The Drosophila endocycle is controlled by Cyclin E and lacks a checkpoint ensuring S-phase completion.

Early during Drosophila oogenesis the 16 interconnected cells of each germ-line cyst choose between two alternative fates. The single future oocyte enters meiosis, arrests, and becomes transcriptionally quiescent. The remaining 15 cells initiate a series of polyploid cell cycles to prepare for their role as nurse cells.

Bone morphogenetic proteins in development.

The bone morphogenetic proteins (BMPs) constitute a large family of cytokines related to members of the transforming growth factor-beta superfamily. Recent evidence, in particular from gene targeting experiments in the mouse, indicates that BMPs are required for mesoderm formation and for the development and patterning of many different organ systems. Significant progress has also been made in understanding the role of BMPs in gastrulation and neurulation in Xenopus and in identifying genes regulating BMP expression and components of the downstream signaling pathways.

Gene disruptions using P transposable elements: an integral component of the Drosophila genome project.

Biologists require genetic as well as molecular tools to decipher genomic information and ultimately to understand gene function. The Berkeley Drosophila Genome Project is addressing these needs with a massive gene disruption project that uses individual, genetically engineered P transposable elements to target open reading frames throughout the Drosophila genome. DNA flanking the insertions is sequenced, thereby placing an extensive series of genetic markers on the physical genomic map and associating insertions with specific open reading frames and genes.

Identification and behavior of epithelial stem cells in the Drosophila ovary.

Throughout their lives, adult Drosophila females continuously produce oocytes, each surrounded by an epithelial monolayer of follicle cells. To characterize the somatic stem cells that give rise to ovarian follicle cells, we marked dividing cells using FLP-catalyzed mitotic recombination and analyzed the resulting clones. Each ovariole in young females contains, on average, two somatic stem cells located near the border of germarium regions 2a and 2b.

cAMP regulates gastrin gene expression.

Gastrin is one of the most potent regulators of acid secretion and gastrointestinal cell growth. A variety of signals regulate gastrin release from the antral G cell. However, whether these secretagogues also stimulate gastrin gene expression has not been established.

The Drosophila salivary gland chromocenter contains highly polytenized subdomains of mitotic heterochromatin.

Peri-centromeric regions of Drosophila melanogaster chromosomes appear heterochromatic in mitotic cells and become greatly underrepresented in giant polytene chromosomes, where they aggregate into a central mass called the chromocenter. We used P elements inserted at sites dispersed throughout much of the mitotic heterochromatin to analyze the fate of 31 individual sites during polytenization. Analysis of DNA sequences flanking many of these elements revealed that middle repetitive or unique sequence DNAs frequently are interspersed with satellite DNAs in mitotic heterochromatin.

Fusome asymmetry and oocyte determination in Drosophila.

Germline cysts containing 16 interconnected cells (cystocytes) are produced at an early stage of Drosophila oogenesis by progenitor cells known as cystoblasts that undergo four synchronous rounds of incomplete division. During cyst formation, a region of specialized, spectrin-rich cytoplasm called the fusome traverses the intercellular connections (ring canals), linking individual cystocytes. Subsequently, 15 cystocytes begin to transport specific RNAs and other components into the remaining cell, the future oocyte.

A transposable element can drive the concerted evolution of tandemly repetitious DNA.

Recombination and conversion have been proposed to drive the concerted evolution of tandemly repeated DNA sequences. However, specific correction events within the repeated genes of multicellular organisms have not been observed directly, so their nature has remained speculative. We investigated whether the excision of transposable P elements from tandemly repeated sequences would induce unequal gene conversion.

Insertional mutagenesis of Drosophila heterochromatin with single P elements.

Insertional mutagenesis with transposable P elements has greatly facilitated the identification and analysis of genes located throughout the 70% of the Drosophila melanogaster genome classified as euchromatin. In contrast, genetically marked P elements have only rarely been shown to transpose into heterochromatin. By carrying out single P element insertional mutagenesis under conditions where position-effect variegation was suppressed, we efficiently generated strains containing insertions at diverse sites within centromeric and Y-chromosome heterochromatin.

Cloning of the human glycine transporter type 1: molecular and pharmacological characterization of novel isoform variants and chromosomal localization of the gene in the human and mouse genomes.

We report the molecular cloning of a cDNA encoding a high affinity human glycine transporter. An open reading frame of 1914 nucleotides encodes a 638-amino acid protein that transports glycine in a Na+/Cl(-)-dependent manner. In common with other Na+/Cl(-)-dependent transporters, it possesses 12 putative transmembrane domains, according to its hydropathicity profile.

The Drosophila fusome, a germline-specific organelle, contains membrane skeletal proteins and functions in cyst formation.

Oogenesis in Drosophila takes place within germline cysts that support polarized transport through ring canals interconnecting their 15 nurse cells and single oocyte. Developing cystocytes are spanned by a large cytoplasmic structure known as the fusome that has been postulated to help form ring canals and determine the pattern of nurse cell-oocyte interconnections. We identified the adducin-like hts product and alpha-spectrin as molecular components of fusomes, discovered a related structure in germline stem cells and documented regular associations between fusomes and cystocyte centrosomes.

Characterization of an atypical member of the Na+/Cl(-)-dependent transporter family: chromosomal localization and distribution in GABAergic and glutamatergic neurons in the rat brain.

A 3.7-kb cDNA fragment, designated rat-XT1, was isolated from a rat whole-brain cDNA library. The nucleotide sequence of XT1 codes for a 727 amino acid protein with a calculated molecular mass of 81,139 Da and 12 putative transmembrane domains.

Transposable elements and the evolution of heterochromatin.

Drosophila P elements were shown to insert frequently into telomeric and centromeric heterochromatin, and to prefer a region associated with efficient copy number regulation. Upon excision, P elements frequently altered the number of repeats in a tandem array of heterochromatic sequences, by inducing unequal gene conversion. These studies suggest that a flux of transposable element insertions and excisions has the capacity to rapidly and nonrandomly modify heterochromatic sequences dispersed at multiple chromosomal sites.

Germline stem cell division and egg chamber development in transplanted Drosophila germaria.

Germline and somatic stem cells reside within the anterior region (or "germarium") of each ovariole in the Drosophila ovary. When individual germaria were dissected free of developing eggs and sheath tissue and transplanted into the abdominal cavity of a host fly, they regenerated ovariole-like structures and continuously supported the entire process of oogenesis, indicating that the stem cells remained functional. This system allowed us to measure the duration of several stages in oogenesis and to analyze the role of specific germarial cells in providing stem cell function.

Efficient and dispersed local P element transposition from Drosophila females.

We have investigated how Drosophila P element insertions are distributed in the chromosomal region near their starting site. A single P element residing in the euchromatin of minichromosome Dp1187 was mobilized following a cross to the delta 2-3 (99B) strain, and progeny bearing transpositions were identified with a minimum of bias by performing Southern blots on progeny. Approximately 1-2% of all progeny minichromosomes contained new insertions.

Preferential transposition of Drosophila P elements to nearby chromosomal sites.

Two different schemes were used to demonstrate that Drosophila P elements preferentially transpose into genomic regions close to their starting sites. A starting element with weak rosy+ marker gene expression was mobilized from its location in the subtelomeric region of the 1,300-kb Dp1187 minichromosome. Among progeny lines with altered rosy+ expression, a much higher than expected frequency contained new insertions on Dp1187.

A new tool for investigating G protein-coupled receptors.

Vertebrate olfactory receptors are members of the seven-transmembrane-domain G protein-coupled receptor family. They utilize intracellular signal transduction pathways which are activated by stimulation of odorant receptors and use the second messengers cAMP and/or inositol 1,4,5-trisphosphate and diacylglycerol. Studies of how odorants bind to and activate the receptors can be considered part of the more general problem of how chemicals interact with G protein-coupled receptors.

Replication forks are not found in a Drosophila minichromosome demonstrating a gradient of polytenization.

Differential DNA replication is widely held to influence polytene chromosome structure by causing the dramatic reductions in heterochromatic DNA content that are characteristic of most endopolyploid cells. The "underreplication model" of heterochromatic sequence underrepresentation predicts that replication intermediates should populate regions of DNA between fully polytenized euchromatic sequences and underpolytenized heterochromatic sequences. We directly tested this prediction using Dp1187, a 1300 kb Drosophila minichromosome containing well-defined heterochromatic regions.

Identification, characterization, and molecular cloning of a novel transporter-like protein localized to the central nervous system.

During the course of large scale purification of the D1 dopamine receptor from rat brain, a protein of approximately 87,000 daltons (p87) was observed to copurify with the D1 receptor through four chromatographic steps. To characterize the nature of this protein, bovine and rat cDNA clones were isolated and sequenced. The bovine and rat clones were highly conserved (98.

Analysis of subtelomeric heterochromatin in the Drosophila minichromosome Dp1187 by single P element insertional mutagenesis.

We investigated whether single P element insertional mutagenesis could be used to analyze heterochromatin within the Drosophila minichromosome Dp1187. Forty-five insertions of the P[lacZ,rosy+] element onto Dp1187 (recovered among 7,825 transpositions) were highly clustered. None was recovered in centromeric heterochromatin, but 39 occurred about 40 kb from the distal telomere within a 4.

The gene encoding the small nuclear ribonucleoprotein-associated protein N is expressed at high levels in neurons.

The highly homologous small nuclear ribonucleoprotein-associated proteins of the Sm group, human N and B/B', are derived from distinct, but similar genes. While the almost identical structural organization of the genes for N and B/B' suggests that they emerged from a common ancestral gene via a duplication event, they now reside on different chromosomes. In contrast to B (which is expressed in all tissues examined) and B' (which is widely expressed with the notable exception of the brain), results from in situ hybridization experiments showed that N is found predominantly in central neurons.