Zlotina A et al. (2017), Amphibian and Avian Karyotype Evolution: Insigh...

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Genes (Basel) 2017 Nov 08;811:. doi: 10.3390/genes8110311.

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Amphibian and Avian Karyotype Evolution: Insights from Lampbrush Chromosome Studies.

Zlotina A , Dedukh D , Krasikova A .

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Amphibian and bird karyotypes typically have a complex organization, which makes them difficult for standard cytogenetic analysis. That is, amphibian chromosomes are generally large, enriched with repetitive elements, and characterized by the absence of informative banding patterns. The majority of avian karyotypes comprise a small number of relatively large macrochromosomes and numerous tiny morphologically undistinguishable microchromosomes. A good progress in investigation of amphibian and avian chromosome evolution became possible with the usage of giant lampbrush chromosomes typical for growing oocytes. Due to the giant size, peculiarities of organization and enrichment with cytological markers, lampbrush chromosomes can serve as an opportune model for comprehensive high-resolution cytogenetic and cytological investigations. Here, we review the main findings on chromosome evolution in amphibians and birds that were obtained using lampbrush chromosomes. In particular, we discuss the data on evolutionary chromosomal rearrangements, accumulation of polymorphisms, evolution of sex chromosomes as well as chromosomal changes during clonal reproduction of interspecies hybrids.

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	Figure 1. Comparison of the usage of amphibian lampbrush chromosome (a,b) and metaphase chromosome (c), for high-resolution fluorescent in situ hybridization (FISH)-mapping. Lampbrush chromosomes exhibit marker loops (indicated by arrows in (a)) and other landmarks (including nucleolus, nu in (a,b)), which allows to construct cytological chromosomal maps (d). Such maps facilitate identification of individual chromosomes and their particular regions. Mapping of interstitial telomeric sites (shown by square brackets) in: lampbrush chromosome (b); and metaphase chromosome (c). Arrowheads indicate centromeres. Chromosomes are counterstained with DAPI (4′ 6-diamidino-2-phenylindole). Scale bar = 10 µm.
	Figure 2. High-resolution FISH-mapping on avian lampbrush chromosomes (an example). FISH with chicken nuclear-membrane-associated repeat (CNM repeat)-specific probe (red) and bacterial artificial chromosome (BAC) clones WAG12C15 (green) and WAG30L03 (yellow) on chicken lampbrush chromosome 3. Chromosome is counterstained with DAPI. Scale bar = 10 μm. Chromosome coordinates of BACs and CNM clusters are given in megabases (Mb) according to the chicken genome assembly Gallus_gallus-5.0 (https://www.ncbi.nlm.nih.gov/genome/111) [26]. BACs were kindly provided by Richard Crooijmans and Martin Groenen (Wageningen chicken BAC library, Crooijmans et al., 2000 [29]). The data on precise genome positioning of the centromere and two CNM-repeat clusters from chicken chromosome 3 are published in Zlotina et al., 2010 [54].
	Figure 3. Example of lampbrush chromosome application to study chromosomal rearrangements. Inverted order of marker structures (special loops and granules) indicates the inversion of a chromosomal segment. Additional marker structures appear after accumulation of genetic polymorphisms in the absence of recombination.

References [+] :

Bi, Probing the meiotic mechanism of intergenomic exchanges by genomic in situ hybridization on lampbrush chromosomes of unisexual Ambystoma (Amphibia: Caudata). 2010, Pubmed