus and halteres of the thorax; and in the tergites, pleura and sternites of the abdomen. Phenotype suppressed by three doses of h+ (Botas, del Prado and Garcia-Bellido, 1982) and enhanced by h, emc and pyd (Neel, 1941; del Prado and Garcia-Bellido, 1984). Numbers of super numerary bristles reduced in da+ hemizygotes (Dambly-Chaudiere, Ghysen, Jan and Jan, 1988).