The synaptonemal complex as structural framework to integrate cytogenetic and genomic data in birds

PIGOZZI MI

Simposio; XV Inter-American Congress of Microscopy Societies CIASEM XV ? SAMIC VI; 2019

Sociedad Argentina de Microscopia/Committee of the Inter American Society of Microscopy

The possibility to spread synaptonemal complexes (SC) from whole nuclei on a surface for microscopic analyses has been of great benefit to study different features of meiotic prophase and it remains a great tool to observe chromosome behavior in a wide variety of organisms. The existence of a pseudoautosomal region in the sex chromosomes of birds was discovered using electron microscopy to observe SCs and recombination nodules in chicken oocytes. Similar studies in primitive birds concluded that different stages of sex chromosome differentiation co-exist in birds, observations that were later confirmed by genomic analyses of gametologs on the Z and W chromosomes. Direct crossover mapping on pachytene bivalents using fluorescent immunostaining of MLH1 showed that the recombination landscape in birds is quite variable, ranging from nearly homogenous distribution of crossovers along SC arms to strong localization depending on the species. In combination with FISH, crossover mapping on SCs provided a tool to relate physical and genetic distances, giving a reference for linkage mapping. In birds, the value of microscopic analysis of SCs goes beyond the knowledge about autosomes and sex chromosomes. It was in SC spreads that a germ cell restricted chromosome was discovered, first in zebra finches, and later in a large number of passerines, becoming a paradigmatic example that cytogenetics of meiotic cells can be an essential resource for genomics studies.