Surface Spreads Of Synaptonemal Complexes Research Articles

Surface Spreading Technique in Plant Meiocytes for Analysis of Synaptonemal Complex by Electron Microscopy.

An improved method of preparing two-dimensional surface spreads of synaptonemal complexes (SCs) in higher plants for examination by electron microscopy is described. This protocol produces clear, well-spread preparations of SCs and unpaired axial cores from a range of meiotic prophase I stages (leptotene to pachytene) from meiocytes of different plant species. Synaptonemal complex (SC) analyses have been widely used in plant cytogenetic studies to address the process of meiotic chromosome synapses, because of the high-resolution allowed by electron microscopy. Although the real role of SC is still enigmatic, its presence and structural conservation in the vast majority of organisms reflect the importance of this protein structure in the meiotic process.

Surface spreading of synaptonemal complexes in the clam Dosinia exoleta (Mollusca, Bivalvia)

There are only a few reports on the chromosomal location of DNA sequences in bivalve species, none of them using meiotic chromosomes. Mitotic chromosomes of the clam Dosinia exoleta were analysed by means of Giemsa, silver and fluorochrome staining and fluorescent in situ hybridization (FISH) with 18S + 28S rDNA and telomeric probes. A technique for surface spreading of synaptonemal complexes (SCs) of Dosinia exoleta was developed for the first time in a bivalve species. Silver and DAPI/PI staining and SC-FISH were also applied to the study of the meiotic chromosomes of this clam. The diploid chromosome number in this species is 38 and the karyotype is composed of 11 pairs of metacentric and eight pairs of submetacentric chromosomes. 18S + 28S rDNA clusters map to the subtelomeric region of the short arm of one metacentric chromosome pair whereas telomeric signals appear at both ends of every chromosome.

The pattern of zygotene and pachytene pairing in allotetraploid Aegilops species sharing the U genome

Allotetraploid Aegilops species sharing the U genome, Ae. columnaris (UUMM), Ae. ovata (UUMM), Ae. triaristata (UUMM), Ae. triuncialis (UUCC) and Ae. variabilis (UUSS), regularly form bivalents at metaphase I of meiosis. The pattern of zygotene and pachytene pairing was analyzed by whole-mount surface-spreading of synaptonemal complexes under the electron microscope. The data indicated that at the zygotene stage the chromosomes were almost exclusively associated as bivalents; only a few multivalents (7%) were observed. These observations are discussed in relation to mechanisms of diploidization of polyploid meiosis.

Synaptic patterns of rye B chromosomes. IV. The B isochromosomes

Pairing of B isochromosomes in rye was studied by surface spreading of synaptonemal complexes in pollen mother cells from plants containing one small iso-B (iso-BS), one large iso-B (iso-BL), two iso-BL, one iso-BS plus one standard B (iso-BS+stB), one iso-BS plus two standard Bs (iso-BS + 2 stB) and one iso-BL plus two standard Bs (iso-BL + 2 stB). The main characteristics of iso-Bs were as follows. (1) Their location in the surface-spread nuclei was peripheral. (2) Their period of pairing relative to that of the A-set was delayed. (3) The commonest pachytene configuration was a symmetrical hairpin loop, although they could also undergo nonhomologous synapsis. (4) Synapsis could start at the chromosome ends, at the putative centromeric region or at both regions more or less simultaneously. (5) The frequency of iso-BL bivalents was only 46 per cent rather than the 66 per cent predicted by the random-end-pairing model. Interchromosomal pairing was frequent in these configurations. (6) In pairing competition situations involving three and four doses of the short arm of the standard B (iso-BS+stB, iso-BS + 2 stB), a large predominance of self-synapsed iso-BS univalents (63 per cent and 80 per cent respectively) was found. On the other hand, there was no apparent pairing preference among four doses of the long arm of the standard B in the iso-BL + 2 stB combination. Similarities and differences between the synaptic behaviours of iso-Bs of Crepis capillaris and Secale cereale are discussed.

Synaptic patterns of rye B chromosomes. III. The deficient B.

Chromosomal pairing of a deficient B chromosome in rye has been studied by surface spreading of synaptonemal complexes in pollen mother cells from plants containing one deficient B (dB), one deficient B plus one standard B (dBstB) and one deficient B plus two standard Bs (dB2stB). Single dBs are often located peripherally in surface spread nuclei, and they undergo extensive non-homologous synapsis at pachytene. In the dBstB bivalents, homologous and non-homologous synapses occur simultaneously throughout pachytene without axial equalization. Competition for pairing between the dB and the two stBs results in a large predominance (80%) of stB bivalents. This finding is explained by the identical origin of the standard Bs and/or by the minor homology between the stB and the dB chromosomes.

Elimination of synaptonemal complex irregularities in a Lolium hybrid

The diploid hybrid ryegrass, Lolium temulentum × L. perenne (2n = 14), contains two sets of chromosomes which are structurally and genetically dissimilar. Whole-mount surface spreading of synaptonemal complexes from 35 pollen mother cell nuclei shows that chromosome pairing during meiotic prophase is highly irregular, with homoeologues and heterologues pairing together to form multivalents. These are eliminated, however, during meiotic prophase in favour of homoeologous bivalents. In addition, the length differential between homoeologous chromosomes is accommodated in a coordinated fashion and is absorbed into the structure of the synaptonemal complexes. The hybrid thus displays a remarkable capacity to eliminate synaptonemal complex irregularities and to produce homoeologous bivalents, which are functionally and morphologically almost indistinguishable from their homologous counterparts in the parents.

Elimination of multivalents during meiotic prophase in Scilla autumnalis. I. Diploid and triploid

The ultrastructure and pairing behaviour of the chromosomes of two diploid cytotypes and a triploid of Scilla autumnalis were investigated using the techniques of three-dimensional reconstruction from serial electron micrographs and whole-mount surface spreading of synaptonemal complexes. The diploids, designated AA and B7B7, have karyotypes that are virtually identical in appearance at mitotic metaphase but differ in length by 47% and in DNA content by 66%. All the chromosomes were identified during meiotic prophase in both diploids, enabling construction of accurate karyotypes, which were the same as those derived from root tip metaphases. Chromosome pairing was largely regular with very few structural chromosome rearrangements. These two observations permitted confident interpretations of multivalent configurations observed in polyploids containing multiples of the A and B7 genomes. In the triploid (AB7B7) during meiotic prophase lateral components are associated in groups of three, either as trivalents with several exchanges of pairing partners, or as bivalents and univalents in close alignment. The overall difference in length between A and B7 chromosomes is close to expected, but varies to some degree depending on the extent of pairing between the two chromosome types. Most of the synaptonemal complexes between A and B7 homoeologues are ineffective in terms of chiasma formation, as revealed by the low frequency of multivalents and heteromorphic bivalents at metaphase I. In other words, there is an elimination of multivalents during meiotic prophase in the triploid.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination.

Surface spreading of synaptonemal complexes in three isopod crustacean species

The technique of whole mount spreading is used to investigate the SC of three species of Asellidae (isopod crustaceans), Asellus aquaticus, Proasellus coxalis and Proasellus meridianus, which display considerable differences in genomic DNA content. The three species, originally considered to belong to the same genus Asellus, were subsequently assigned to two separate genera: Asellus and Proasellus. The SCs of the three species differ in morphological details related to the shape of the centromere region, the attachments to the nuclear envelope, the width of the central region and the presence of twists of the lateral elements. Furthermore, they display some differences in the degree of compaction of genomic DNA in the mitotic chromosomes. The greatest differences are found between A. aquaticus and P. coxalis, while P. meridianus has several features in common with either species.

Surface spreading of synaptonemal complexes in locusts

The patterns of meiotic pairing initiation and progression in Locusta migratoria and Schistocerca gregaria are described from observations on surface-spread zygotene stage nuclei. In both species pairing is initiated from proximal and distal chromosomal ends, but in addition some interstitial points of pairing initiation also occur, particularly in the longer chromosomes. The details of pairing behaviour are to some extent variable and characteristic for the different species and different chromosomes. There is a pronounced length-dependent sequence of pairing among chromosomes which is especially marked in Locusta: the shorter chromosomes commence and finish pairing relatively early. The patterns of pairing initiation and chiasma formation, in both species, show some similarities but they do not correspond closely. The implications of these findings for the regulation of chiasma number and position are discussed.

Surface spreading of synaptonemal complexes in locusts

Surface spreading of synaptonemal complexes in locusts

A method for preparing two-dimensional surface-spreads of synaptonemal complexes from plant meiocytes for light and electron microscopy

A method has been developed for preparing two-dimensional surface spreads of synaptonemal complexes (SCs) from plant meiocytes for examination by light and/or electron microscopy. Clear, well-spread preparations of SCs and unpaired axial cores have been obtained from a range of meiotic prophase I stages (leptotene to pachytene) from Allium and Secale meiocytes.