Aquatic silk proteins in Chironomus: A review

Silk proteins secreted by salivary glands in the dipteran insect, Chironomus play a significant role as proteinaceous adhesives for construction of underwater housing nests by larvae. To date, only three Chironomus species, C. tentans Fabricius, C. pallidivittatus Malloch and C. riparius Meigen have been explored for characterization of their aquatic silk protein. Genes coding for silk proteins are located on specific chromosomal ‘puffs’ called Balbiani rings as well as non-Balbiani ring regions. Expression of these genes is closely regulated by developmental and hormonal alterations and environmental factors. Furthermore, pilot studies have postulated that silk proteins probably occur in diverse size classes grouped into large (~1000 kDa), intermediate (100-200 kDa) and small (≤100 kDa). Barring few preliminary reports that date back to the 1990s, the physical and bioproperties of silk from chironomid midges remain largely unknown, leading to paucity of updated information. This review was therefore aimed to compile existing literature database and to highlight the wide possibilities for commercialization of midge larval silk as a novel biopolymer.

Chironomus alchichica sp. n. (Diptera: Chironomidae) from Lake Alchichica, Mexico

Morphological analysis of all developmental stages (except female), mitochondrial DNA sequences from cytochrome c oxidase subunit I (cox1) and cytological analysis of the polytene chromosomes were used to describe a new species of Chironomus found in the littoral and profundal zones of an endorheic, warm-monomictic lake in Mexico. Male imago is distinguished by the shape of superior volsella and by an antennal and bristle ratio lower than two. The pupa is characterized by the spur morphology of abdominal segment VIII. There is also a continuous row of hooklets on abdominal segment II. The larva is distinguished by a combination of antenna, mentum, mandible, and pecten epipharyngis characteristics, and abdominal ventral tubules. Molecular and cytological analysis supported the morphological differences found. The maximum likelihood tree obtained shows that Chironomus alchichica sp. n. clusters together with Chironomus decorus-group sp. 2 Butler et al. (1995) (bootstrap support = 92%), but genetic p-distances within C. alchichica sp. n. (0.004) were lower than the p-distances between other species of the decorus-group (C. decorus-group sp. 2, Chironomus bifurcatus Wülker et al., 2009 and Chironomus maturus Johannsen, 1908) confirming that it is a different species. The new species belongs to thummi cytocomplex, (decorus-group), with chromosome set- 2n = 8 and chromosome arm combinations: AB CD EF G. Karyologically, the species is closest to Chironomus riihimaekiensis Wülker (1973). This species has very compact salivary gland chromosomes with well heterochromatinized centromere regions in chromosomes AB CD G. Several fixed homozygous inversions distinguish arm A of the species from that of C. riihimaekiensis. Arm E differs from that of C. riihimaekiensis by simple fixed homozygous inversion. Some similarities in band sequences of this arm were found with species from the decorus-group as Chironomus blaylocki Wülker et al., 2009 and C. bifurcatus (decorus-group). The position of the key constrictions in chromosome G: Nucleolar organizer (NOR) and Balbiani rings (BRs) is similar to the species of decorus-group. C. alchichica sp. n. has been found in soft sediments rich in organic matter in well mineralized waters (where conductivity >10 mS cm-1) and with a high pH (≥9). The profundal zone is inhabited only during the mixing period, when dissolved oxygen is present.

The effect of long-term contamination by heavy metals on community and genome alterations of Chironomidae (Diptera) in a stream with mine drainage water (southern Poland)

This paper reports on studies of the effect of heavy metals on the Chironomidae that inhabit the Matylda stream, which has been contaminated for about 100 years by discharge water from a zinc and lead ore mine. Stream sediment was strongly polluted by Cd, Pb, Cu and Zn. These metals did not affect the Chironomidae community but strongly changed the genome system of the Chironomidae species that inhabited the sediment. The salivary gland chromosomes of six species belonging to the two genera Chironomus and Prodiamesa are analyzed. In all species the somatic index is calculated on the basis of somatic chromosome alterations. Chironomus riparius has the highest numbers of somatic alterations and the highest somatic index — 9.67. The smallest chromosome G carries the key structures known as “Balbiani rings”, which play an important role in species development. This chromosome is very sensitive in the genome of the most studied species. The high sensitivity of the C. riparius genome is discussed in light of its DNA organization. The results show a high response of the salivary gland chromosomes to heavy metal pollution, and this makes them a valuable indicator in the assessment of water quality and detection of mutagenic agents in the aquatic environment.

Cytogenetic comparison of chironomid midge Glyptotendipes glaucus (Meigen, 1818) (Diptera, Chironomidae) populations from Northwest Russia and Ukraine (Chernobyl zone)

Functional characters of polythene chromosomes and chromosomal rearrangements in salivary glands of 177 larvae of Glyptotendipes glaucus (Diptera, Chironomidae) from reservoirs of Russia and Ukraine (Chernobyl) have been analysed. Similarity of the populations studied based on a pool of chromosomal reorganizations has been established. The general types of inversions in chromosomal arms A, B, D and E have been detected. Influence of radioactive pollution (Chernobyl) on functional changes of a nucleus, Balbiani rings, puffs, morphology of disks and interdisks is revealed.

Chironomus (diptera) polytene chromosomes functional activity under the influence of cholinotropic preparations

Morphometric analysis of nucleolar organizer (NO), Balbiani rings (BR) - BR_B, BR_1G, BR_2G, chromosome I arm puff B, chromosomes compactness activity change under the influence of cholinotropic preparations was carried out. Most sensitive criterion - chromosomes compactness is, most stable under the influence of stress - NO is. Atropine and pilocarpine antagonistic effect on the polytene chromosomes (PC) sites activity pilocarpine manifested itself in functional activity and restoration period duration change: on cholinoblocker effect activity decreased, while on cholinomimetic effect activity increased.

Evaluation of the Sensitivity of the Terminal Deoxynucleotidyl Transferase–Immunogold Technique on Balbani Ring Genes

Recently, we developed the terminal deoxynucleotidyl transferase (TdT)–immunogold technique for in situ detection of DNA molecules. In this study the potential value and the limitations of the method were evaluated using the giant polytene chromosomes from Chironomus tentans salivary glands. Emphasis was put on the Balbiani rings (BRs), specialized chromosomal sites with exceptionally intense synthesis of large mRNA molecules. Immunolabeling was recorded not only over the bands and interbands of the polytene chromosomes but also over the BR structures. In the BRs, gold particles were present over segments of active transcription units, each with a central chromatin axis and a number of growing RNP products attached to the axis. One third of the transversely sectioned transcription units showed labeling in the central parts, i.e., where the unfolded chromatin axis is located, whereas the growing RNP fibers remained unlabeled. The absence of labeling of the RNP fibers is not likely to be due to lack of accessibility, because anti-RNA antibodies readily decorated the RNP fibers. The nuclear sap and cytoplasm displayed no significant label. These results clearly indicate that the TdT–immunogold technique is specific for DNA and detects not only DNA in compacted chromatin but also fully extended DNA. Its ability to efficiently label a single DNA molecule demonstrates the method's very high sensitivity.

Cytotaxonomic differentiation of the Afrotropical Drosophila montium subgroup: D. diplacantha and D. seguyi. The major role of reverse tandem duplications

Aiming to establish phylogenetic relationships among species of the montium subgroup, detailed polytene chromosome maps are given showing intraspecific polymorphism and ecdysone induced larval puffing pattern profiles of two Afrotropical members of this subgroup, Drosophila diplacantha and D. seguyi. Both species exhibit two unique characteristics that define the montium subgroup, namely, a large number of reverse tandem duplications and a progressive darkening of anterior spiracles of the late third instar larvae, which is accompanied by a definite temporal and spatial puffing pattern of the salivary gland chromosomes. In contrast with the well-formed Balbiani ring 1 (BR1) observed in Oriental and Indian montium species, BR1 exhibits a different developmental profile in D. diplacantha, while it is obscured in D. seguyi. Although phyletic comparisons of five species from five different complexes within the subgroup show some conservation in banding and puffing pattern homologies, an analysis to assign map sections by sequential rearrangements remains unresolved at this time. The evolution of the subgroup is discussed in relation with the sharing of reverse tandem duplications, especially those including the montium BRs.Key words: Drosophila montium, polytene chromosomes, Balbiani rings, puffs, duplications, inversions.