scholarly journals Quantifying Meiosis: Use of the Fractal Dimension, Df, to Describe and Predict Prophase I Substages and Metaphase I

10.5772/29389 ◽  
2012 ◽  
Author(s):  
Cynthia Ross ◽  
Hua-Feng Wang
Keyword(s):  
Fractal Dimension ◽  
Prophase I ◽  
Metaphase I

Chromosome pairing and potential for intergeneric recombination in some hypotetraploid somatic hybrids of Lycopersicon esculentum (+) Solanum tuberosum

Genome ◽  
1993 ◽  
Vol 36 (6) ◽  
pp. 1032-1041 ◽  
Author(s):  
J. H. de Jong ◽  
A. M. A. Wolters ◽  
J. M. Kok ◽  
H. Verhaar ◽  
J. van Eden
Keyword(s):  
Solanum Tuberosum ◽  
Lycopersicon Esculentum ◽  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Somatic Hybrids ◽  
Cytogenetic Study ◽  
Unreduced Gametes ◽  
Root Tip ◽  
Prophase I ◽  
Metaphase I

Three somatic hybrids resulting from protoplast fusions of a diploid kanamycin-resistant line of tomato (Lycopersicon esculentum) and a dihaploid hygromycin-resistant transformant of a monohaploid potato (Solanum tuberosum) line were used for a cytogenetic study on chromosome pairing and meiotic recombination. Chromosome counts in root-tip meristem cells revealed two hypotetraploids with chromosome complements of 2n = 46 and one with 2n = 47. Electron microscope analyses of synaptonemal complex spreads of hypotonically burst protoplasts at mid prophase I showed abundant exchanges of pairing partners in multivalents involving as many as eight chromosomes. In the cells at late pachytene recombination nodules were found in multivalents on both sides of pairing partner exchanges, indicating recombination at both homologous and homoeologous sites. Light microscope observations of pollen mother cells at late diakinesis and metaphase I also revealed multivalents, though their occurrence in low frequencies betrays the reduction of multivalent number and complexity. Precocious separation of half bivalents at metaphase I and lagging of univalents at anaphase I were observed frequently. Bridges, which may result from an apparent inversion loop found in the synaptonemal complexes of a mid prophase I nucleus, were also quite common at anaphase I, though the expected accompanying fragments could be detected in only a few cells. Most striking were the high frequencies of first division restitution in preparations at metaphase II/anaphase II, giving rise to unreduced gametes. In spite of the expected high numbers of balanced haploid and diploid gametes, male fertility, as revealed by pollen staining, was found to be negligible.Key words: synaptonemal complex, recombination, chromosome pairing, somatic hybrid, Lycopersicon esculentum (+) Solanum tuberosum.

The chromosome numbers of five North American and European leech species

1987 ◽  
Vol 65 (3) ◽  
pp. 681-684 ◽  
Author(s):  
Ronald W. Davies ◽  
R. N. Singhal
Keyword(s):  
Chromosome Number ◽  
North American ◽  
Chromosome Numbers ◽  
Chromosome Evolution ◽  
Chromosome Counts ◽  
Prophase I ◽  
Metaphase I

Chromosome counts were obtained for four glossiphoniid species belonging to three genera (Glossiphonia, Theromyzon, Placobdella) and for one erpobdellid species (Dina lineata) of freshwater leeches. Theromyzon rude, which has a Palaearctic distribution, had seven bivalents at prophase I and metaphase I, while the Holarctic T. tessulatum had eight bivalents, giving diploid chromosome numbers of 14 and 16, respectively. Placobdella papillifera from Alberta had a chromosome number of 2n = 24 and Glossiphonia complanata from Alberta and England had chromosome counts of 2n = 28. At prophase I and metaphase I nine bivalents occurred in the majority of the nuclei of Dina lineata. These findings are discussed in relation to the chromosome evolution and phylogenetic schemes proposed by previous authors.

scholarly journals SKP1 drives the prophase I to metaphase I transition during male meiosis

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz2129 ◽  
Author(s):  
Yongjuan Guan ◽  
N. Adrian Leu ◽  
Jun Ma ◽  
Lukáš Chmátal ◽  
Gordon Ruthel ◽  
...  
Keyword(s):  
Okadaic Acid ◽  
Meiotic Prophase ◽  
Essential Role ◽  
Male Meiosis ◽  
Prophase I ◽  
Ubiquitin E3 Ligase ◽  
Competence Factor ◽  
Competence Acquisition ◽  
Mi Transition ◽  
Metaphase I

The meiotic prophase I to metaphase I (PI/MI) transition requires chromosome desynapsis and metaphase competence acquisition. However, control of these major meiotic events is poorly understood. Here, we identify an essential role for SKP1, a core subunit of the SKP1–Cullin–F-box (SCF) ubiquitin E3 ligase, in the PI/MI transition. SKP1 localizes to synapsed chromosome axes and evicts HORMAD proteins from these regions in meiotic spermatocytes. SKP1-deficient spermatocytes display premature desynapsis, precocious pachytene exit, loss of PLK1 and BUB1 at centromeres, but persistence of HORMAD, γH2AX, RPA2, and MLH1 in diplonema. Strikingly, SKP1-deficient spermatocytes show sharply reduced MPF activity and fail to enter MI despite treatment with okadaic acid. SKP1-deficient oocytes exhibit desynapsis, chromosome misalignment, and progressive postnatal loss. Therefore, SKP1 maintains synapsis in meiosis of both sexes. Furthermore, our results support a model where SKP1 functions as the long-sought intrinsic metaphase competence factor to orchestrate MI entry during male meiosis.

Synaptic abnormalities in spread nuclei of Secale. II. Secale vavilovii

Genome ◽  
1995 ◽  
Vol 38 (4) ◽  
pp. 772-779 ◽  
Author(s):  
M. Martínez ◽  
C. Romero ◽  
C. Cuadrado
Keyword(s):  
Synaptonemal Complex ◽  
High Frequency ◽  
Diploid Species ◽  
Chromosome Complement ◽  
Nucleolar Organizer ◽  
Prophase I ◽  
Total Length ◽  
Metaphase I

Secale vavilovii PMCs have more univalents and a lower frequency of bound arms at metaphase I than other diploid Secale species. The spreading technique applied at prophase I showed that the nuclei were able to complete synapsis at pachytene. However, 25% of the nuclei analyzed, which had more than 90% of their total length paired, showed two abnormalities: long fold-back loops, which were located mainly on the nucleolar organizer bivalent, and pairing-partner switches, probably involving all the chromosome complement. These synaptic abnormalities are unusual in diploid species and give rise to a high frequency of nonhomologous pairing regions and, therefore, could produce desynapsis, which could explain the data obtained from metaphase I. The possible origin of the unusual synaptic abnormalities of S. vavilovii is discussed.Key words: S. vavilovii, synaptonemal complex, spreading, synaptic abnormalities.

scholarly journals Two UV-sensitive targets in dorsoanterior specification of frog embryos

Development ◽  
1989 ◽  
Vol 106 (3) ◽  
pp. 511-518 ◽  
Author(s):  
R.P. Elinson ◽  
P. Pasceri
Keyword(s):  
Uv Irradiation ◽  
Normal Development ◽  
Lithium Treatment ◽  
Dorsoventral Polarity ◽  
Prophase I ◽  
Uv Dose ◽  
Metaphase I

Previous work has shown that ultraviolet (UV) irradiation of fertilized frog eggs yields embryos that lack dorsal and anterior structures. The eggs fail to undergo the cortical/cytoplasmic rotation that specifies dorsoventral polarity, and they lack an array of parallel microtubules associated with the rotation. These eggs can be rescued by tilting with respect to gravity, and normal dorsoanterior development occurs. We find here that UV irradiation of Xenopus prophase I oocytes or Rana metaphase I oocytes also causes the dorsoanterior deficient syndrome, but the UV target is different from that in fertilized eggs. Tilting eggs, irradiated as oocytes, with respect to gravity, does not rescue dorsoanterior development, although lithium treatment does. The UV dose required to produce dorsoanterior deficiency for Rana metaphase I oocytes is much less than that for fertilized eggs, and the oocytes can form the array of parallel microtubules and undergo the cortical/cytoplasmic rotation after fertilization. Despite these features of normal development, no dorsoanterior structures form. While the UV target in fertilized eggs is thought to be the parallel microtubules (Elinson & Rowning, 1988; Devl Biol. 128, 185–197), the UV target in the oocytes may be a dorsal determinant.

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Genome ◽  
1999 ◽  
Vol 42 (4) ◽  
pp. 662-667
Author(s):  
M Martínez ◽  
C Cuadrado ◽  
J Sybenga ◽  
C Romero
Keyword(s):  
Electron Microscopy ◽  
Synaptonemal Complex ◽  
Prophase I ◽  
Quadrivalent Frequency ◽  
Surface Spread ◽  
Metaphase I

Synaptic behaviour of the two tetraploids rye cultivars Gigantón (G) and Tetrapico (T) displaying significant differences in their quadrivalent frequencies at metaphase I was analyzed by electron microscopy in surface-spread prophase I nuclei. A different behaviour was observed between the two cultivars; the synaptonemal complex (SC) quadrivalents frequency being significantly higher in G than in T at prophase I. Moreover, the G SC quadrivalents had more synaptic partner exchanges (SPEs) and their location was more distal than the T SC quadrivalents. However, inverse findings were found at metaphase I, the quadrivalent frequency was higher in T than in G. The role that different factors, mainly the number and location of the SPEs and the frequency and distribution of chiasmata, could play in the evolution from prophase I to metaphase I in both cultivars is discussed.Key words: autotetraploid rye, synaptonemal complex, spreading.

Meiosis in allopolyploid Crepis capillaris. II. Autotetraploids

Genome ◽  
1994 ◽  
Vol 37 (3) ◽  
pp. 497-505 ◽  
Author(s):  
G. H. Jones ◽  
J. E. Vincent
Keyword(s):  
Meiotic Chromosome ◽  
Positional Distribution ◽  
Chromosome Size ◽  
High Frequencies ◽  
Crepis Capillaris ◽  
Prophase I ◽  
Direct Observations ◽  
Surface Spread ◽  
Pairing Initiation ◽  
Metaphase I

Meiotic chromosome pairing of autotetraploid Crepis capillaris was analysed by electron microscopy of surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I chromosome configurations. Prophase I quadrivalent frequencies are high in all three tetrasomes. (A, D, and C) and partially dependent on chromosome size. At metaphase I quadrivalent frequencies are much lower and strongly dependent on chromosome size. There is no evidence for multivalent elimination during prophase I in this system, and the reduction in multivalent frequency at metaphase I can be explained by an insufficiency of appropriately placed chiasmata. The high frequencies of prophase I quadrivalents far exceed the two-thirds expected on a simple model with two terminal independent pairing initiation sites per tetrasome, suggesting that multiple pairing initiation occurs. Direct observations reveal relatively high frequencies of pairing partner switches (PPSs) at prophase I, which confirms this suggestion. The numbers of PPSs per tetrasome show a good fit to the Poisson distribution, and their positional distribution along chromosomes is random and nonlocalized. These observations favour a model of pairing initiation based on a large number of evenly distributed autonomous pairing sites each with a uniform and low probability of generating a PPS.Key words: autotetraploid, meiosis, Crepis capillaris, multivalent, pairing partner switch.

Analysis of the mechanism(s) of metaphase I arrest in maturing mouse oocytes

Development ◽  
1995 ◽  
Vol 121 (4) ◽  
pp. 925-933 ◽  
Author(s):  
A. Hampl ◽  
J.J. Eppig
Keyword(s):  
Oocyte Maturation ◽  
Kinase Activity ◽  
Regulatory Protein ◽  
Cyclin B ◽  
Meiotic Maturation ◽  
Prophase I ◽  
Mouse Oocytes ◽  
Metaphase I

Fully grown mouse oocytes are normally competent to progress from prophase I to metaphase II without interruption. However, growing mouse oocytes initially become only partially competent to undergo meiotic maturation. Meiotic maturation in these oocytes does not progress beyond metaphase I. In contrast to the oocytes of most strains of mice, most oocytes of strain LT/Sv mice become arrested at metaphase I even when they are fully grown. The initiation of oocyte maturation is correlated with an increase in p34cdc2 kinase activity that continues to rise until metaphase I. The transition into anaphase I is normally correlated with a decrease in p34cdc2 kinase activity. This study demonstrated that metaphase I arrest in both partially competent growing oocytes and fully grown LT/Sv oocytes is correlated with a sustained elevation of p34cdc2 kinase activity. In fact, p34cdc2 activity continued to increase during the time when activity normally decreased. In normally maturing oocytes, some, but not all, of the cyclin B, the regulatory protein associated with p34cdc2, became degraded in oocytes that entered anaphase I. In contrast, the amount of cyclin B present in the metaphase I-arrested oocytes continued to increase at the time when it was being degraded in normal oocytes progressing to metaphase II. These results suggest that the progression of meiosis is arrested at metaphase I in both groups of oocytes because of continued p34cdc2 kinase activity sustained, at least in part, by restricted degradation of cyclin B.(ABSTRACT TRUNCATED AT 250 WORDS)

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