Sco, l(2)br28, l(2)br29, l(2)35Db, br29
transcription factor - zinc finger - DV polarity - a transcriptional repressor - acts to restrict neuroectoderm and neural fate in the invaginating mesoderm - mutants display a massive derepression of mesectoderm - controls proliferation of ovarian epithelial follicle stem cells
Gene model reviewed during 5.52
There is only one protein coding transcript and one polypeptide associated with this gene
390 (aa); 43 (kD predicted)
Click to get a list of regulatory features (enhancers, TFBS, etc.) and gene disruptions (point mutations, indels, etc.) within or overlapping Dmel\sna using the Feature Mapper tool.
Comment: reported as procephalic ectoderm primordium
Comment: reported as procephalic ectoderm primordium
Comment: reported as procephalic ectoderm primordium
In stage 12 embryos, sna is expressed in both the anterior and posterior lobes of the optic primordium.
Expression assayed at stages 9, 11, 13, and 17. Expression may be continuous between assayed stages in some tissues.
sna transcript expression is first detected during the cellular blastoderm stage, in presumptive mesodermal cells. Mesodermal expression fades during germband elongation, when sna expression begins to be detected in the ectoderm. The initial pair-rule pattern of sna expression gives way to a segmentally repeated pattern of cells interconnected by longitudinal rows of cells also expressing sna. Neuroblasts will delaminate at approximately the sites of these longitudinal rows of cells during the S1 phase of neuroblast segregation. At about 5.5 hours, sna expression is seen in both the nascent neuroblasts and in ectodermal cells. As neuroblast segregation nears completion at about 5.5 to 6 hours, sna expression is restricted to the neuroblast layer. By 6.5 to 7 hours, sna transcript is expressed in all neuroblasts and in PNS precursors. As in the CNS, sna transcript expression in the PNS begins in neurectodermal patches. Later, sna transcript is detected in sensory mother cells. At about 9 to 10 hours, sna is expressed in the postmitotic cells of the PNS and CNS. Starting at about 11 hours,and continuing into the first larval instar, sna is expressed in the precursors of the wing and haltere discs.
In wild type embryos at embryonic cycle 13, sna transcript is found at low levels ventrally in a region 12 to 14 nuclei-wide. At embryonic cycle 14, sna transcript is expressed at higher levels and in about an 18 cell-wide strip (the presumptive mesoderm), and the borders of expression continue to be fuzzy. By the onset of cellularization, the borders of sna transcript expression in the 18 ventral cells have sharpened, and end at the mesoderm-neurectoderm boundary. In a twi mutant background, level of sna transcript remains low, and is limited to the ventral-most 12-14 cells.
The early accumulation of sna transcript in wild-type embryos is consistent with the role of sna in mesoderm formation, but its later expression pattern suggests that sna might have additional functions. Prior to gastrulation, sna transcript is detected in the mesoderm and anterior midgut anlagen. Before germ band elongation at stages 7-9, sna transcript is present at the dorsal surface of the amnioproctodeal invagination and in the anterior midgut rudiment. Starting at late stage 8, and persisting through stage 11, sna transcript is also observed in some large neurectodermal cells, presumably neuroblast precursors and segregated neuroblasts. Later in embryogenesis, sna is expressed in cells which might be the precursors of the peripheral nervous system (stage 10), P cells (stages 11-14), dorsal mesothoracic disc (stage 13), dorsal metathoracic disc (stage 13), and Bolwig photoreceptor organs (stage 13).
Both twi and sna transcript are first detectable during nuclear cycle 12 as a diffuse band half the width of the presumptive mesoderm. Although the expression patterns of sna and twi transcript and protein are similar early in embryogenesis, there are some subtle differences. At mid-cellularization, the sna transcript and protein expression boundaries sharply delimit the presumptive mesoderm. At the same time, twi transcript and protein is expressed in a gradient that extends slightly past the sna expression zone into the presumptive ectoderm. The twi transcript and protein expression pattern gets sharper later, during gastrulation. twi protein is expressed in the mesoderm throughout germ band extension, whereas the sna protein product disappears from the mesoderm partway through germ band extension, and appears in neurectodermal cells which might be neuroblasts.
At stage 5 of embryogenesis, sna protein is expressed ventrally, in the presumptive mesoderm, while esg protein is expressed in the dorsal region. By stage 13, both sna and esg proteins are expressed in presumptive wing and haltere discs. At stage 15, sna and esg proteins are also expressed in the genital disc. The esg protein is detected in the posterior spiracle and in the presumptive leg discs at stage 15, while the sna protein is expressed in a far smaller number of cells in the presumptive leg discs.
While sna transcript is expressed at high levels in in the neurectoderm, sna protein is not detected in these cells. sna transcript and protein expression overlap in other tissues such as presumptive mesodermal cells during the blastoderm stage, and in postmitotic neurons.
sna transcript is first detected during the syncytial blastoderm stage, whereas sna protein expression is first detected during gastrulation. After this initial lag, the expression of sna protein and transcript overlap to a great extent, with some differences apparent after the start of germ band elongation at stage 7. In stage 6 of embryogenesis, sna protein is detected in the mesoderm and the anterior midgut primordium. At stage 7, it is found in the anterior and posterior transverse furrows, as well as the cephalic furrow. Between stages 9 and 11, sna protein is present in the neurectoderm. In late embryogenesis, weak staining is observed in presumptive wing and haltere discs.
Both twi and sna transcript are first detectable during nuclear cycle 12 as a diffuse band half the width of the presumptive mesoderm. Although the expression patterns of sna and twi transcript and protein are similar early in embryogenesis, there are some subtle differences. At mid-cellularization, the sna transcript and protein expression boundaries sharply delimit the presumptive mesoderm. At the same time, twi transcript and protein is expressed in a gradient that extends past the sna expression zone into the presumptive ectoderm. The twi transcript and protein expression pattern gets sharper later, during gastrulation. twi protein is expressed in the mesoderm throughout germ band extension, whereas the sna protein product disappears from the mesoderm partway through germ band extension, and appears in neurectodermal cells which might be neuroblasts.
GBrowse - Visual display of RNA-Seq signalsView Dmel\sna 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: sna CG3956
The "Sco" (Scutoid) mutant allele was previously listed as an allele of noc in FlyBase, as genetic analysis showed that a high dose of the wild-type noc gene suppresses the expressivity of the Sco phenotype, suggesting that Sco was an antimorphic allele of noc (FBrf0038047). However, FBrf0111871 shows that Sco is in fact an antimorphic allele of sna, and the mutant phenotype is caused by ectopic expression of sna in the eye-antennal and wing imaginal discs. The Sco allele is therefore now listed as an allele of sna in FlyBase. FBrf0111871 suggests that the reason that noc in trans affects the expressivity of Sco may be due to transvection effects, as they show that mutations in z, a mediator of transvection, also affect the Sco mutant phenotype.
dsRNA has been made from templates generated with primers directed against this gene. RNAi of sna causes dorsal overextension of primary dendrites in ddaD and ddaE neurons. For such neurons, the most distal branchpoint is located 25 microns or further from the distal tip of the primary dendrite. However, branching of these dendrites is almost completely blocked. RNAi also causes defects in muscle, defects in dendrite morphogenesis and reproducible defects in da dendrite development.
The normal location of the ventral furrow in embryos with uniformly expressed fog suggests the existence of a fog-independent pathway determining mesoderm-specific cell behaviours and invagination. Epistasis experiments indicate this pathway requires sna but not twi expression.
Expression of esg in the neuroectoderm is studied, the expression pattern prefigures that of the ASC genes. Dorsoventral pattern of esg expression in the blastoderm is determined by three independent repressive cues (dpp, sna and twi).
esg and sna function as intrinsic determinants of wing cell fate. esg and sna expression in the wing are maintained by their auto- and crossactivation, and control the same set of genes required for wing development.
The Kr and sna proteins function as short range repressors, which can mediate either quenching or direct repression of a transcription complex, depending on the location of repressor sites. Local quenching and dominant repression require close linkage of the repressor with either upstream activators or the transcription complex.
Deletion analysis of the sna promoter suggests that sequences directing expression in the CNS can be separated from those required for expression in the PNS.
sna is sufficient to induce the formation of an attenuated ventral furrow in the absence of twi+ gene activity. Expression of sna in the absence of twi uncouples ventral furrow formation and mesoderm differentiation, invaginating cells fail to express various mesoderm marker genes.
Mesodermal fate is determined where sna and twi but not hkb are expressed. Anteriorly, hkb together with sna determines endodermal fate, and hkb together with twi and sna are required for foregut development.
Promoter fusions using elements of the twi, rho, da and sna promoters indicate that low affinity dl-binding sites restrict target gene expression to the presumptive mesoderm, where there are peak levels of dl expression, while high affinity sites in other target genes permit expression in ventrolateral regions where dl levels are intermediate. Activation by low levels of dl in lateral regions depends on cooperative interaction between dl and other basic helix loop helix proteins. Promoters containing the Et (rho) or Eds (dl and sna) E boxes display opposite behaviour in da and twi mutants, suggesting they are regulated by different basic helix loop helix proteins.
In mutant embryos lacking the entire mesoderm or failing to differentiate the visceral mesoderm, the anterior and posterior midgut primordia form but do not migrate properly. The cells of these primordia fail to arrange into an epithelium.
sna mutants fail to differentiate ventrally derived mesoderm.
Expression patterns of various sna-Ecol\lacZ reporter gene constructs have revealed that 2.8kb of sna 5' flanking sequence contains most of the cis-regulatory elements responsible for both the early and late phases of normal sna pattern.
sna proposed to be a target of the dl morphogen. A sna repressor site has been found in the neural ectoderm expression region (NEE) of rho. Disruption of sna binding site causes derepression of rho expression in the ventral region therefore sna is responsible for establishing the mesoderm/neurectoderm boundary before gastrulation.
The zygotically acting DV genes repress ac expression within specific DV domains.
Sequence alignments of orthologous fragments of hb, Kr and sna from a variety of arthropods and other phyla show that amino acid differences are not normally correlated with evolutionary distance between respective species. Amino acids directly involved in DNA binding are the most conserved, and binding specificity of a hb finger from different species is not changed.
The expression of sna RNA and protein throughout embryogenesis has been studied.
The effect of the terminal system on the expression of 2 zygotic genes involved in dorsoventral patterning, sna and dpp, is mediated by a reduction in dl activity by the terminal system. Due to this interaction the poles adopt a more dorsalised fate than their counterparts in the middle of the embryo.
sna prevents expression in the mesoderm of genes that are destined to be active only in more lateral or dorsal regions.
Mutations in zygotic ventral class gene sna interact with RpII140wimp.
In sna mutant embryos the ventral furrow fails to form at gastrulation resulting in an absence of all mesodermal derivatives in the mature embryo.
Polar expression of sna requires genes of the terminal group.
Zygotically active locus involved in the terminal developmental program in the embryo.
17 additional alleles are discussed but are not named.