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Biomedical subjects

S B Carroll

Publications and source records attributed to S B Carroll.

At least 55 records · Page 3Linked to original sources
PubMed1994

Pattern formation and eyespot determination in butterfly wings.

Butterfly wings display pattern elements of many types and colors. To identify the molecular processes underlying the generation of these patterns, several butterfly cognates of Drosophila appendage patterning genes have been cloned and their expression patterns have been analyzed. Butterfly wing patterns are organized by two spatial coordinate systems. One system specifies positional information with respect to the entire wing field and is conserved between fruit flies and butterflies. A second system, superimposed on the general system and involving several of the same genes, operates within each wing subdivision to elaborate discrete pattern elements. Eyespots, which form from discrete developmental organizers, are marked by Distal-less gene expression. These circular pattern elements appear to be generated by a process similar to, and perhaps evolved from, proximodistal pattern formation in insect appendages.

Amino Acid Sequence↗
PubMed1994

Organization of wing formation and induction of a wing-patterning gene at the dorsal/ventral compartment boundary.

The appendages of arthropods and vertebrates possess a third, proximodistal patterning axis that is established after the primary anteroposterior and dorsoventral body axes by mechanisms that are largely unknown. The vestigial gene is required for formation of the entire Drosophila wing, and the dorsal/ventral boundary is shown to organize wing formation and vestigial gene expression. Interactions between dorsal and ventral cells in the growing imaginal disc induce vestigial gene expression through a discrete, extraordinarily conserved imaginal disc-specific enhancer. The link between dorsal/ventral compartmentalization and wing formation distinguishes the development of this sheet-like appendage from that of legs and antennae.

Animals↗
PubMed1994

The achaete-scute complex: generation of cellular pattern and fate within the Drosophila nervous system.

In developing embryos, cells receive and interpret positional information as they become organized into discrete patterns and structures. One excellent model for understanding the genetic regulatory mechanisms that pattern cellular fields is the regulation and function of the achaete-scute complex (AS-C) in the developing nervous system of the fruit fly, Drosophila melanogaster. Three structurally homologous proneural genes--achaete (ac), scute (sc), and lethal of scute (l'sc)--are required for neural stem cell formation. In Drosophila, the AS-C genes are initially expressed in patterns of cell clusters at reproducible anteroposterior (AP) and dorsoventral (DV) coordinates that foreshadow where neural precursors arise. In the embryonic central nervous system (CNS), the gene products of AP and DV axis-patterning genes act combinatorially via a large array of cis-regulatory regions scattered throughout the AS-C to generate a segmentally repeated pattern of proneural clusters. Within each cluster (an equivalence group), one cell then retains proneural gene expression and is singled out as the neural stem cell (neuroblast). The neuroblast inhibits the surrounding cells from adopting neural fates (lateral inhibition) through a signaling pathway that is mediated via the action of the proneural and neurogenic genes. The proneural genes therefore represent a nodal point in the patterning of the nervous system. They receive global positional information, transduce it to discrete sets of cells, and trigger local cell interactions that mediate cell fate decisions.

Animals↗
PubMed1994

Positioning adjacent pair-rule stripes in the posterior Drosophila embryo.

We present a genetic and molecular analysis of two hairy (h) pair-rule stripes in order to determine how gradients of gap proteins position adjacent stripes of gene expression in the posterior of Drosophila embryos. We have delimited regulatory sequences critical for the expression of h stripes 5 and 6 to 302 bp and 526 bp fragments, respectively, and assayed the expression of stripe-specific reporter constructs in several gap mutant backgrounds. We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border. Interestingly, Krüppel (Kr) limits the anterior expression limits of both stripes and is the only gap gene to do so, indicating that stripes 5 and 6 may be coordinately positioned by the Kr repressor. In contrast to these very similar cases of spatial repression, stripes 5 and 6 appear to be activated by different mechanisms. Stripe 6 is critically dependent upon knirps (kni) for activation, while stripe 5 likely requires a combination of activating proteins (gap and non-gap). To begin a mechanistic understanding of stripe formation, we locate binding sites for the Kr protein in both stripe enhancers. The stripe 6 enhancer contains higher affinity Kr-binding sites than the stripe 5 enhancer, which may allow for the two stripes to be repressed at different Kr protein concentration thresholds. We also demonstrate that the kni activator binds to the stripe 6 enhancer and present evidence for a competitive mechanism of Kr repression of stripe 6.

Animals↗
PubMed1994

The ventral nervous system defective gene controls proneural gene expression at two distinct steps during neuroblast formation in Drosophila.

Within the Drosophila embryo, the formation of many neuroblasts depends on the functions of the proneural genes of the achaete-scute complex (AS-C): achaete (ac), scute (sc) and lethal of scute (l'sc), and the gene ventral nervous system defective (vnd). Here, we show that vnd controls neuroblast formation, in part, through its regulation of the proneural genes of the AS-C. vnd is absolutely required to activate ac, sc and l'sc gene expression in proneural clusters in specific domains along the medial column of the earliest arising neuroblasts. Using ac-lacZ reporter constructs, we determined that vnd controls proneural gene expression at two distinct steps during neuroblast formation through separable regulatory regions. First, vnd is required to activate proneural cluster formation within the medial column of every other neuroblast row through regulatory elements located 3' to ac; second, through a 5' regulatory region, vnd functions to increase or maintain proneural gene expression in the cell within the proneural cluster that normally becomes the neuroblast. By following neuroblast segregation in vnd mutant embryos, we show that the neuroectoderm forms normally and that the defects in neuroblast formation are specific to particular proneural clusters.

Animals↗
PubMed1993

Pattern formation in a secondary field: a hierarchy of regulatory genes subdivides the developing Drosophila wing disc into discrete subregions.

The legs and wings of insects and vertebrates develop from secondary embryonic fields that arise after the primary body axes have been established. In order to understand how the insect imaginal wing field is patterned, we have examined in detail the temporal and spatial expression patterns of, and epistatic relationships between, four key regulatory genes that are specifically required for wing formation in Drosophila. The wingless protein, in a role surprisingly distinct from its embryonic segment polarity function, appears to be the earliest-acting member of the hierarchy and crucial for distinguishing the notum/wing subfields, and for the compartmentalization of the dorsal and ventral wing surfaces. The wingless product is required to restrict the expression of the apterous gene to dorsal cells and to promote the expression of the vestigial and scalloped genes that demarcate the wing primordia and act in concert to promote morphogenesis.

Animals↗
PubMed1993

Conservation of regulatory elements controlling hairy pair-rule stripe formation.

The hairy (h) gene is one of two pair-rule loci whose striped expression is directly regulated by combinations of gap proteins acting through discrete upstream regulatory fragments, which span several kilobases. We have undertaken a comparative study of the molecular biology of h pair-rule expression in order to identify conserved elements in this complex regulatory system, which should provide important clues concerning the mechanism of stripe formation. A molecular comparison of the h locus in Drosophila virilis and Drosophila melanogaster reveals a conserved overall arrangement of the upstream regulatory elements that control individual pair-rule stripes. We demonstrate that upstream fragments from D. virilis will direct the proper expression of stripes in D. melanogaster, indicating that these are true functional homologs of the stripe-producing D. melanogaster regulatory elements, and that the network of trans-acting proteins that act upon these regulatory elements is highly conserved. We also demonstrate that the spatial relationships between specific h stripes and selected gap proteins are highly conserved. We find several tracts of extensive nucleotide sequence conservation within homologous stripe-specific regulatory fragments, which have facilitated the identification of functional subelements within the D. melanogaster regulatory fragment for h stripe 5. Some of the conserved nucleotide tracts within this regulatory fragment contain consensus binding sites for potential trans-regulatory (gap and other) proteins, while many appear devoid of known binding sites. This comparative approach, coupled with the analysis of reporter gene expression in gap mutant embryos suggests that the Kr and gt proteins establish the anterior and posterior borders of h stripe 5, respectively, through spatial repression. Other, as yet unidentified, proteins are certain to play a role in stripe activation, presumably acting through other conserved sequence tracts.

Amino Acid Sequence↗
PubMed1993

The spatial organization of epidermal structures: hairy establishes the geometrical pattern of Drosophila leg bristles by delimiting the domains of achaete expression.

The spatial organization of Drosophila melanogaster epidermal structures in embryos and adults constitutes a classic model system for understanding how the two dimensional arrangement of particular cell types is generated. For example, the legs of the Drosophila melanogaster adult are covered with bristles, which in most segments are arranged in longitudinal rows. Here we elucidate the key roles of two regulatory genes, hairy and achaete, in setting up this periodic bristle pattern. We show that achaete is expressed during pupal leg development in a dynamic pattern which changes, by approximately 6 hours after puparium formation, into narrow longitudinal stripes of 3-4 cells in width, each of which represents a field of cells (proneural field) from which bristle precursor cells are selected. This pattern of gene expression foreshadows the adult bristle pattern and is established in part through the function of the hairy gene, which also functions in patterning other adult sense organs. In pupal legs, hairy is expressed in four longitudinal stripes, located between every other pair of achaete stripes. We show that in the absence of hairy function achaete expression expands into the interstripe regions that normally express hairy, fusing the two achaete stripes and resulting in extra-wide stripes of achaete expression. This misexpression of achaete, in turn, alters the fields of potential bristle precursor cells which leads to the misalignment of bristle rows in the adult. This function of hairy in patterning achaete expression is distinct from that in the wing in which hairy suppresses late expression of achaete but has no effect on the initial patterning of achaete expression. Thus, the leg bristle pattern is apparently regulated at two levels: a global regulation of the hairy and achaete expression patterns which partitions the leg epidermis into striped zones (this study) and a local regulation (inferred from other studies on the selection of neural precursor cells) that involves refinement steps which may control the alignment and spacing of bristle cells within these zones.

Animals↗
PubMed1993

Three-color immunofluorescence imaging of Drosophila embryos by laser scanning confocal microscopy.

We present a simple means for triple-labeling biological specimens by immunofluorescence using a laser scanning confocal microscope for imaging with a krypton/argon laser as a light source. Three separate images of fluorescein-, lissamine rhodamine- and cyanine-5-labeled antibodies are collected and subsequently merged to form the triple-labeled image, which is displayed at full-image resolution (24 bit) on a second image processing system. The technique is illustrated using immunofluorescence localization of three segmentation proteins in Drosophila embryos.

Animals↗
PubMed1992

Comparison of the purity and efficacy of affinity purified avian antivenoms with commercial equine crotalid antivenoms.

Antivenoms were raised in laying hens by repeated immunizations with detoxified crotalid snake venoms and purified from egg yolks by affinity chromatography. While the affinity purified avian antivenoms were essentially pure IgG, commercial equine (Wyeth) and W.H.O. international reference antivenoms (Trimeresurus flavoviridis) contained several non-immunoglobulin contaminants. In standard mouse protection assays, the purified avian Crotalus atrox and T. flavoviridis antivenoms were 6.3 and 2.0 times as potent, respectively, as these equine antivenoms in neutralizing venom lethality. The purity, efficacy, and ease of manufacture of avian antivenoms, and their inability to fix mammalian complement, make them an attractive alternative to equine and other mammalian antivenoms.

Animals↗
PubMed1992

Gene regulation in two dimensions: the proneural achaete and scute genes are controlled by combinations of axis-patterning genes through a common intergenic control region.

The mechanisms that generate precise patterns of discrete cell types within developing fields are not well understood. One model for analyzing how cells interpret positional information in two dimensions is the regulation of proneural cluster formation within insect segments. Two adjacent proneural regulatory genes, achaete and scute, are expressed coincidently in cell clusters at reproducible anteroposterior (AP) and dorsoventral (DV) coordinates within the Drosophila embryo from which single neuroblasts later arise. Here, we show that the AP and DV position of these clusters is regulated through a common cis-acting region between the genes under the initial control of the products of the pair-rule and DV polarity genes and is later maintained by selected segment polarity genes. The combination of proneural gene activation/repression in AP stripes and repression within specific DV domains positions each cluster of achaete/scute expressing cells within segments; interactions between these cells then determine individual cell fates.

Animals↗
PubMed1992

Regulation of proneural gene expression and cell fate during neuroblast segregation in the Drosophila embryo.

The Drosophila embryonic central nervous system develops from sets of progenitor neuroblasts which segregate from the neuroectoderm during early embryogenesis. Cells within this region can follow either the neural or epidermal developmental pathway, a decision guided by two opposing classes of genes. The proneural genes, including the members of the achaete-scute complex (AS-C), promote neurogenesis, while the neurogenic genes prevent neurogenesis and facilitate epidermal development. To understand the role that proneural gene expression and regulation play in the choice between neurogenesis and epidermogenesis, we examined the temporal and spatial expression pattern of the achaete (ac) regulatory protein in normal and neurogenic mutant embryos. The ac protein is first expressed in a repeating pattern of four ectodermal cell clusters per hemisegment. Even though 5-7 cells initially express ac in each cluster, only one, the neuroblast, continues to express ac. The repression of ac in the remaining cells of the cluster requires zygotic neurogenic gene function. In embryos lacking any one of five genes, the restriction of ac expression to single cells does not occur; instead, all cells of each cluster continue to express ac, enlarge, delaminate and become neuroblasts. It appears that one key function of the neurogenic genes is to silence proneural gene expression within the nonsegregating cells of the initial ectodermal clusters, thereby permitting epidermal development.

Animals↗
PubMed1991

Control of Drosophila wing and haltere development by the nuclear vestigial gene product.

The Dipteran flight appendages, the wings and halteres, develop from larval imaginal discs that also produce other sections of the second and third thoracic adult body segments. Loss of vestigial (vg) function in Drosophila selectively eliminates wing and haltere formation. Here, we show that vg expression is spatially restricted to the presumptive wing and haltere regions of these imaginal discs. An intronic regulatory element mediates this restriction and may elaborate upon cues that activate vg expression in the embryonic disc primordia. The nuclear vg protein lacks any recognized nucleic acid-binding motif but is comprised of two putative functional domains, one of which bears similarity to part of the Deformed homeotic protein and may mediate protein-protein interactions. These results suggest that vg is directly involved in determining which thoracic imaginal disc cells will form wings and halteres, perhaps by interacting with other nuclear regulatory proteins.

Alleles↗
PubMed1991

Regulation of achaete-scute gene expression and sensory organ pattern formation in the Drosophila wing.

Adult Drosophila possess a large number of sensory organs, including large and small bristles and other types of sensilla, each arising from a single mother cell at particular positions in a reproducible pattern. Genetic studies have shown that sensory organ pattern formation is partly coordinated by a number of structurally similar, potential heterodimer-forming, helix-loop-helix (HLH) regulatory proteins. Here, by localizing regulatory gene expression during the development of normal and mutant imaginal discs, we show that two positive regulators of sensory neurogenesis, the proneural achaete and scute proteins, initially trans-activate each other and are transiently expressed in identical patterns, including clusters of wing ectodermal cells and the individual sensory mother cells that arise from them. Two negative regulators, hairy and extramacrochaete, suppress sensory neurogenesis by selectively repressing achaete and scute gene expression, respectively, but in different spatial domains and at different developmental stages. Surprisingly, we also find that the level of achaete-scute activity influences the level of hairy expression, thereby providing feedback control upon achaete-scute activity and sensory organ formation. Some or all of these interactions may involve specific dimerization reactions between different combinations of HLH proteins.

Animals↗
PubMed1991

hairy gene function in the Drosophila eye: normal expression is dispensable but ectopic expression alters cell fates.

The regulatory gene hairy is expressed and required during early embryogenesis to control segmentation gene expression properly and during larval and pupal development to control the pattern of certain adult sensory structures. We have found the hairy protein to be expressed transiently during two stages of eye imaginal disc development, including all cells immediately anterior to the morphogenetic furrow that traverses the developing eye disc, and again in the presumptive R7 photoreceptor cells of the developing ommatidia. This pattern is conserved in a significantly diverged Drosophila species. We show that, surprisingly, ommatidia formed by homozygous hairy- mutant clones are apparently normal, indicating that hairy function in the eye is dispensable. However, we do find that ectopic expression of hairy causes numerous structural abnormalities and the alteration of cell fates. Thus, proper regulation of hairy is still essential for normal eye development. We suggest that the loss of hairy function may be compensated by other regulatory proteins, as has been observed previously for several structurally and functionally related genes involved in sensory organ development. The effects of ectopic hairy expression may result from interactions with proneural genes involved in the development of the eye and other sensory organs.

Animals↗
PubMed1990

Zebra patterns in fly embryos: activation of stripes or repression of interstripes?

Like Gould's zebra, the striped embryo can be viewed as a pattern of both interstripe repression and stripe activation. A growing body of evidence suggests that both processes are at work in regulating pair-rule gene expression. Certain genes, such as ftz, are largely negatively regulated in the interstripes through proximal upstream elements by the striped expression of other pair-rule genes, while others, such as hairy and eve, are largely regulated through distal upstream elements by the aperiodic gap genes (Figure 7). Different gap proteins control different subsets of stripes and interstripes. Combinations of gap proteins regulate transcription by binding to far upstream elements that contain different numbers and types of binding sites.

Animals↗
PubMed1990

Rattlesnake and scorpion antivenoms from the egg yolks of immunized hens.

Antivenoms used to treat poisonous bites and stings are usually derived from horse sera. Consequently, they contain horse immunoglobulins, which frequently cause complement mediated side effects, and other proteins that can cause serum sickness and, occasionally, anaphylactic shock. Here we describe a new, avian source of antivenoms that precludes these complications, and an efficient and gentle means for preparing antivenoms composed solely of venom-specific antibodies. We demonstrate that antivenoms purified from the egg yolks of laying hens immunized with Crotalus atrox rattlesnake venom and Leiurus quinquestriatus hebraeus scorpion venom neutralize the lethal effects of these venoms in vivo. Antivenoms purified from chicken eggs may be pharmaceutically safer and more economical to produce than current horse antivenoms.

Animals↗