Polytene & Lampbrush

Polytene & Lampbrush chromosome in biology

1. POLYTENE CHROMOSOME & Lampbrush chromosome 1 Presented by: Sepideh saroughi

2. What are Polytene and Lampbrush chromosomes? These are also giant chromosomes but relatively smaller than lampbrush chromosomes, found in the larvae of certain dipterans. Because of their large size showing numerous strands these are named as polytene chromosomes (name suggested by Kollar) or commonly salivary gland chromosomes. 2

3. POLYTENE CHROMOSOME 3

4. Polytene chromosomes are large chromosomes which have thousands of DNA strands. S alivary glands of insects First reported by E.G.Balbiani in 1881 Drosophila, Chironomus , Rhynchosciara In insects salivary glands when the cells are not dividing 4

5. Interphase thick and thin banding patterns map chromosomes identify small chromosome mutations function of genes in transcription 5

6. FUNCTION Increasing the volume of the cells' nuclei Cell expansion Metabolic advantage high level of gene expression for example : Bar phenotype of kidney-shaped eyes P rimary functions : Binding sites for RNA pol II I nitiate replication N ucleosome remodeling of short fragments of DNA 6

7. STRUCTURE S alivary gland chromosomes The large size of the chromosome is due to the presence of many longitudinal strands called chromonemata. 0.5 mm in length and 20 μm in diameter The chromosomal strands in the absence of cytoplasmic division E ndomitosis Two types of bands dark bands darkly : more DNA interbands lightly stained with nuclear stains: more RNA The amount of DNA in interbands ranges from 0.8 - 25%. 7

8. The bands of polytene chromosomes become enlarged at certain times to form swellings puffs : the chromonemata uncoil and open The puffs indicate the site of active genes : mRNA synthesis The chromonemata of puffs give out a series of many loops Balbiani rings Balbiani rings : They are formed of DNA, RNA and a few proteins / transcription site / RNA polymerase / ribonucleoproteins In protozoans, there is no transcription, since the puff consists only of DNA. 8

9. HISTORY O bserved by Édouard -Gérard Balbiani in 1881 In 1890, he observed similar spireme in a ciliated protozoan Loxophyllum meleagris . 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 .“ In 1930, Heitz studied different species of Drosophila and found that all their interphase chromatins in certain cells were swollen and messy. 9

10. In 1932, Karl Heinrich Bauer : bands in salivary glands, midgut , Malphigian tubules, and brain of the flies Bibio hurtulunus and Drosophila funebris . P.C. Koller hesitantly introduced the name "polytene" to describe the giant chromosome they are "polytene" rather than pachytene 10

11. OCCURRENCE In secretory tissues of dipteran insects such as the Malpighian tubules of Sciara , plants, mammals, or in cells from other insects. L argest polytene chromosomes in larval salivary gland cells of the chironomid genus Axarus . In plants ovary and immature seed tissues such as in Phaseolus coccineus and P. vulgaris Used to identify the species of chironomid 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. 11

12. Genes Containing Long Introns Occupy Series of Bands and Interbands In Drosophila melanogaster polytene Chromosomes To analyze it, we used bioinformatic approaches and characterized genome-wide distribution of introns in gene bodies and in different chromatin states, and using fluorescent in situ hybridization we juxtaposed them with the chromosome structures. The mapping of the 15 long genes showed that they could occupy extended sections of polytene chromosomes containing band and interband series, with promoters located in the interband fragments. Introns in polytene chromosomes form independent bands, which can contain either both introns and exons or intron material only. Thus , a novel type of the gene arrangement in polytene chromosomes was discovered. 12

13. Do humans have polytene chromosomes ? Are polytene chromosomes haploid or diploid ? How does a polytene chromosome differ from a typical eukaryotic chromosome ? Do polytene chromosomes show somatic pairing? 13

14. Lampbrush chromosome 14

15. Lampbrush chromosome 15

16. Oocyte development takes place during the meiotic prophase and for the majority of species ends in the metaphase of the first meiotic division D iplotene vertebrates , amphibians and birds The loops are transcriptionally active sites . Lampbrush chromosome (immature eggs) of most animals, except mammals. Intermediate structure In a prolonged diplotene stage very large chromosomal structures LBCs ’ length ranges from 400 to 800 mm up to 30 times larger than their mitotic counterparts. 16

17. STRUCTURE LBC is a bivalent I nactive chromatin / side loops of decondensed chromatin In the homologous sections of the bivalent, chromatin is condensed. The loop constitutes a part of the chromosome axis. It is extensible as well as contractible contraction and dilation of the chromomere 17

18. Lampbrush chromosomes include domains of open chromatin in which the genes can be potentially transcriptive and domains of locked chromatin without expression . Lampbrush chromosome loops are considered an example of open chromatin . Their analogues are thought to be the “ puffs ” of polytenic chromosomes.They differ between each other . Polytenic chromosomes parallel chromatids lampbrush chromosome chromatin single DNA helix 18

19. HISRORY Lampbrush chromosomes were discovered in salamander egg cells by Flemming . Ten years later, LBCs were identified in shark egg cells and described by Rückert in 1892 . It was Rückert who introduced the term “ lampbrush chromosome” into biological nomenclature. The chromosomes obtain their name from the 19th century brushes that were used for cleaning street lamps to which Rückert likened them to the same. 19

20. Visible in the light microscope Each lateral loop contains one or several transcription units with polarized RNP-matrix coating the DNA axis of the loop. U sed for high-resolution mapping of DNA sequences and construction of detail cytological maps of individual chromosomes . Lampbrush chromosomes are also involved in the production of “masked” mRNAs for early development 1. mRNAs are packaged 2. specific alterations of the deoxyribonucleoprotein 20

21. What is the function of Lampbrush chromosome ? Do humans have Lampbrush chromosomes ? Where is Lampbrush chromosome found ? 21

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