Karyotype evolution in the horseshoe bat Rhinolophus sedulus by whole-arm reciprocal translocation (WART)

Robertsonian (centric) fusion or fission is one of the predominant modes of chromosomal rearrangement in karyotype evolution among mammals. However, in karyotypes composed of only bi-armed chromosomes, creation of new chromosomal arm combinations in one step is possible only via whole-arm reciprocal translocation (WART). Although this type of rearrangement has often been proposed to play an important role in chromosomal evolution, direct observations of WARTs remained rare, and, in most cases, were found in hybrids of chromosomal races in the genera Mus and Sorex. For the first time, we present the karyotype of the horseshoe bat species Rhinolophus sedulus (2n = 28, FNa = 52), where a WART between 2 metacentric autosomes was detected by G-banding and confirmed by FISH with painting probes of the vespertilionid bat Myotis myotis. Among the 6 specimens analyzed, 2 showed the heterozygous condition of the WART, 1 showed the presumed ancestral, and 3 specimens showed the derived homozygous state. As the existence of a hybrid zone at the sampling locality is thought to be rather improbable, the WART may indicate ongoing karyotype evolution in this taxon

Early Embryonic Chromosome Instability Results in Stable Mosaic Pattern in Human Tissues

The discovery of copy number variations (CNV) in the human genome opened new perspectives on the study of the genetic causes of inherited disorders and the aetiology of common diseases. Here, a single-cell-level investigation of CNV in different human tissues led us to uncover the phenomenon of mitotically derived genomic mosaicism, which is stable in different cell types of one individual. The CNV mosaic ratios were different between the 10 individuals studied. However, they were stable in the T lymphocytes, immortalized B lymphoblastoid cells, and skin fibroblasts analyzed in each individual. Because these cell types have a common origin in the connective tissues, we suggest that mitotic changes in CNV regions may happen early during embryonic development and occur only once, after which the stable mosaic ratio is maintained throughout the differentiated tissues. This concept is further supported by a unique study of immortalized B lymphoblastoid cell lines obtained with 20 year difference from two subjects. We provide the first evidence of somatic mosaicism for CNV, with stable variation ratios in different cell types of one individual leading to the hypothesis of early embryonic chromosome instability resulting in stable mosaic pattern in human tissues. This concept has the potential to open new perspectives in personalized genetic diagnostics and can explain genetic phenomena like diminished penetrance in autosomal dominant diseases. We propose that further genomic studies should focus on the single-cell level, to better understand the aetiology of aging and diseases mediated by somatic mutations

The Human Genome Puzzle – the Role of Copy Number Variation in Somatic Mosaicism

The discovery of copy number variations (CNV) in the human genome opened new perspectives in the study of the genetic causes of inherited disorders and the etiology of common diseases. Differently patterned instances of somatic mosaicism in CNV regions have been shown to be present in monozygotic twins and throughout different tissues within an individual. A single-cell-level investigation of CNV in different human cell types led us to uncover mitotically derived genomic mosaicism, which is stable in different cell types of one individual. A unique study of immortalized B-lymphoblastoid cell lines obtained with 20 year interval from the same two subjects shows that mitotic changes in CNV regions may happen early during embryonic development and seem to occur only once, as levels of mosaicism remained stable. This finding has the potential to change our concept of dynamic human genome variation. We propose that further genomic studies should focus on the single-cell level, to understand better the etiology and physiology of aging and diseases mediated by somatic variations

Variations on a theme: Karyotype comparison in Eurasian Myotis species and implications for phylogeny

Abstract. The phylogenetic relationships within the large genus Myotis are still unsolved to a high degree although several morphological and molecular studies have been undertaken recently. In cytogenetic respect, Myotis is a very homogeneous genus as nearly all species show a karyotype with 44 chromosomes. Application of banding techniques in 17 Eurasian Myotis taxa revealed complete conservation of chromosomes. However, variation has been found concerning position and extent of heterochromatic segments and location and number of nucleolus organizer regions (NORs). In three cases these differences may be of relevance for phylogenetic relationships. The close affinity of M. myotis, M. blythii and M. nattereri shown in molecular studies was confirmed by a common interstitial heterochromatic segment on chromosome 15 in these species. The presence of two cryptic species in M. montivagus, suspected earlier for the reason of a 5% difference in mtDNA sequences, was fortified by the observation of a distinct karyological difference, i.e. a pericentric inversion on chromosome 7. In contrast to previous molecular studies, Greek specimens of M. mystacinus were clearly differentiated from German specimens concerning the location of NORs and size and morphology of the Y chromosome. The Greek specimens were provisionally assigned to the subspecies M. mystacinus bulgaricus

Chromosomal Evolution in Chiroptera

Chiroptera is the second largest order among mammals, with over 1300 species in 21 extant families. The group is extremely diverse in several aspects of its natural history, including dietary strategies, ecology, behavior and morphology. Bat genomes show ample chromosome diversity (from 2n = 14 to 62). As with other mammalian orders, Chiroptera is characterized by clades with low, moderate and extreme chromosomal change. In this article, we will discuss trends of karyotypic evolution within distinct bat lineages (especially Phyllostomidae, Hipposideridae and Rhinolophidae), focusing on two perspectives: evolution of genome architecture, modes of chromosomal evolution, and the use of chromosome data to resolve taxonomic problems

Wing membrane biopsies for bat cytogenetics: Finding of 2n = 54 in irish Rhinolophus hipposideros (rhinolophidae, chiroptera, mammalia) supports two geographically separated chromosomal variants in Europe

In Europe, 2 different diploid chromosome numbers, 2n = 54 and 2n = 56, have been described in the lesser horseshoe bat (Rhinolophushipposideros). The eastern form with 2n = 56 extends from the Czech Republic to Greece. To date, specimens with 54 chromosomes have been reported only from Spain and Germany. This study expands the distributional area of the western variant to Ireland. Strikingly, this distribution of European chromosomal variants is in contrast to the available molecular data that indicate little genetic differentiation of R. hipposideros populations spanning Northwestern to Central Europe. Further, we have developed an optimized protocol for establishing fibroblast cell cultures, suitable for karyotype analyses, from 3-mm wing membrane biopsies. This is a useful technique for cytogenetic studies of endangered bat species, as this non-lethal sampling method imposes only minimum stress to the animal without lasting adverse effects and is routinely used to sample tissue probes for molecular genetic studies in bats.European Research CouncilUniversity College Dubli

Karyotype comparison of five African Vespertilionini species with comments on phylogenetic relationships and proposal of a new subtribe

Volleth, Marianne, Mayer, Frieder, Heller, Klaus-Gerhard, Müller, Stefan, Fahr, Jakob (2023): Karyotype comparison of five African Vespertilionini species with comments on phylogenetic relationships and proposal of a new subtribe. Acta Chiropterologica 25 (1): 35-52, DOI: 10.3161/15081109ACC2023.25.1.00

Nycticeinops schlieffenii

<i>Nycticeinops schlieffenii</i> (Peters, 1859) <p> The karyotype of <i>N. schlieffenii</i> consisted of nine meta- to submetacentric and seven acrocentric autosomal pairs (2n = 34 and FNa = 50). The X chromosomes were medium-sized metacentrics with a G-banding pattern characteristic for vespertilionid state II. In addition to the ancestral four bi-armed pairs, 1/2, 3/4, 5/6 and 16/17, derived Robertsonian fusion chromosomes 7/11, 8/12, 9/13, 10/14 and 21/22 were observed (Fig. 11).</p> <p>The SC close to the centromere of the acro-centric chromosome 15 was confirmed by AgNOR staining as nucleolus organizer region. The mean number of active NORs per cell was 1.9 (16 cell scored). Apart from the centromeres, C-positive heterochromatin was present in the proximal part of one of the two smallest acrocentric pairs, homologous to MMY24 or MMY25 (Fig. 6C). The chromosomes 1/2, 11, 12, and 15 were present in vespertilionid state II.</p>Published as part of <i>Volleth, Marianne, Mayer, Frieder, Heller, Klaus-Gerhard, Müller, Stefan & Fahr, Jakob, 2023, Karyotype comparison of five African Vespertilionini species with comments on phylogenetic relationships and proposal of a new subtribe, pp. 35-52 in Acta Chiropterologica 25 (1)</i> on page 44, DOI: 10.3161/15081109ACC2023.25.1.00

Pseudoromicia brunnea

<i>Pseudoromicia brunnea</i> (Thomas, 1880) <p> The karyotype of this species consisted of 2n = 36 chromosomes with FNa = 50 (Fig. 4), including seven large to medium meta- to submetacentric, one small submetacentric, and nine small acrocentric autosomal pairs. The X chromosome was a medium-sized submetacentric and the Y chromosome a small bi-armed chromosome. The bi-armed autosomal elements showed the following combination of chromosomal arms: 1/2, 3/4, 5/6 and 16/17 as in the vespertilionid basic karyotype, as well as derived associations 7/11, 8/9, 10/12, and 14/18. Two autosomal pairs showed derived conditions due to intrachromosomal rearrangements. The bi-armed element 3/4, which is metacentric in the basic karyotype, was submetacentric in <i>P. brunnea</i>. The formerly proximal part of arm 3, bearing homologous sequences to <i>Eulemur</i> chromosome EMA8, was shown to be situated in the proximal part of the long arm of <i>P. brunnea</i> chromosome 3/4 (Fig. 5). This rearranged chromosome resulted either from a centromere repositioning or a pericentric inversion. Another presumed centromere repositioning in the formerly metacentric element 16/17 resulted in a submetacentric chromosome with a slightly enlarged arm 17.</p> <p> The single NOR was found at the SC close to the centromere of arm 15. The mean number of active NORs per cell was 1.95 (20 cell scored from the male specimen). C-banding revealed only weak centromeric staining on the bi-armed elements but clear C-bands at the centromeres of the acrocentric elements, especially pronounced on chromosome 24. <i>P. brunnea</i> chromosome 5/6 showed a large heterochromatin block in arm 5 close to the centromere, resulting in a clearly enlarged size of arm 5 (Fig. 6A). A small intercalary heterochromatic band was found in the rearranged chromosome 3/4 on the long arm, approximately at the former location of the centromere. The small bi-armed Y chromosome consisted largely of C-positive heterochromatic material.</p> <p> The G-banding pattern of the submetacentric X chromosome differed from that of state II in the basic karyotype. In <i>P. brunnea</i>, presumably due to a small pericentric inversion or centromere repositioning, the short arm and the proximal part of the long arm of the ancestral X, state II, constituted the long arm, whereas the distal part of the formerly long arm now built up the short arm (Fig. 7).</p> <p> The chromosomes 1/2, 11, 12, and 15 were present in state II. Therefore, <i>P. brunnea</i> is clearly a member of the tribe Vespertilionini sensu Volleth and Heller (1994).</p>Published as part of <i>Volleth, Marianne, Mayer, Frieder, Heller, Klaus-Gerhard, Müller, Stefan & Fahr, Jakob, 2023, Karyotype comparison of five African Vespertilionini species with comments on phylogenetic relationships and proposal of a new subtribe, pp. 35-52 in Acta Chiropterologica 25 (1)</i> on pages 41-42, DOI: 10.3161/15081109ACC2023.25.1.00

Laephotis kirinyaga Monadjem, Patterson, Webala and Demos 2021

Laephotis kirinyaga <i>Monadjem, Patterson, Webala and Demos, 2021</i> <p> The diploid chromosome number of the male studied was 2n = 32, the fundamental number of autosomal arms was FNa = 50. The karyotype comprised nine large- to medium-sized meta- to submetacentric, one small metacentric and five small acrocentric autosomal pairs (Fig. 1). Four metacentric pairs similar to that of the vespertilionid basic karyotype (2n = 44, numbering of chromosomal arms as in the genus <i>Myotis</i>) were present. Further, Robertsonian fusion products were identified according to the G-banding pattern with the following arm combinations: 7/11, 8/9, 10/12, 13/18, 14/20 and 15/21. Chromosomes 19 and 22 to 25 were acrocentric elements. The X chromosome was a medium-sized metacentric chromosome with the banding pattern characteristic for Vespertilionini and Pipistrellini (state II — Volleth and Heller, 1994). The Y chromosome was about of the same size as chromosome 23 and consisted largely of heterochromatic material. Chromosomes 1/2, 11, 12 and 15 were present in state II as in other members of the tribe Vespertilionini. The nucleolus organizing regions (NORs) were located at the secondary constriction (SC) of arm 15. C-band positive heterochromatin was present only at the centromeres and the Y chromosome.</p>Published as part of <i>Volleth, Marianne, Mayer, Frieder, Heller, Klaus-Gerhard, Müller, Stefan & Fahr, Jakob, 2023, Karyotype comparison of five African Vespertilionini species with comments on phylogenetic relationships and proposal of a new subtribe, pp. 35-52 in Acta Chiropterologica 25 (1)</i> on page 39, DOI: 10.3161/15081109ACC2023.25.1.002, <a href="http://zenodo.org/record/10265140">http://zenodo.org/record/10265140</a&gt