Immunocytological analysis of meiotic recombination in two anole lizards (Squamata, Dactyloidae)

Abstract

Although the evolutionary importance of meiotic recombination is not disputed, the significance of interspecies differences in the recombination rates and recombination landscapes remains under-appreciated. Recombination rates and distribution of chiasmata have been examined cytologically in many mammalian species, whereas data on other vertebrates are scarce. Immunolocalization of the protein of the synaptonemal complex (SYCP3), centromere proteins and the mismatch-repair protein MLH1 was used, which is associated with the most common type of recombination nodules, to analyze the pattern of meiotic recombination in the male of two species of iguanian lizards, Anolis carolinensis Voigt, 1832 and Deiroptyx coelestinus (Cope, 1862). These species are separated by a relatively long evolutionary history although they retain the ancestral iguanian karyotype. In both species similar and extremely uneven distributions of MLH1 foci along the macrochromosome bivalents were detected: approximately 90% of crossovers were located at the distal 20% of the chromosome arm length. Almost total suppression of recombination in the intermediate and proximal regions of the chromosome arms contradicts the hypothesis that "homogenous recombination" is responsible for the low variation in GC content across the anole genome. It also leads to strong linkage disequilibrium between the genes located in these regions, which may benefit conservation of co-adaptive gene arrays responsible for the ecological adaptations of the anoles.

Keywords: Anolis; Deiroptyx; Reptilia; Synaptonemal complex; chromosomes; crossing over; lizard.

Figure 1.

The SC spreads of Anolis carolinensis (a, b) and Deiroptyx coelestinus (c, d). a, c immunofluorescence and DAPI. Red: SYCP3, green: centromere and MLH1, blue: DAPI b, d DAPI channel separately. Arrowheads show the XY bivalent (Lisachov et al. in press). Arrow shows the DAPI+ band on the SC2 of Deiroptyx coelestinus . Scales bars: 5 µm.

Figure 2.

The distribution of MLH1 foci along the macrochromosomes of Anolis carolinensis and Deiroptyx coelestinus. The X-axis shows the position of MLH1 foci, the marks on this axis are separated by 1 μm. Black dots indicate centromeres. The Y-axis indicates the frequency of MLH1 foci in each 1 μm – interval. Stacked columns show the frequency for the SCs containing MLH1 foci at each interval.