Meiotic Aberrations Leading To Aneuploidy In Cauliflower (Brassica Oleracea L. var. Botrytis)

Aneuploid cauliflower plants (Brassica oleracea L. var. botrytis) display abnormal curd phenotypes causing serious commercial problems in offspring populations. Despite extensive breeding efforts, selection of genotypes producing euploid gametes remains unsuccessful due to unknown genetic and environmental factors. To reveal the origin of aneuploid gametes, we analyzed chromosome pairing, chiasma formation and chromosome segregation in pollen mother cells of selected cauliflower genotypes. To this end we compared different genotypes exhibiting Low with < 5%, Moderate with 5-10% and High with > 10% aberrant offspring. Microscopic observations revealed regular chromosome pairing at pachytene. However, cells at diakinesis and metaphase I showed variable numbers of univalents, suggesting that chiasma formation during meiotic prophase is incomplete or disrupted and results in a partial desynaptic phenotype. Cells at anaphase I – telophase II exhibited various degrees of unbalanced chromosome numbers explaining the aneuploid offspring. Immunofluorescence probed with an MLH1 antibody demonstrated fluorescent foci in all genotypes, but their lower numbers do not correspond to the putative sites of chiasmata. Interchromosomal connections between chromosomes and bivalents are common at diakinesis and metaphase I, and they contain centromeric and 45S rDNA tandem repeats, but such threads seemed not to affect proper disjoin of the half bivalents at anaphase I. Moreover, male meiosis in the arabidopsis APETALA1/ CAULIFLOWER double mutant with the typical cauliflower phenotype did show interchromosomal connections, but there were no indications for partial desynapsis. We now hypothesize that the occurrence of desynapsis in cauliflower is a developmental out-of-phase phenomenon partially or completely controlled by genes involved in flower and curd development.

Cytological and Cytogenetical Studies on Normal and Interchange Allium Triquetrum

<p>Interchanges (otherwise known as segmental chromosome interchanges or reciprocal translocations), involving exchanges of segments of nonhomologous chromosomes, have been studied extensively in plants. Probably the earliest observations were those of Gates (1903) on a ring of chromosomes at meiosis in Oenothera rubrinervis. Belling's reports of sterility in hybrids amongst certain velvet beans (Stizolobium) were later attributed to an interchange of chromosome segments (Belling, 1925). More clearly defined early cases were provided by McClintock's (1930) cytological demonstrations of interchanges in maize. Burnham's (1956) review indicates a sizable accumulation of data in plants. The researches in maize by Brink, McClintock and Burnham, and others, are by far the most extensive, and these data have contributed much to our present understanding of many cytological processes, particularly synapsis, chiasma formation and orientation phenomena.</p>

Cytological and Cytogenetical Studies on Normal and Interchange Allium Triquetrum

<p>Interchanges (otherwise known as segmental chromosome interchanges or reciprocal translocations), involving exchanges of segments of nonhomologous chromosomes, have been studied extensively in plants. Probably the earliest observations were those of Gates (1903) on a ring of chromosomes at meiosis in Oenothera rubrinervis. Belling's reports of sterility in hybrids amongst certain velvet beans (Stizolobium) were later attributed to an interchange of chromosome segments (Belling, 1925). More clearly defined early cases were provided by McClintock's (1930) cytological demonstrations of interchanges in maize. Burnham's (1956) review indicates a sizable accumulation of data in plants. The researches in maize by Brink, McClintock and Burnham, and others, are by far the most extensive, and these data have contributed much to our present understanding of many cytological processes, particularly synapsis, chiasma formation and orientation phenomena.</p>

Usp26 mutation in mice leads to defective spermatogenesis depending on genetic background

Spermatogenesis is a reproductive system process that produces sperm. Ubiquitin specific peptidase 26 (USP26) is an X chromosome-linked deubiquitinase that is specifically expressed in the testes. It has long been controversial whether USP26 variants are associated with human male infertility. Thus, in the present study, we introduced a mutation into the Usp26 gene in mice and found that Usp26 mutant males backcrossed to a DBA/2 background, but not a C57BL/6 background, were sterile or subfertile and had atrophic testes. These findings indicate that the effects of the Usp26 mutation on male reproductive capacity were influenced by genetic background. Sperm in the cauda epididymis of Usp26 mutant mice backcrossed to a DBA/2 background were decreased in number and showed a malformed head morphology compared to those of wild-type mice. Additionally, histological examinations of the testes revealed that the number of round and elongated spermatids were dramatically reduced in Usp26 mutant mice. The mutant mice exhibited unsynapsed chromosomes in pachynema and defective chiasma formation in diplonema, which presumably resulted in apoptosis of metaphase spermatocytes and subsequent decrease of spermatids. Taken together, these results indicate that the deficiencies in fertility and spermatogenesis caused by mutation of Usp26 were dependent on genetic background.

Induced desynaptic variation in poppy (Papaver somniferum L.)

Cytological investigation of EMS (ethyl methane sulphonate) treated population demonstrated enhanced univalent frequency per cell with unequal separation at Anaphase I. In contrast to controlled plants, medium strong type desynaptic plants were obtained from 0.6 % EMS treated set, revealing high frequency of univalents at Metaphase I, along with bivalents, which were loosely paired. The univalents remained unpaired till the end of meiosis, leading to formation of micronuclei and abnormal tetrads. These plants had high pollen inviability and sterile seeds. It might be possible that EMS had acted on some genes responsible for chiasma formation, resulting in early chiasma dissociation, which suggests that EMS can act as a potential tool in the development of male sterile lines. The study demonstrated the feasibility of chemical mutagenesis in mutation breeding programme on poppy (Papaver somniferum L.).