Polytene chromosome

Last updated
Polytene chromosomes in a Chironomus salivary gland cell Flemming1882Tafel1Fig14.jpg
Polytene chromosomes in a Chironomus salivary gland cell
Polytene chromosome Polyten chromosome.jpg
Polytene chromosome

Polytene chromosomes are large chromosomes which have thousands of DNA strands. They provide a high level of function in certain tissues such as salivary glands of insects. [1]

Contents

Polytene chromosomes were first reported by E.G.Balbiani in 1881. Polytene chromosomes are found in dipteran flies: the best understood are those of Drosophila , Chironomus and Rhynchosciara . They are present in another group of arthropods of the class Collembola, a protozoan group Ciliophora, mammalian trophoblasts and antipodal, and suspensor cells in plants. [2] In insects, they are commonly found in the salivary glands when the cells are not dividing.

They are produced when repeated rounds of DNA replication without cell division forms a giant chromosome. Thus polytene chromosomes form when multiple rounds of replication produce many sister chromatids which stay fused together.

Polytene chromosomes, at interphase, are seen to have distinct thick and thin banding patterns. These patterns were originally used to help map chromosomes, identify small chromosome mutations, and in taxonomic identification. They are now used to study the function of genes in transcription. [3]

Function

In addition to increasing the volume of the cells' nuclei and causing cell expansion, polytene cells may also have a metabolic advantage as multiple copies of genes permits a high level of gene expression. In Drosophila melanogaster , for example, the chromosomes of the larval salivary glands undergo many rounds of endoreduplication to produce large quantities of adhesive mucoprotein ("glue") before pupation. Another example within the fly itself is the tandem duplication of various polytene bands located near the centromere of the X chromosome which results in the Bar phenotype of kidney-shaped eyes. [4] [5]

The interbands are involved in the interaction with the active chromatin proteins, nucleosome remodeling, and origin recognition complexes. Their primary functions are: to act as binding sites for RNA pol II, to initiate replication and, to start nucleosome remodeling of short fragments of DNA. [6]

Structure

In insects, polytene chromosomes are commonly found in the salivary glands; they are also referred to as "salivary gland chromosomes". The large size of the chromosome is due to the presence of many longitudinal strands called chromonemata; hence the name polytene (many stranded). They are about 0.5 mm in length and 20 μm in diameter. The chromosomal strands are formed after repeated division of the chromosome in the absence of cytoplasmic division. This type of division is called endomitosis. The polytene chromosome contains two types of bands, dark bands and interbands. The dark bands are darkly stained and the inter bands are lightly stained with nuclear stains. The dark bands contain more DNA and less RNA. The interbands contain more RNA and less DNA. The amount of DNA in interbands ranges from 0.8 - 25%. [2]

The bands of polytene chromosomes become enlarged at certain times to form swellings called puffs. The formation of puffs is called puffing. In the regions of puffs, the chromonemata uncoil and open out to form many loops. The puffing is caused by the uncoiling of individual chromomeres in a band. The puffs indicate the site of active genes where mRNA synthesis takes place. [7] The chromonemata of puffs give out a series of many loops laterally. As these loops appear as rings, they are called Balbiani rings after the name of the researcher who discovered them. They are formed of DNA, RNA and a few proteins. As they are the site of transcription, transcription mechanisms such as RNA polymerase and ribonucleoproteins are present.

In protozoans, there is no transcription, since the puff consists only of DNA. [2]

History

Polytene chromosomes were originally observed in the larval salivary glands of Chironomus midges by Édouard-Gérard Balbiani in 1881. [8] Balbiani described the chromosomal puffs among the tangled thread inside the nucleus, and named it "permanent spireme". In 1890, he observed similar spireme in a ciliated protozoan Loxophyllum meleagris. [1] The existence of such spireme in Drosophila melanogaster was reported by Bulgarian geneticist Dontcho Kostoff in 1930. Kostoff predicted that the discs (bands) which he observed were "the actual packets in which inherited characters are passed from generation to generation." [9]

The hereditary nature of these structures was not confirmed until they were studied in Drosophila melanogaster in the early 1930s by German biologists Emil Heitz and Hans Bauer. In 1930, Heitz studied different species of Drosophila (D. melanogaster, D. simulans , D. hydei, and D. virilis) and found that all their interphase chromatins in certain cells were swollen and messy. In 1932, he collaborated with Karl Heinrich Bauer with whom he discovered that the tangled chromosomes having distinct bands are unique to the cells of the salivary glands, midgut, Malphigian tubules, and brain of the flies Bibio hurtulunus and Drosophila funebris. The two papers were published in the early 1933. [10] Unaware of these papers, an American geneticist Theophilus Shickel Painter reported in December 1933 the existence of giant chromosome in D. melanogaster (followed by a series of papers the following year). [11] [12] Learning of this, Heitz accused Painter of deliberately ignoring their original publication to claim priority of discovery. [13] In 1935, Hermann J. Muller and A.A. Prokofyeva established that the individual band or part of a band corresponds with a gene in Drosophila. [14] The same year, P.C. Koller hesitantly introduced the name "polytene" to describe the giant chromosome, writing:

It seems that we can regard these chromosomes as corresponding with paired pachytene chromosomes at meiosis in which the intercalary parts between chromomeres have been stretched and separated into smaller units, and in which, instead of two threads lying side by side, we have 16 or even more. Hence they are "polytene" rather than pachytene; I do not, however, propose to use this term; I shall refer to them as "multiple threads." [15]

Occurrence

Polytene chromosomes are present in secretory tissues of dipteran insects such as the Malpighian tubules of Sciara and also in protists, plants, mammals, or in cells from other insects. Some of the largest polytene chromosomes described thus far occur in larval salivary gland cells of the chironomid genus Axarus .

In plants, they are found in only a few species, and are restricted to ovary and immature seed tissues such as in Phaseolus coccineus and P. vulgaris (Nagl, 1981), and the anther tapetum of Vigna unguiculata and of some Phaseolus species. [16]

Polytene chromosomes are also used to identify the species of chironomid larvae that are notoriously difficult to identify. Each morphologically distinct group of larvae consists of a number of morphologically identical (sibling) species that can only be identified by rearing adult males or by cytogenetic analysis of the polytene chromosomes of the larvae. Karyotypes are used to confirm the presence of specific species and to study genetic diversity in species with a wide range of genetic variation. [17] [18]

Related Research Articles

<i>Drosophila</i> Genus of flies

Drosophila is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies ; tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly.

<span class="mw-page-title-main">Transposable element</span> Semiparasitic DNA sequence

A transposable element is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transposition often results in duplication of the same genetic material. In the human genome, L1 and Alu elements are two examples. Barbara McClintock's discovery of them earned her a Nobel Prize in 1983. Its importance in personalized medicine is becoming increasingly relevant, as well as gaining more attention in data analytics given the difficulty of analysis in very high dimensional spaces.

<span class="mw-page-title-main">Genetic recombination</span> Production of offspring with combinations of traits that differ from those found in either parent

Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) interchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes ; & (2) intrachromosomal recombination, occurring through crossing over.

<span class="mw-page-title-main">Calvin Bridges</span> American scientist (1889–1938)

Calvin Blackman Bridges was an American scientist known for his contributions to the field of genetics. Along with Alfred Sturtevant and H.J. Muller, Bridges was part of Thomas Hunt Morgan's famous "Fly Room" at Columbia University.

<i>Drosophila melanogaster</i> Species of fruit fly

Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly", or "banana fly". Starting with Charles W. Woodworth's 1901 proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in genetics, physiology, microbial pathogenesis, and life history evolution. As of 2017, six Nobel Prizes have been awarded to drosophilists for their work using the insect.

<span class="mw-page-title-main">Ecdysone</span> Chemical compound

Ecdysone is a prohormone of the major insect molting hormone 20-hydroxyecdysone, secreted from the prothoracic glands. It is of steroidal structure. Insect molting hormones are generally called ecdysteroids. Ecdysteroids act as moulting hormones of arthropods but also occur in other related phyla where they can play different roles. In Drosophila melanogaster, an increase in ecdysone concentration induces the expression of genes coding for proteins that the larva requires. It causes chromosome puffs to form in polytene chromosomes. Recent findings in the laboratory of Chris Q. Doe have found a novel role of this hormone in regulating temporal gene transitions within neural stem cells of the fruit fly.

<i>Drosophila</i> embryogenesis Embryogenesis of the fruit fly Drosophila, a popular model system

Drosophila embryogenesis, the process by which Drosophila embryos form, is a favorite model system for genetics and developmental biology. The study of its embryogenesis unlocked the century-long puzzle of how development was controlled, creating the field of evolutionary developmental biology. The small size, short generation time, and large brood size make it ideal for genetic studies. Transparent embryos facilitate developmental studies. Drosophila melanogaster was introduced into the field of genetic experiments by Thomas Hunt Morgan in 1909.

<span class="mw-page-title-main">Michael Ashburner</span> English biologist (1942–2023)

Michael Ashburner was an English biologist and Professor in the Department of Genetics at University of Cambridge. He was also the former joint-head and co-founder of the European Bioinformatics Institute (EBI) of the European Molecular Biology Laboratory (EMBL) and a Fellow of Churchill College, Cambridge.

Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment, and Hox genes in vertebrates specify the types and shape of vertebrae that will form. In segmented animals, Hox proteins thus confer segmental or positional identity, but do not form the actual segments themselves.

<span class="mw-page-title-main">Chromomere</span>

A chromomere, also known as an idiomere, is one of the serially aligned beads or granules of a eukaryotic chromosome, resulting from local coiling of a continuous DNA thread. Chromomeres are regions of chromatin that have been compacted through localized contraction. In areas of chromatin with the absence of transcription, condensing of DNA and protein complexes will result in the formation of chromomeres. It is visible on a chromosome during the prophase of meiosis and mitosis. Giant banded (Polytene) chromosomes resulting from the replication of the chromosomes and the synapsis of homologs without cell division is a process called endomitosis. These chromosomes consist of more than 1000 copies of the same chromatid that are aligned and produce alternating dark and light bands when stained. The dark bands are the chromomere.

<i>Rhynchosciara americana</i> Species of fly

Rhynchosciara americana is a species of fly. It has a life cycle of approximately 70 days, and the sibling larvae show a synchronized development. The larvae can reach one inch in length, and the adult fly is about 0.8 inch (20 mm). The larvae groups are usually originated from the same female posture and spin a communal cocoon where the metamorphosis will occur. The fly is scientifically notable for the physiology of its polytene chromosomes and developmentally regulated amplified puffs, first observed by Crodowaldo Pavan.

<i>doublesex</i> Gene of insects

Doublesex (dsx) is a gene that is involved in the sex determination system of many insects including the fruit fly Drosophila melanogaster.

<span class="mw-page-title-main">Hsromega</span> Gene found in Drosophila

The developmentally active and heat shock inducible hsromega or hsrω gene in Drosophila produces multiple long non-coding RNA transcripts. This gene is transcriptionally active in almost all cell types of Drosophila and is the most actively induced following heat shock. A unique feature of the hsromega gene, which led to discovery of the 93D puff in 1970, is its singular inducibility with benzamide and a variety of other amides.

<span class="mw-page-title-main">Sarah Elgin</span> American biologist

Sarah C.R. Elgin is an American biochemist and geneticist. She is the Viktor Hamburger Professor of biology at Washington University in St. Louis, and is noted for her work in epigenetics, gene regulation, and heterochromatin, and for her contributions to science education.

<i>Drosophila hydei</i> Species of fly

Drosophila hydei (mosca casera) is a species of Diptera, or the order of flies, in the family Drosophilidae. It is a species in the hydei species subgroup, a group in the repleta species group. Bizarrely, it is also known for having approximately 23 mm long sperm, 10 times the length of the male's body. Drosophila hydei are commonly found on compost piles worldwide, and can be rudimentarily identified by eye owing to their large size and variegated pigment pattern on the thorax. The name derives from Dr R. R. Hyde, who first discovered that the species was distinct from Drosophila repleta. D. hydei are one of the more popular flies used as feeders in the pet trade. A few varieties are available, some flightless. They are very similar to Drosophila melanogaster, despite having separated 50 million years ago.

<i>Cycle</i> (gene)

Cycle (cyc) is a gene in Drosophila melanogaster that encodes the CYCLE protein (CYC). The Cycle gene (cyc) is expressed in a variety of cell types in a circadian manner. It is involved in controlling both the sleep-wake cycle and circadian regulation of gene expression by promoting transcription in a negative feedback mechanism. The cyc gene is located on the left arm of chromosome 3 and codes for a transcription factor containing a basic helix-loop-helix (bHLH) domain and a PAS domain. The 2.17 kb cyc gene is divided into 5 coding exons totaling 1,625 base pairs which code for 413 aminos acid residues. Currently 19 alleles are known for cyc. Orthologs performing the same function in other species include ARNTL and ARNTL2.

Vrille (vri) is a bZIP transcription factor found on chromosome 2 in Drosophila melanogaster. Vrille mRNA and protein product (VRI) oscillate predictably on a 24-hour timescale and interact with other circadian clock genes to regulate circadian rhythms in Drosophila. It is also a regulator in embryogenesis; it is expressed in multiple cell types during multiple stages in development, coordinating embryonic dorsal/ventral polarity, wing-vein differentiation, and ensuring tracheal integrity. It is also active in the embryonic gut but the precise function there is unknown. Mutations in vri alter circadian period and cause circadian arrhythmicity and developmental defects in Drosophila.

<i>De novo</i> gene birth Evolution of novel genes from non-genic DNA sequence

De novo gene birth is the process by which new genes evolve from DNA sequences that were ancestrally non-genic. De novo genes represent a subset of novel genes, and may be protein-coding or instead act as RNA genes. The processes that govern de novo gene birth are not well understood, although several models exist that describe possible mechanisms by which de novo gene birth may occur.

<span class="mw-page-title-main">Sarcophaga barbata</span> Fly species

Sarcophaga barbata is a species from the genus Sarcophaga and the family of flesh fly, Sarcophagidae. It is most closely related to S. plinthopyga, S. securifera, and S. bullata of the same genus. The species was first discovered by Eugene Thomson in 1868. S. barbata has also been found in the Middle East near carcasses, where the larvae can thrive. S. barbata is also a prominent organism in scientific research and has been used to study L-3-glycerophosphate oxidation and location within the mitochondria.

Ferruccio Ritossa was an Italian geneticist best known for his discovery of the heat shock response in the model organism Drosophila.

References

  1. 1 2 Zhimulev, Igor F; Koryakov, Dmitry E (2009). "Polytene Chromosomes". eLS. Chichester (UK): John Wiley & Sons, Inc. pp. 1–10. doi:10.1002/9780470015902.a0001183.pub2. ISBN   978-0-470-01617-6.
  2. 1 2 3 Sumner, Adrian T. (2002). Chromosomes Organization and Function. Chichester: John Wiley & Sons. pp. 182–193. ISBN   978-0-470-69522-7.
  3. ↑ Alanen, M. (1986). "Whole mount electron microscopic maps of Drosophila melanogaster polytene chromosomes". Hereditas. 104 (1): 91–101. doi: 10.1111/j.1601-5223.1986.tb00521.x .
  4. ↑ Hartwell, Leland; Leroy Hood; Michael L. Goldberg; Ann E. Reynolds; Lee M. Silver (2011). Genetics:From Genes to Genomes; Fourth Edition. New York, NY: McGraw-Hill. ISBN   978-0-07-352526-6.
  5. ↑ Zykova, Tatyana Yu; Levitsky, Victor G.; Belyaeva, Elena S.; Zhimulev, Igor F. (April 2018). "Polytene Chromosomes – A Portrait of Functional Organization of the Drosophila Genome". Current Genomics. 19 (3): 179–191. doi:10.2174/1389202918666171016123830. ISSN   1389-2029. PMC   5850506 . PMID   29606905.
  6. ↑ Zhimulev, Igor F.; Belyaeva, Elena S.; Vatolina, Tatiana Yu; Demakov, Sergey A. (2012). "Banding patterns in Drosophila melanogaster polytene chromosomes correlate with DNA-binding protein occupancy". BioEssays. 34 (6): 498–508. doi:10.1002/bies.201100142. PMID   22419120. S2CID   32071983.
  7. ↑ Zhimulev, IF; Belyaeva, ES; Semeshin, VF; Koryakov, DE; Demakov, SA; Demakova, OV; Pokholkova, GV; Andreyeva, EN (2004). Polytene Chromosomes: 70 Years of Genetic Research. International Review of Cytology. Vol. 241. pp. 203–275. doi:10.1016/S0074-7696(04)41004-3. ISBN   978-0-12-364645-3. PMID   15548421.
  8. ↑ Balbiani EG (1881). "Sur la structure du noyau des cellules salivaires chez les larves de Chironomus". Zool. Anz. 4: 637–641.
  9. ↑ Kostoff, Dontcho (1930). "Discoid Structure of the Spireme". Journal of Heredity. 21 (7): 323–324. doi:10.1093/oxfordjournals.jhered.a103356.
  10. ↑ D'Angelo, E.G. (1946). "Micrurgical studies on Chironomus salivary gland chromosomes". The Biological Bulletin. 90 (1): 71–87. doi:10.2307/1538062. JSTOR   1538062. PMID   21014277.
  11. ↑ Falk, R. (2004). "Applying and extending the notion of genetic linkage: the first fifty years". In Gaudillière, Jean-Paul; Rheinberger, Hans-Jörg (eds.). Classical Genetic Research and Its Legacy: The Mapping Cultures of Twentieth-Century Genetics. Oxon: Routledge. p. 52. ISBN   978-0-203-37529-7.
  12. ↑ Painter, T. S. (1933-12-22). "A New Method for the Study of Chromosome Rearrangements and the Plotting of Chromosome Maps". Science. 78 (2034): 585–586. Bibcode:1933Sci....78..585P. doi:10.1126/science.78.2034.585. ISSN   0036-8075. PMID   17801695.
  13. ↑ Zacharias, H (1995). "Emil Heitz (1892-1965): chloroplasts, heterochromatin, and polytene chromosomes". Genetics. 141 (1): 7–14. doi:10.1093/genetics/141.1.7. PMC   1206741 . PMID   8536991.
  14. ↑ Muller, HJ; Prokofyeva, AA (1935). "The Individual Gene in Relation to the Chromomere and the Chromosome". Proceedings of the National Academy of Sciences of the United States of America. 21 (1): 16–26. Bibcode:1935PNAS...21...16M. doi: 10.1073/pnas.21.1.16 . PMC   1076520 . PMID   16577650.
  15. ↑ Koller, P. C. (1935). "The Internal Mechanics of the Chromosomes. IV.—Pairing and Coiling in Salivary Gland Nuclei of Drosophila". Proceedings of the Royal Society B: Biological Sciences. 118 (810): 371–397. Bibcode:1935RSPSB.118..371K. doi: 10.1098/rspb.1935.0062 .
  16. ↑ Carvalheira, Gianna Maria Griz (2000). "Plant polytene chromosomes". Genetics and Molecular Biology. 23 (4): 1043–1050. doi: 10.1590/S1415-47572000000400050 .
  17. ↑ Int Panis L, Kiknadze I, Bervoets L, Aimanova A (1994). "Karyological identification of some species of the genus Chironomus Meigen, 1803 from Belgium". Bull. Ann. Soc. R. Ent. Belg. 130: 135–142.
  18. ↑ Кикнадзе ИИ; Михайлова П; Истомина АГ; Голыгина ВВ; Инт Панис Л; Крастанов Б (2006). "Хромосомный полиморфизм и дивергенция популяций у Chironomus nuditarsis Keyl (Diptera, Chironomidae)". Tsitologia. 48: 595–609.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.