Brca2 is involved in meiosis in Arabidopsis thaliana as suggested by its interaction with Dmc1

Two BRCA2-like sequences are present in the Arabidopsis genome. Both genes are expressed in flower buds and encode nearly identical proteins, which contain four BRC motifs. In a yeast two-hybrid assay, the Arabidopsis Brca2 proteins interact with Rad51 and Dmc1. RNAi constructs aimed at silencing the BRCA2 genes at meiosis triggered a reproducible sterility phenotype, which was associated with dramatic meiosis alterations. We obtained the same phenotype upon introduction of RNAi constructs aimed at silencing the RAD51 gene at meiosis in dmc1 mutant plants. The meiotic figures we observed strongly suggest that homologous recombination is highly disturbed in these meiotic cells, leaving aberrant recombination events to repair the meiotic double-strand breaks. The 'brca2' meiotic phenotype was eliminated in spo11 mutant plants. Our experiments point to an essential role of Brca2 at meiosis in Arabidopsis. We also propose a role for Rad51 in the dmc1 context.

Meiosis in flowering plants and other green organisms.

Sexual eukaryotes generate gametes using a specialized cell division called meiosis that serves both to halve the number of chromosomes and to reshuffle genetic variation present in the parent. The nature and mechanism of the meiotic cell division in plants and its effect on genetic variation are reviewed here. As flowers are the site of meiosis and fertilization in angiosperms, meiotic control will be considered within this developmental context. Finally, we review what is known about the control of meiosis in green algae and non-flowering land plants and discuss evolutionary transitions relating to meiosis that have occurred in the lineages giving rise to the angiosperms.

Oscillatory change of SR-protein kinase activities during oocyte maturation meiosis in fish

The SR-protein kinase activity was analyzed and the cytological changes were observed during oocyte maturation in bisexual transparent color crucian carp ( Carassius auratus color variety). The results revealed that the SR-protein kinase activity was sensitive to the artificially induced spawning hormones, and the change of oscillatory activity was similar to that of the maturation-promoting factor (MPF) kinase that regulates meiotic cell cycle in fish.

Role of animal pole protuberance and microtubules during meiosis in sea cucumber Apostichopus japonicus oocytes

Fully grown oocytes of Apostichopus japonicus have a cytoplasmic protuberance where the oocyte attaches to the follicle. The protuberance and the oolamina located on the opposite side of the oocyte indicate the animal-vegetal axis. Two pre-meiotic centrosomes are anchored to the protuberance by microtubules between centrosomes and protuberance. After meiosis reinitiation induced by DTT solution, the germinal vesicle (GV) migrates towards the protuberance. The GV breaks down after it migrates to the oocyte membrane on the protuberance side. The protuberance then contracts back into the oocyte and the first polar body extrudes from the site of the former protuberance. The second polar body forms beneath the first. Thus the oocyte protuberance indicates the presumptive animal pole well before maturation of the oocyte.

Nuclear dispositions of subtelomeric and pericentromeric chromosomal domains during meiosis in asynaptic mutants of rye (Secale cereale L.)

EI Mikhailova, SP Sosnikhina, GA Kirillova, OA Tikholiz, VG Smirnov, RN Jones and G Jenkins (2001). Nuclear dispositions of subtelomeric and pericentromeric chromosomal domains during meiosis in asynaptic mutants of rye (Secale cereale L.). Journal of Cell Science, 114 (10), 1875-1882. Sponsorship: Russian Foundation for Basic Research (grants 00-04-48522/ 99-04-48182) RAE2008

A KARYOLOGICAL DEMONSTRATION OF MEIOSIS IN GELIDIUM-LATIFOLIUM (GELIDIACEAE, RHODOPHYTA) FROM IRELAND

A population of Gelidium latifolium (Greville) Bornet et Thuret (Rhodophyta) from Portstewart, County Antrim, Northern Ireland, was dominated by tetrasporophytes. When grown in culture, excised tips from 10 non-reproductive individuals all formed tetrasporangial branches. Chromosome counts in mitotic nuclei of vegetative cells from cultured tetrasporophytic apices were 58 +/- 4 chromosomes. In nuclei of dividing tetrasporocytes there were 29 +/- 2 larger bodies that were interpreted as paired meiotic chromosomes. Field-collected tetrasporophytes from Islandmagee. County Antrim. also showed approximately 29 pairs of chromosomes during meiosis in tetrasporocytes, This is the first report of meiosis in G. latifolium and the first direct demonstration of meiosis in this commercially important genus. In germinating tetraspores, the haploid nucleus initially divided prior to or during formation of the germination tube. The two daughter nuclei then underwent synchronous mitoses to form four haploid nuclei (n = 29 +/- 2), only one of which entered the germination tube. The sporeling survival rate was low, and few plants grew to maturity. The largest of these was diploid, with 55-58 chromosomes, and formed spermatangia after 14 months in culture. Other plants, which were abnormally bushy and densely branched, failed to reproduce. Since the most vigorous individual (and possibly also the other survivors) had apparently diploidized spontaneously during development, it is possible that the lack of gametophytes in the local G. latifolium population results from poor viability of haploid sporelings.

A cell surface antigen associated with meiosis in male Staurdoderus scalaris (Orthopteran)

Immunofluorescence has identified seven monoclonal antibodies reactive with the surface of meiotic cells and absent in premeiotic cells. Analysis by immunogold electron microscopy indicated that these antigens were present on the external surface of the cells and were coincident with the presence of synaptonemal complexes in the nucleus. On immunoblots a common glycosylated protein of 205 kDa was recognized, in addition to smaller subunits, suggesting the presence of a protein complex comprised of smaller peptides.

Intracellular antigenic changes associated with meiosis in the orthopteran Stauroderus scalaris

Monoclonal antibodies have been prepared against purified pachytene cells from grasshopper testes. Immunoblotting and immunofluorescence analyses identified those monoclonal antibodies which showed specificity for antigens in pachytene cells. Several antigenic changes were found to be associated with meiotic cells. Five monoclonal antibodies detected antigens which were located in the cytoplasm of premeiotic cells but were nuclear during meiosis. One monoclonal antibody showed a discrete cytoplasmic fluorescent pattern in meiotic, but not in premeiotic, cells. Another bound specifically to the nuclei of some epithelial cells at the base of follicles in mature testes.

Meiosis

El v??deo explica el proceso de divisi??n celular mei??tica, necesario para la reproducci??n sexual. Mediante la meiosis obtenemos c??lulas aploides, que son aquellas que contienen la mitad del n??mero de cromosomas y que se forman en los gametos.

Influence of nitric oxide during maturation on bovine oocyte meiosis and embryo development in vitro

The effect of s-nitroso-N-acetyl-1,1-penicillamine (SNAP, a nitric oxide donor) during in vitro maturation (IVM) on nuclear maturation and embryo development was investigated. The effect of increasing nitric oxide (NO) during prematuration or maturation, or both, on embryo development was also assessed. 10(-3) M SNAP nearly blocked oocytes reaching metaphase II (MII) (7%, P < 0.05) while 10(-5) M SNAP showed intermediate proportions (55%). For 10(-7) M SNAP and controls (without SNAP), MII percentages were similar (72% for both, P > 0.05), but superior to the other treatment groups (P < 0.05). Blastocyst development, however, was not affected (38% for all treatments, P < 0.05). TUNEL-positive cells in hatched blastocysts (Day 9) increased when IVM included 10(-5) M SNAP (8 v. 3 to 4 cells in the other treatments, P > 0.05), without affecting total cell numbers (240 to 291 cells, P > 0.05). When oocytes were prematured followed by IVM with or without 10(-7) M SNAP, during either culture period or both, blastocyst development was similar (26 to 40%, P > 0.05). When SNAP was included during both prematuration and IVM, the proportion of Day 9 hatched embryos increased (28% v. 14 to 19% in the other treatments, P < 0.05). Apoptotic cells, however, increased when SNAP was included (6 to 10 cells) in comparison to prematuration and maturation without SNAP (3 cells, P < 0.05). NO may be involved in meiotic progression and apoptosis during embryo development.