Cross-Species BAC Mapping Highlights Conservation of Chromosome Synteny across Dragon Lizards (Squamata: Agamidae)

Abstract

Dragon lizards (Squamata: Agamidae) comprise about 520 species in six subfamilies distributed across Asia, Australasia and Africa. Only five species are known to have sex chromosomes. All of them possess ZZ/ZW sex chromosomes, which are microchromosomes in four species from the subfamily Amphibolurinae, but much larger in Phrynocephalus vlangalii from the subfamily Agaminae. In most previous studies of these sex chromosomes, the focus has been on Australian species from the subfamily Amphibolurinae, but only the sex chromosomes of the Australian central bearded dragon (Pogona vitticeps) are well-characterized cytogenetically. To determine the level of synteny of the sex chromosomes of P. vitticeps across agamid subfamilies, we performed cross-species two-colour FISH using two bacterial artificial chromosome (BAC) clones from the pseudo-autosomal regions of P. vitticeps. We mapped these two BACs across representative species from all six subfamilies as well as two species of chameleons, the sister group to agamids. We found that one of these BAC sequences is conserved in macrochromosomes and the other in microchromosomes across the agamid lineages. However, within the Amphibolurinae, there is evidence of multiple chromosomal rearrangements with one of the BACs mapping to the second-largest chromosome pair and to the microchromosomes in multiple species including the sex chromosomes of P. vitticeps. Intriguingly, no hybridization signal was observed in chameleons for either of these BACs, suggesting a likely agamid origin of these sequences. Our study shows lineage-specific evolution of sequences/syntenic blocks and successive rearrangements and reveals a complex history of sequences leading to their association with important biological processes such as the evolution of sex chromosomes and sex determination.

Karyotype Characterisation of Two Australian Dragon Lizards (Squamata: Agamidae: Amphibolurinae) Reveals Subtle Chromosomal Rearrangements Between Related Species with Similar Karyotypes

“…Therefore, hybridisation of these BAC clones to study species metaphases would identify sex chromosome homologies. We also confirmed the locations of the 2 P. vitticeps clones, Pv03_L07 as previously mapped and sequenced by Ezaz et al [2013], Young et al [2013], Domaschenz et al [2015] and Alam et al [2020], and also keeping P. vitticeps female metaphase chromosomes as control during the experimentation. BAC Pv116_G15 contains the SF1 gene (Janine Deakin, pers.…”

“…In this study, BAC Pv116_G15 showed similar hybridisation patterns as Pv150_H19 (Fig. 8) by Alam et al [2020]. The sex microchromosomes of P. vitticeps were formed by a translocation of the region containing Pv03_ L07 sequences from the ancestral chromosome 2 [Matsubara et al, 2019].…”

“…We mapped 2 BAC clones to T. lineata and R. diemensis metaphase chromosomes from both sexes. All these (Pv03_L07 and Pv116_G15) were from P. vitticeps Z and W micro sex chromosomes [Ezaz et al, 2013;Domaschenz et al, 2015;Deakin et al, 2016;Alam et al, 2020], while Pv03_L07 also hybridises at the telomeric region of chromosome 2 of P. vitticeps. Therefore, hybridisation of these BAC clones to study species metaphases would identify sex chromosome homologies.…”

“…8e, f). The other BAC clone from P. vitticeps ZW (Pv116_G15) hybridised to a pair of microchromosomes in both sexes of T. lineata and in all individuals of R. diemensis (phenotypic sexes not known), as well as another P. vitticeps ZW BAC clone, Pv150_H19 [Alam et al, 2020]. However, in T. lineata, these BACs do not co-localise with Pv03_L07 signals, and in R. diemensis, they co-localise only with 1 of the 2 pairs, indicating possible chromosomal rearrangements.…”

“…A similar situation might have also occurred in the case of R. diemensis and T. lineata. Alam et al [2020] mapped BAC Pv03_L07 and Pv150_H19 on 12 different species of agamid lizards from all 6 subfamilies, including T. lineata and R. diemensis. They found evidence of multiple chromosomal rearrangements within the Australian Amphibolurinae.…”