Co-localization of ribosomal and telomeric sequences in Leptynia (Insecta: Phasmatodea)

Abstract

Stick insects have been studied mainly for non-conventional reproduction modes, such as parthenogenesis, hybridogenesis and androgenesis. Parallel karyological investigations have evidenced extensive numerical and structural chromosome re-patterning, particularly evident in hybrid parthenogenetic taxa. Chromosome sets of bisexual Leptynia (Pantel) species show an evolutionary trend from 40 to 36 chromosomes and are characterized by cytological satellites of variable size and localization. We performed fluorescence in situ hybridization (FISH) analysis using 45S ribosomal genes and pentameric (TTAGG)n telomere sequences as probes in two strictly related but karyotypically distinct species, L. montana Scali (2n = 38/37; XX/XO) and L. attenuata Pantel (2n = 36). L. attenuata has recently been split into three subspecies (L. attenuata attenuata, L. attenuata iberica and L. attenuata algarvica), and found to share an XX/XY sex chromosome formula, unusual for stick insects. FISH by 45S rDNA sequences consistently labelled the short arm of the 4th chromosome pair, often of a variable size. Silver staining showed that nucleolar organizer regions (NORs) are active. FISH of the telomeric repeats, besides ordinary telomeres, also labelled the short arm of this same pair. The use of both probes in double FISH analysis fully confirmed the co-localization of ribosomal and telomeric highly repeated sequences. Since it is increasingly emerging that the co-localization of NORs and telomeric sequences appears to be a feature shared by evolutionarily distant animals, its possible role is discussed.

Telomere structure in insects: A review

“…So far, telomeres of 11 species from seven genera of the only family Phasmatidae were studied. All of them were shown to be positive for the (TTAGG) n telomere motif (Frydrychová et al, ; Liehr et al, ; Scali et al, ). In some species, e.g., the Annam walking stick, Medauroidea extradentata Brunner von Wattenwyl, 1907, as well as Leptynia montana Scali, 1996 and L. attenuata Pantel, 1890, ITSs were present on certain chromosomes, in addition to telomeres (Liehr et al, ; Scali et al, ).…”

“…All of them were shown to be positive for the (TTAGG) n telomere motif (Frydrychová et al, ; Liehr et al, ; Scali et al, ). In some species, e.g., the Annam walking stick, Medauroidea extradentata Brunner von Wattenwyl, 1907, as well as Leptynia montana Scali, 1996 and L. attenuata Pantel, 1890, ITSs were present on certain chromosomes, in addition to telomeres (Liehr et al, ; Scali et al, ). On the contrary, no pericentromeric ITSs were detected on the neo‐X chromosome of L. attenuata , suggesting that they were either inactivated or eliminated from the fused chromosome (Scali et al, ).…”

“…Since this compilation, the number of species and higher taxa targeted by telomere studies experienced a manifold increase. New data became available for many previously poorly studied or unexplored orders such as Odonata (Kuznetsova et al, ), Orthoptera (Buleu, Jetybayev, Chobanov, & Bugrov, ; Kociński, Grzywacz, Chobanov, & Warchałowska‐Śliwa, ), Phasmatodea (Liehr, Buleu, Karamysheva, Bugrov, & Rubtsov, ; Scali et al, ), Mantophasmatodea (Lachowska‐Cierlik, Maryańska‐Nadachowska, Kuznetsova, & Picker, ), Hemiptera (Anjos, Rocha, Paladini, Mariguela, & Cabral‐de‐Mello, ; Chirino et al, ; Grozeva, Kuznetsova, & Anokhin, ; Kuznetsova, Grozeva, Hartung, & Anokhin, ; Luan, Sun, Fei, & Douglas, ; Mandrioli, Zanasi, & Manicardi, ; Maryańska‐Nadachowska, Kuznetsova, Golub, & Anokhin, ; Mohan, Rani, Kulashreshta, & Kadandale, ), Neuroptera (Kuznetsova, Khabiev, & Anokhin, ), Coleoptera (Mravinac et al, ), Hymenoptera (Gokhman et al, ; Gokhman & Kuznetsova, ; Menezes et al, ) and others (see Figure , Appendix ). All this information was mainly obtained by FISH and is therefore more reliable if compared with SBH, because, when (TTAGG) n sequences are detected by the latter technique, they are not necessarily telomeric, as the specific probe could also hybridize with repetitive sequences located at non‐telomeric sites (Meyne et al, ; Sahara et al, ).…”

New Insights into Phasmatodea Chromosomes

“…Another peculiar karyotypic feature of stick insects relates to the presence/absence and different numbers and sizes of cytological visible satellites, varying among co-generic and even within the same species [ 16 , 17 , 18 , 19 , 20 ]. For two species from the genus Leptynia , Leptynia montana (2n = 38/37; XX/X0) [ 21 ], L. attenuate (2n = 36/36; XX/XY) (subspecies L. attenuata attenuate , L. attenuata iberica , L. attenuata algarvica ) regions enriched for 45S ribosomal deoxyribonucleic acid (rDNA) and telomeric repeats (TTAGG) n were reported [ 22 ].…”

“…Even centromere banding staining (C-banding) of stick insect chromosomes was described only for a few species [ 23 , 24 ]. Molecular cytogenetics, i.e., fluorescence in situ hybridization (FISH) in stick insects, was applied in a single study [ 22 ]. Thus, here we intended to provide karyotypic characterization of the following five species from four families applying C-banding, and to characterize the distribution of 18S rDNA and telomeric repeats by FISH:…”