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F R Turner

Publications and source records attributed to F R Turner.

34 records · Page 2Linked to original sources
PubMed1987

A development genetic analysis of the gene regulator of postbithorax in Drosophila melanogaster.

We report the characterization of loss-of-function alleles of the homoeotic mutation Regulator of postbithorax (Rg-pbx) in Drosophila melanogaster. Rg-pbx is a dominant gain-of-function mutation which shows a transformation of posterior haltere to wing in the adult cuticle. This mutant phenotype mimics that of the bithorax complex lesion postbithorax (pbx). Loss-of-function alleles described here are lethal in the embryonic stage and affect the pattern of segmentation of the embryo. Examination of the terminal phenotype of null and hypomorphic alleles of Rg-pbx has shown that inactivation of the Rg-pbx gene leads to loss of the thoracic segments and the adjacent labial segment of the Drosophila embryo. An effect of the mutations is also seen in the seventh and eighth abdominal segments of embryos. The loss-of-function phenotype is similar to that described for the segmentation mutant hunchback (hb). Complementation tests show that Rg-pbx and hb are allelic. Temperature shift experiments using a temperature-sensitive loss-of-function allele show that the Rg-pbx gene product is required early in embryogenesis. We further report that the dominant Rg-pbx phenotype is sensitive to the gene dosage of another segmentation-controlling gene, fushi tarazu (ftz). Flies carrying a mutant copy of the ftz gene in trans to Rg-pbx show a dramatic enhancement of the penetrance of the homoeotic mutant phenotype. We were also able to demonstrate a suppression of the Rg-pbx phenotype by the addition of a duplication for the ftz+ gene to an Rg-pbx stock. Examination of the phenotype of ftz Rg-pbx- double-mutant embryos did not reveal a clear pattern of epistasis between the genes nor was absolute additivity of phenotype seen. A possible formal relationship between Rg-pbx, ftz, and the postbithorax (pbx) locus is proposed.

Abdomen↗
PubMed1987

A genetic and developmental analysis of mutations in the Deformed locus in Drosophila melanogaster.

Individuals expressing recessive mutations in the Deformed (Dfd) locus of Drosophila melanogaster were examined for embryonic and adult defects. Mutant embryos were examined in both scanning electron microscope and light microscope preparations. The adult Dfd recessive mutant phenotype was assessed in somatic clones and in survivors homozygous for hypomorphic alleles of the gene. The time of Dfd+ action was determined by studying a temperature conditional allele. Dfd+ is required in three embryonic cephalic segments to form a normal head. Mutant embryos of Dfd display defects in derivatives of the maxillary segment, of the mandibular segment, and of some more anterior segments. In the adult fly, defects are seen in the posterior aspect of the head when the gene is mutant. A transformation from head to thoracic-like tissue is seen dorsally and a deletion of structures is seen ventrally. Shift studies utilizing a temperature conditional allele have shown that the gene product is necessary during at least two periods of development, during embryonic segmentation and head involution and during the late larval and pupal stages. From these studies we conclude that Dfd is a homeotic gene necessary for proper specification of both the embryonic and the adult head.

Alleles↗
PubMed1984

Defects in embryogenesis in mutants associated with the antennapedia gene complex of Drosophila melanogaster.

Embryogenesis in individuals with mutations or deficiencies of the genes in the polytene interval 84A-84B1,2 of Drosophila melanogaster was examined using scanning electron microscopy (SEM). The developmental function of this region of chromosome 3 is of particular interest since it contains the Antennapedia Gene Complex (ANT-C), a gene cluster that includes the homoeotic proboscipedia (pb), Sex combs reduced (Scr), and Antennapedia (Antp) loci. The results of SEM studies, clonal analyses, and temperature-shift experiments show that the fushi tarazu (ftz) and zerknullt (zen) genes, which map between pb and Scr, are involved in processes initiated during embryogenesis. The activity of ftz+ appears to be required within the first 4 hr of development for the establishment of the proper number of segments in the embryonic germ band. Individuals with ftz mutations or deficiencies produce only half the normal number of segments. Each of the segments is twice the normal width and is apparently comprised of cells that would normally form two separate metameres. The zen allele is required from about 2-4 hr of embryogenesis. Mutations of this gene result in disturbances of morphogenetic movements during gastrulation. The mutant phenotype is characterized by the absence of the optic lobe, defects in involution of the head segments, and in some cases, failure of germ band elongation. A requirement during embryogenesis for the activities of other genes residing in the 84A-84B1,2 polytene interval is suggested by the phenotypes of individuals heterozygous or homozygous for chromosomal deficiencies. Using the deficiencies Df(3R)AntpNs+R17, Df(3R)Scr, and Df(3R)ScxW+RX2, we examined the effects of deleting the distal portions or all of the 84A-84B1,2 interval. The defects in deletion heterozygotes suggest that the wild-type activity of some gene(s) other than zen, within or just adjacent to the 84B1,2 doublet, is required to complete normal head involution. The deletion of all the loci in the 84A5-84B1,2 interval results in grossly abnormal morphology and morphogenesis of the gnathocephalic appendages of the embryo. From these studies we conclude that mutations and deficiencies of genes associated with the ANT-C have profound effects on embryogenesis. The mutant phenotypes suggest, in addition to ensuring proper segment identity, the wild-type alleles of the 84A-84B1,2 genes are necessary for normal segmentation and elongation of the germ band and normal head involution.

Animals↗
PubMed1976

Interspecific transplantation of polar plasm between Drosophila embryos.

Posterior polar plasm of the Drosophila egg has been shown to function autonomously in germ cell determination after transplantation to either the anterior or mid-ventral region of the early embryo. By means of similar transplantations, we have tested the ability of polar plasm of Drosophila immigrans to induce the formation of pole cells in a Drosophila melanogaster embryo. After the transplantation of polar plasm, "hybrid" pole cells were found in which both pole cell-specific organelles, the polar granules and nuclear body, were structurally similar to those characteristic of the transplanted cytoplasm. In order to determine whether these hybrid cells can function as germ cell precursors, these cells were transplanted to the posterior tip of genetically marked embryos. Approximately 5% of the flies obtained from embryos receiving potential pole cells produce offspring derived from the induced pole cells. This result demonstrates that polar plasm can function in interspecific species combinations and indicates that the molecular mechanisms of germ cell determination are conservative in evolution. Finally, in order to test whether there is any evidence for cytoplasmic inheritance of polar granules, embryos derived from hybrid pole cells were examined for their polar granule morphology. The fine structure of the granules conformed to that of the nucleus. Thus, no evidence was found for the cytoplasmic inheritance of these particular organelles.

Animals↗
PubMed1975

Cytoplasmic microtubule proteins of the embryo of Drosophila melanogaster.

We have been able to purify, in bulk, the cytoplasmic microtubule proteins of eggs and embryos of Drosophila melanogaster by means of in vitro self-assembly of microtubules from subunits present in a high-speed supernatant fraction of eggs or embryos. This provides the first successful application of this method to purification of microtubule protein from a source other than vertebrate brain, and the first purification of insect microtubule proteins. Our electron micrographs show that the in vitro assembled microtubules are morphologically typical and apparently are comprised of the expected 13 protofilaments. The protein we obtain from such preparations binds [3H]colchicine and has a sedimentation value of 6.4 S-6.9 S which is close to the predicted value for microtubule protein dimer. Both alpha- and beta-microtubule proteins are evident in sodium dodecyl sulfate polyacrylamide electropherograms of the isolated proteins. The apparent molecular weights of these species on dodecyl sulfate polyacrylamide gels are 54,000 and 52,000, respectively. These values as well as the amino acid composition and N-terminal methionine of the Drosophilia proteins are very closely comparable to microtubule proteins from other, unrelated organisms.

Amino Acids↗
PubMed1972

Growth, cell division, and fragmentation in a species of Flexibacter.

Flexibacter FS-1, a gram-negative gliding bacterium was grown in liquid culture as long (over 100-mum) filaments. The filaments possessed a triple-track wall which resembled that found in other gram-negative bacteria. Although phase-contrast microscopy indicated that the long filaments were nonseptate, electron microscopy revealed three or four septa along the length of each filament. The septa contained lysozyme-sensitive, electron-opaque material, presumed to be peptidoglycan, sandwiched between cell membranes. The outer triple track wall was not part of the septum. Mesosomes were seen in various areas of the cell and frequently were observed attached to septa in different stages of completion. Studies of the organism in slide culture revealed that individual filaments grew in an exponential fashion and divided in the middle despite the long length and multiseptate condition. When the temperature of a liquid culture growing exponentially with a generation time of 90 minutes was shifted from 30 to 35 C, the filaments fragmented into three or four shorter cells within 120 min. The short cells continued to grow exponentially at 35 C at approximately the same rate as at 30 C. When the culture was shifted back to 30 C, the cells immediately stopped dividing and began to elongate. After a period of 2 to 3 hr, cell division resumed. It is suggested that the shift-up in temperature induced the completion of the cross wall (centripetal growth of the triple-track wall) and cell separation at the sites of previously formed septa, whereas the shift-down in temperature caused a transient inhibition of cross-wall formation but not of growth. Fragmentation was inhibited by sodium azide but took place despite the inhibition of protein synthesis by chloramphenicol or the inhibition of deoxyribonucleic acid synthesis by mitomycin C.

Azides↗
PubMed1970

The effects of colchicine on spermatogenesis in Nitella.

Treatment of Nitella antheridia with colchicine results in various sperm abnormalities, depending upon duration of exposure and subsequent recovery. Early effects of treatment include disappearance of spindle fibers and a cessation of ordered cell wall formation in dividing cells. Sperm released from antheridia treated for 24 hr and allowed to recover for 4-5 days possess branched flagella. After a recovery period of 6-10 days the sperm appear normal; however, following longer recovery periods, the sperm exhibit variations in size and number of flagella. Branched flagella contain a variety of microtubule patterns ranging from branches containing a single microtubule to flagella with an excess of microtubules. Spermatids which differentiate in the presence of colchicine lack flagella and a microtubular sheath. Nuclear contents undergo condensation stages; however, the nucleus as a whole does not undergo the orderly elongation and coiling characteristic of untreated Nitella spermatids. Long-term colchicine treatment followed by a recovery period produces atypical microtubules and microtubular aggregations in the spermatid. The results indicate that colchicine affects not only polymerization of microtubule subunits but also factors responsible for their ordered spatial relationships in the cell. The presence of microtubules is a prerequisite for normal morphological changes during spermiogenesis.

Chromosomes↗
PubMed1968

An ultrastructural study of plant spermatogenesis. Spermatogenesis in Nitella.

Spermatogenesis in the charophyte Nitella has been followed in antheridia prepared for light and electron microscopy. The antheridial filament cells contain paired centrioles which are similar in structure and behavior to the centrioles of animal cells. In the early spermatid, the centrioles undergo an initial elongation at their distal ends and become joined by a spindle-shaped fibrous connection. At the same time, their proximal ends are closely associated with the development of a layer of juxtaposed microtubules which will form the microtubular sheath. The architectural arrangement of these microtubules suggests that they constitute a cytoskeletal system, forming a framework along which the mitochondria and plastids become aligned and along which the nucleus undergoes extensive elongation and differentiation. The microtubular sheath persists in the mature sperm. During mid-spermatid stages, the centrioles give rise to the flagella and concomitantly undergo differentiation to become the basal bodies. The Golgi apparatus goes through a period of intensive activity during mid-spermatid stages, then decreases in organization until it can no longer be detected in the late spermatid. An attempt is made to compare similarities between plant and animal spermiogenesis.

Cell Differentiation↗