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J W Posakony

Publications and source records attributed to J W Posakony.

At least 19 recordsLinked to original sources
PubMed1992

Suppressor of Hairless, the Drosophila homolog of the mouse recombination signal-binding protein gene, controls sensory organ cell fates.

Suppressor of Hairless (Su(H)) is required at two stages of adult sensory organ development in Drosophila. Complete loss of Su(H) function results in a "neurogenic" phenotype in imaginal discs, in which too many cells adopt the sensory organ precursor cell fate. Su(H) is also involved in controlling the fates of sensillum accessory cells and is specifically expressed in two of these cells. Su(H) is the Drosophila homolog of the mouse J kappa RBP gene, whose product binds specifically to the recombination signal sequence of immunoglobulin J kappa segments. The Su(H) and J kappa RBP proteins are 82% identical over most of their length, and share with bacteriophage integrates and yeast recombinases a motif that includes residues directly involved in catalyzing recombination.

Amino Acid Sequence↗
PubMed1992

Spatial regulation of proneural gene activity: auto- and cross-activation of achaete is antagonized by extramacrochaetae.

The spatially restricted activities of achaete (ac) and scute (sc) are thought to define proneural clusters of potential sensory organ precursor cells in the imaginal discs of Drosophila. These genes encode transcriptional regulators of the basic helix-loop-helix (bHLH) class. We have found that 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 pattern and that autoactivation 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 inhibitory HLH protein encoded by the extramacrochaetae (emc) gene. We have found that emc is expressed in the wing imaginal disc in a pattern strongly complementary to that of the proneural clusters. Our results indicate that emc plays an essential early role in defining territories of bristle-forming potential.

Animals↗
PubMed1992

The Drosophila gene Hairless encodes a novel basic protein that controls alternative cell fates in adult sensory organ development.

The mechanosensory bristles of adult Drosophila are composed of four cells that, in most cases, are progeny of a single sensory organ precursor (SOP) cell. Two sister cells in this lineage, the trichogen and tormogen, produce the external shaft and socket of the bristle, respectively. Loss-of-function mutations of Hairless (H) confer two distinct mutant phenotypes on adult bristles. The bristle loss phenotype results from the failure to specify and/or execute the SOP cell fate; the double socket phenotype results from the transformation of the trichogen (shaft) cell into a second tormogen (socket) cell. We have found that the H gene encodes a novel basic protein with a predicted molecular mass of 109 kD. Basal levels of expression of a transgene (P[Hs-H]) in which the H protein-coding region is under the control of the Hsp70 promoter are sufficient to provide full rescue of H mutant phenotypes. Heat shock treatment of P[Hs-H] transgenic animals as late larvae and early pupae produces a tormogen-to-trichogen (double shaft) cell fate transformation, as well as bristle multiplication and loss phenotypes very similar to those caused by loss-of-function mutations in the neurogenic gene Notch. Our results indicate that the SOP cell fate requires H to antagonize the activity of the neurogenic group of genes and that the expression of distinct cell fates by the trichogen/tormogen sister cell pair depends on an asymmetry in their levels of H+ activity or in their thresholds for response to H.

Amino Acid Sequence↗
PubMed1991

Hairless is required for the development of adult sensory organ precursor cells in Drosophila.

Reduction of the wild-type activity of the gene Hairless (H) results in two major phenotypic effects on the mechanosensory bristles of adult Drosophila. Bristles are either 'lost' (i.e. the shaft and socket fail to appear) or they exhibit a 'double socket' phenotype, in which the shaft is apparently transformed into a second socket. Analysis of the phenotypes conferred by a series of H mutant genotypes demonstrates (1) that different sensilla exhibit different patterns of response to decreasing levels of H+ function, and (2) that the 'bristle loss' phenotype results from greater loss of H+ function than the 'double socket' phenotype. The systematic study of H allelic combinations enabled us to identify genotypes that reliably produce specific mutant defects in particular positions on the bodies of adult flies. This permitted us to investigate the cellular development of sensilla in these same positions in larvae and pupae and thereby establish the developmental basis for the mutant phenotypes. We have found that H is required for at least two steps of adult sensillum development. In positions where 'double socket' microchaetes appear on the notum of H mutant flies, sensillum precursor cells are present in the developing pupa and divide normally, but their progeny adopt an aberrant spatial arrangement and fail to differentiate correctly. In regions of the notum exhibiting 'bristle loss' in adult H mutants, we were unable at the appropriate stages of development to detect sensillum-specific cell types, the precursor cell divisions that generate them, or the primary precursor cells themselves. Thus, the H 'bristle loss' phenotype appears to reflect a very early defect in sensillum development, namely the failure to specify and/or execute the sensory organ precursor cell fate. This finding indicates that H is one of a small number of identified genes for which the loss-of-function phenotype is the failure of sensillum precursor cell development.

Alleles↗
PubMed1991

The Drosophila extramacrochaetae protein antagonizes sequence-specific DNA binding by daughterless/achaete-scute protein complexes.

In Drosophila, a group of regulatory proteins of the helix-loop-helix (HLH) class play an essential role in conferring upon cells in the developing adult epidermis the competence to give rise to sensory organs. Proteins encoded by the daughterless (da) gene and three genes of the achaete-scute complex (AS-C) act positively in the determination of the sensory organ precursor cell fate, while the extramacrochaetae (emc) and hairy (h) gene products act as negative regulators. In the region upstream of the achaete gene of the AS-C, we have identified three 'E box' consensus sequences that are bound specifically in vitro by hetero-oligomeric complexes consisting of the da protein and an AS-C protein. We have used this DNA-binding activity to investigate the biochemical basis of the negative regulatory function of emc. Under the conditions of our experiments, the emc protein, but not the h protein, is able to antagonize specifically the in vitro DNA-binding activity of da/AS-C and putative da/da protein complexes. We interpret these results as follows: the heterodimerization capacity of the emc protein (conferred by its HLH domain) allows it to act in vivo as a competitive inhibitor of the formation of functional DNA-binding protein complexes by the da and AS-C proteins, thereby reducing the effective level of their transcriptional regulatory activity within the cell.

Animals↗
PubMed1990

extramacrochaetae, a negative regulator of sensory organ development in Drosophila, defines a new class of helix-loop-helix proteins.

The function of the extramacrochaetae (emc) gene is required to establish the normal spatial pattern of adult sensory organs in Drosophila. emc acts to suppress sensory organ development in certain regions of the body surface, apparently by antagonizing the function of the achaete and scute genes of the achaetescute complex (AS.C). We have found that emc encodes a novel member of the helix-loop-helix (HLH) family of proteins. The emc protein shares the dimerization domain of other HLH proteins but lacks their DNA binding motif. We propose a model in which the emc protein negatively regulates sensory organ determination by forming heterodimers with the HLH proteins encoded by the AS-C and/or daughterless, thereby altering or interfering with their activity.

Alleles↗
PubMed1990

A dual function of the Notch gene in Drosophila sensillum development.

We have investigated the function of the neurogenic gene Notch (N) during development of the adult sensilla of Drosophila. Heat pulses were applied to flies carrying the temperature-sensitive Notch allele Nts1 at different larval and pupal stages. We can show that the reduction of Notch+ function during a short interval prior to the onset of sensillum precursor division, resulting from a heat pulse between 0 and 14 hr after puparium formation (apf), leads to an increase in microchaete precursors at the expense of epidermal cells. The structure and cellular composition of the sensilla produced by these supernumerary precursors are normal. Later heat pulses which include the interval immediately after sensillum precursor division (14-20 hr apf) lead, among the progeny of the sensillum precursors, to a hyperplasia of sensory neurons, at the expense of accessory cells. The resulting "sensilla" consist of neurons only and lack the external cuticular structures (i.e., shaft, socket). These results demonstrate that similar mechanisms both of which involve the function of the Notch gene may be operating to sort out (premitotic) sensillum precursors from epidermal precursors and (postmitotic) sensory neurons from accessory cells. They further show that in postmitotic sensillum cells the differentiative fate is not yet irreversibly fixed, but presumably requires cell-cell interaction to become established.

Alleles↗
PubMed1990

Sensillum development in the absence of cell division: the sensillum phenotype of the Drosophila mutant string.

We have investigated sensillum development in Drosophila embryos homozygous for mutations in the locus string (stg). In these embryos, cell division is blocked following blastoderm formation. This permits a study of the differentiative fate of undivided precursor cells, in particular those giving rise to the larval sensory organs (sensilla). Of the different cell fates normally represented in the sensilla (i.e., sensory neuron, thecogen cell, trichogen cell, tormogen cell, glia cell), only the phenotype of sensory neurons is expressed morphologically in stg embryos, suggesting that the neuronal fate predominates over the fates of the nonneuronal accessory cells. Consistent with this finding, the P element-lacZ insertion A1-2nd-29, which is a marker for trichogen and tormogen cells in the wild-type embryo, is not expressed in the body wall of the stg embryo. Some sensillum precursor cells appear to express a mixed fate in stg mutants: They express antigens (recognized by the monoclonal antibodies 22C10 and 21A6) which in the wild-type appear in separate cells (sensory neurons and thecogen cell, respectively). The differentiation of undivided cells in stg embryos is not restricted to the peripheral nervous system; in all types of tissues analyzed in this study (e.g., epidermis, intestine, muscle, CNS), precursor cells express characteristics normally exhibited by their progeny.

Animals↗
PubMed1989

Development of adult sensilla on the wing and notum of Drosophila melanogaster.

We have investigated the temporal pattern of appearance, cell lineage, and cytodifferentiation of selected sensory organs (sensilla) of adult Drosophila. This analysis was facilitated by the discovery that the monoclonal antibody 22C10 labels not only the neuron of the developing sensillum organ, but the accessory cells as well. The precursors of the macrochaetes and the recurved (chemosensory) bristles of the wing margin divide around and shortly after puparium formation, while those of the microchaetes and the stout and slender (mechanosensory) bristles of the wing margin divide between 9 h and 18 h after puparium formation (apf). The onset of sensillum differentiation follows the terminal precursor division within a few hours. Four of the cells in an individual microchaete organ are clonally related: A single first-order precursor cell divides to produce two second-order precursors; one of these divides into the neuron and thecogen cell, the other into the trichogen cell and tormogen cell. Along the anterior wing margin, two rounds of division generate the cells of the mechanosensory sensilla; here, no strict clonal relationship seems to exist between the cells of an individual sensillum. At the time of sensillum precursor division, many other, non-sensillum-producing cells within the notum and wing proliferate as well. This mitotic activity follows a spatially non-random pattern.

Animals↗
PubMed1988

The Drosophila gene knirps-related is a member of the steroid-receptor gene superfamily.

Molecular cloning has demonstrated that the receptors for steroid, retinoid and thyroid hormones are part of a large superfamily of nuclear regulatory proteins. In vertebrates these molecules regulate diverse biological processes such as pattern formation, cellular differentiation and homeostasis. The universal necessity for embryonic and adult cells to respond to their external environment might mean that members of this family pre-date the divergence of vertebrates and invertebrates. We have screened a Drosophila genomic library for steroid receptor homologues using a human retinoic acid receptor complementary DNA as a hybridization probe. Several clones were recovered, one of which mapped to chromosomal position 77E1-2, the cytological location of the gap segmentation gene knirps. Sequence analysis of a cDNA clone representing the human retinoic acid receptor homologue showed similarity of the predicted protein to the vertebrate steroid receptors, as well as to the predicted knirps gene product. In situ hybridization of a cDNA probe to wild-type embryos revealed a uniform distribution of transcripts that were apparently maternally derived. Zygotic transcript accumulation begins in a broad anteroventral domain before the cellular blastoderm stage. At the cellular blastoderm stage two additional circumferential bands of transcript appear.

Amino Acid Sequence↗
PubMed1983

Interspersed sequence organization and developmental representation of cloned poly(A) RNAs from sea urchin eggs.

A random primed complementary DNA (cDNA) clone library constructed from total maternal poly(A) RNA of sea urchin eggs was screened with two cloned genomic repetitive sequence probes. Sets of cDNA clones reacting with each of these repetitive sequences were recovered. Most of the cloned transcripts included both single copy and repeat sequence elements. Except for the shared repeat sequence element, both the repetitive and single copy regions of the members of each set of clones failed to crossreact. Single copy probes linked to the repeats on the cloned maternal RNAs are represented in an asymmetric manner. It follows that many different genomic members of a given dispersed repeat sequence family are represented in the maternal RNA. RNA gel blots carried out with several repeat probes display about 10 to 20 prominent maternal poly(A) RNAs containing transcripts of each repetitive sequence family. The interspersed maternal transcripts are 3000 to 15,000 bases in length. Maternal transcripts reacting with single copy probes derived from the cloned cDNAs persist during embryonic development, and in some cases appear to be augmented by similar, newly synthesized embryo transcripts. Two examples were found in which additional transcripts of different length appear at specific developmental stages. The transcribed single copy regions are highly polymorphic in the genomes of different individual sea urchins, and comparisons of closely related sea urchin species showed that both the prevalence and length of specific maternal transcripts change rapidly during evolution. Nucleotide sequences of two homologous repeat elements occurring on different cloned transcripts displayed translation stop codons in every possible reading frame. These repeat sequences display structural features suggesting that there has been evolutionary transposition into transcription units active during oogenesis. The repeat elements and their flanking single copy regions reside either in very long 3' or 5'-terminal sequences, or in unprocessed intervening sequences in the maternal poly(A) RNA. These findings lead us to the proposal that the majority of the cytoplasmic poly(A) RNA in echinoderm eggs and early embryos is similar in form to RNAs that occur in the nucleus rather than to the messenger RNA of later cells.

Animals↗
PubMed1983

Transcripts of three mitochondrial genes in the RNA of sea urchin eggs and embryos.

cDNA clones representing mitochondrial 16 S rRNA, and mRNAs for cytochrome oxidase I and an unidentified reading frame were used to measure the prevalence and stability of these transcripts in gastrula stage embryos. The 16 S rRNA is the most prevalent embryo poly(A) RNA, and is synthesized about four times more rapidly than is the mRNA for cytochrome oxidase. The relative prevalence of the two mRNAs is largely determined by their turnover rates.

Animals↗
PubMed1983

Correct developmental expression of a cloned alcohol dehydrogenase gene transduced into the Drosophila germ line.

We have used P-element-mediated transformation to introduce a cloned Drosophila alcohol dehydrogenase (Adh) gene into the germ line of ADH null flies. Six independent transformants expressing ADH were identified by their acquired resistance to ethanol. Each transformant carries a single copy of the cloned Adh gene in a different chromosomal location. Four of the six transformant lines exhibit normal Adh expression by the following criteria: quantitative levels of ADH enzyme activity in larvae and adults; qualitative tissue specificity; the size of stable Adh mRNA; and the characteristic developmental switch in utilization of two different Adh promoters. The remaining two transformants express ADH enzyme activity with the correct tissue specificity, but at a lower level than wild type. These results demonstrate that an 11.8 kb chromosomal fragment containing the Adh gene includes the cis-acting sequences necessary for its correct developmental expression, and that a variety of chromosomal sites permit proper Adh gene function.

Alcohol Dehydrogenase↗
PubMed1983

Comparison of sea urchin and human mtDNA: evolutionary rearrangement.

Clones of full-length mtDNA have been isolated from a Strongylocentrotus franciscanus recombinant DNA library by screening a cDNA clone of cytochrome oxidase subunit 1 mRNA. Restriction fragment cross-hybridization analysis shows the following difference in gene arrangement between sea urchin and human mtDNA. The 16S rRNA and cytochrome oxidase subunit 1 genes are directly adjacent in sea urchin mtDNA. These two genes are separated in human and other mammalian mtDNAs by the region containing unidentified reading frames 1 and 2. In spite of the difference in gene order, gene polarity appears to have been conserved. We conclude that the difference in gene order reflects a rearrangement that took place in the sea urchin lineage since sea urchins and mammals last shared a common ancestor.

Animals↗
PubMed1981

Molecular structure of maternal RNA.

The presence of a stable maternal mRNA population in mature oocytes of many species is well established. In this paper we show that the mature egg contains, in addition to these mature mRNAs, a structurally more complex population of RNA transcripts. This latter class of RNA consists of polyadenylated transcripts of repetitive and nonrepetitive DNA elements covalently linked into long interspersed molecules. As much as seventy percent of the polyadenylated egg RNA of Xenopus laevis and Strongylocentrotus purpuratus is represented in this interspersed population. Most of the nonrepetitive DNA sequences represented in the mature mRNA population are also present in the interspersed RNA. These transcripts have an organization similar to that of somatic cell nuclear RNA. Data are presented that suggests some of these interspersed maternal transcripts are unprocessed precursor-like molecules. Some possible functions of this novel class of RNA during early development are discussed.

Animals↗
PubMed1980

Evolutionary conservation of repetitive sequence expression in sea urchin egg RNA's.

Cloned repetitive DNA sequences were used to determine the number of homologous RNA transcripts in the eggs of two sea urchin species, Strongylocentrotus purpuratus and S. franciscanus. The eggs of these species contain different amounts of RNA, and their genomes contain different numbers of copies of the cloned repeats. The specific pattern of repetitive sequence representation in the two egg RNA's is nonetheless quantitatively similar. The evolutionary conservation of this pattern suggests the functional importance of repeat sequence expression.

Animals↗