Amplified Fragments of an Autosome-Borne Gene Constitute a Significant Component of the W Sex Chromosome of Eremias velox (Reptilia, Lacertidae)

Abstract

Heteromorphic W and Y sex chromosomes often experience gene loss and heterochromatinization, which is frequently viewed as their “degeneration”. However, the evolutionary trajectories of the heterochromosomes are in fact more complex since they may not only lose but also acquire new sequences. Previously, we found that the heterochromatic W chromosome of a lizard Eremias velox (Lacertidae) is decondensed and thus transcriptionally active during the lampbrush stage. To determine possible sources of this transcription, we sequenced DNA from a microdissected W chromosome sample and a total female DNA sample and analyzed the results of reference-based and de novo assembly. We found a new repetitive sequence, consisting of fragments of an autosomal protein-coding gene ATF7IP2, several SINE elements, and sequences of unknown origin. This repetitive element is distributed across the whole length of the W chromosome, except the centromeric region. Since it retained only 3 out of 10 original ATF7IP2 exons, it remains unclear whether it is able to produce a protein product. Subsequent studies are required to test the presence of this element in other species of Lacertidae and possible functionality. Our results provide further evidence for the view of W and Y chromosomes as not just “degraded” copies of Z and X chromosomes but independent genomic segments in which novel genetic elements may arise.

Sequencing of laser captured Z and W chromosomes of the tocantins paradoxical frog (Pseudis tocantins) provides insights on repeatome and chromosomal homology

“…The high number of singletons and low‐N50 values indicate that both assemblies are highly fragmented, which could be due to the low coverage of microdissected chromosomes in the sequencing libraries. The number of singletons and N50 values we found for both assemblies were similar to those reported by other authors who sequenced microdissected chromosomes (examples in Traut et al, 2013; Avila et al, 2015; Keinath et al, 2015; Luo et al, 2020; Lisachov et al, 2021). Regarding the contamination rates, the average percentages of human and bacterial reads in Ps.…”

Heteromorphic ZZ/ZW sex chromosomes sharing gene content with mammalian XX/XY are conserved in Madagascan chameleons of the genus Furcifer

“…We microdissected the Z 1 chromosome of F. pardalis and the Z and W chromosomes of F. oustaleti and sequenced the chromosome material in Illumina platform in order to identify their gene content. This approach was previously successfully applied in other reptiles 29 , 30 . For the microdissection, we used a Zeiss Axiovert S200 inverted microscope (Oberkochen, Germany) equipped with an Eppendorf TransferMan NK2 mechanical micromanipulator (Hamburg, Germany).…”

Heteromorphic ZZ/ZW sex chromosomes sharing gene content with mammalian XX/XY are conserved in Madagascan chameleons of the genus Furcifer

“…oustaleti and sequenced the chromosome material in Illumina platform in order to identify their gene content. This approach was previously successfully applied in other reptiles (Lisachov et al 2021, Zhu et al 2022). For the microdissection, we used a Zeiss Axiovert S200 inverted microscope (Oberkochen, Germany) equipped with an Eppendorf TransferMan NK2 mechanical micromanipulator (Hamburg, Germany).…”