Evidence on the time of chromosome pairing from the preleptotene spiral stage in Lilium longiflorum ?Croft?

Walters, Marta Sherman

doi:10.1007/bf00281923

Cited by 60 publications

(22 citation statements)

References 53 publications

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“…At this stage the heterochromatin has doubled in volume (see section 3.5) and beside the heterogenous larger chromocenters bipartite chromocenters can be recognized. Extreme condensation of the chromatin, as described for the late interphase-early leptotene stage in certain Lilium hybrids and varieties (5,6,74,75) has never been observed in this clone. As the leptotene chromosomes thicken the heterochromatic lumps disappear successively (Figure 2f …”

Section: Light Microscopic Morphology Of Presynaptic Stagesmentioning

confidence: 47%

“…Histone synthesis has been reported to be uncoupled from DNA replication at this stage (8,66), and a histone unique to meiosis with properties similar to the H 1 histone is synthesized (60). The chromatin has been reported to undergo compaction before the leptotene stage (5,6,74,75) similar to the situation in other organisms (10,25). During the presynaptic interval in Lilium a succession of stages is identifiable by distinctive changes in the organization of the heteroehromatin and the nucleoli, and it has been suggested that the premeiotic heterochromatin might have an impact on the control of the crossing-over process (65).…”

Section: Introductionmentioning

confidence: 96%

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The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

Holm

1977

Carlsberg Res. Commun.

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The presynaptic stages of Lilium longiflorum have been analyzed in the light microscope. Seven substages can be defined on the basis of changes in morphology of the heterochromatin and the nucleoli. The duration of the presynaptic interval and the substages has been calculated from bud length measurements and cell stage gradients in the anthers. The premeiotic and somatic DNA replication has been investigated using 3H-thymidine autoradiography. The premeiotic S phase lasts 50 hours whereas the somatic S phase in root tip nuclei is six times shorter. Moreover, premeiotic S phase nuclei house 2-3 times more heterochromatin than somatic nuclei. The premeiotic DNA replication can be divided into three periods: In early S phase the DNA of euchromatin is replicated; in mid S phase synthesis is arrested for a minimum of 9 hours; and in late S phase the DNA of heterochromatin is replicated. DNA synthesis in heterochromatin is correlated with a dispersal of these chromatin regions. Determinations of volume and staining characteristics of heterochromatin after the application of C and Q banding procedures indicate that the premeiotic heterochromatin comprises C bands, Q bands and interbands. The premeiotic DNA replication is discussed in relation to the observed chromatin dynamics, and a proposal is made for the significance of the replication sequence to the formation of the leptotene chromosome and the control of crossing-over.

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Section: Light Microscopic Morphology Of Presynaptic Stagesmentioning

confidence: 47%

Section: Introductionmentioning

confidence: 96%

The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

Holm

1977

Carlsberg Res. Commun.

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“…This is certainly not the case in those organisms where leptotene and zygotene nuclei have been reconstructed. A number of investigations including the present one have unequivocally demonstrated that homologous chromosomes are either distributed in different regions of the nucleus prior to the initiation of pairing at leptotene (14,19,40,48) or even located in separate nuclei (28,49,53).…”

Section: Interlockingmentioning

confidence: 56%

Human meiosis II. Chromosome pairing and recombination nodules in human spermatocytes

Rasmussen

Holm

1978

Carlsberg Res. Commun.

146

161

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Meiosis in human spermatocytes has been analyzed by three dimensional reconstructions of 4 leptotene, 4 earlymid zygotene, 10 late zygotene, and 21 early pachytene nuclei. At leptotene, a lateral component is organized along each chromosome and the telomeres attach to the nuclear envelope. At early zygotene, the attachment sites aggregate and a chromosome bouquet is formed. Pairing and synaptonemal complex formation are initiated from the telomeres by binding of precursor material for the central region to the lateral components of the aligned homologues. In the 10 late zygotene nuclei, on the average 72% of the autosomal complement had been paired. Synaptonemal complex formation is in most cases initiated from both ends of the homologues and only in 5 cases was initiation of complex formation interstitial. Pairing of the short arms of the acrocentric bivalents and the X and Y chromosomes is delayed compared to the remainder of the genome. Irregularities such as interlockings and breaks of the lateral components of chromosomes or breaks of the synaptonemal complexes of bivalents are observed in 8 out of the 10 nuclei. Most of the breaks appeared to be the result of a resolution of interlockings. At early pachytene, all bivalents are fully paired the only exception being the secondary constrictions on bivalents 1 and 9 which frequently remain unpaired. In all nuclei, a short stretch of synaptonemal complex is present between the X and Y chromosomes. Only two interlockings and three breaks of lateral components of chromosomes were found at this stage. Recombination nodules are present in or at the central region of the synaptonemal complex from early zygotene and evidence has been obtained in favor of an attachment of nodules to precursor material for the central region at the pairing fork. Nodules can, however, also attach to a fully formed synaptonemal complex. At late zygotene, an average number of 101 nodules per nucleus is present. Assuming that all regions of the complex have equal probabilities of receiving a nodule about 144 nodules are expected to be present at the moment of complete pairing. At early pachytene, the mean number of nodules is 75. Generally, nodules appear to be distributed evenly along the bivalent arms. Nodules are present, however, in excess in the telomere regions and in the XY bivalent while the centromere regions, the secondary constrictions, and the short arms of the acroeentric bivalents are relatively depleted of nodules. Measurements of the distances between adjacent nodules and a comparison with a theoretical distribution of such distances assuming a random positioning of nodules have demonstrated that at late zygotene nodules are more frequently clustered than would be expected if they were distributed independently. At early pachytene, the reverse pattern is observed.

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“…In Lilium, heterochromatinization in preleptotene meiocytes has been described recently by Walters (8,16). Nucleolar transformations have been reported by Moens, using both light and electron microscopy (17).…”

Section: The Hypothesismentioning

confidence: 87%

Presynaptic events in meiocytes of Lilium longiflorum and their relation to crossing-over: a preselection hypothesis.

Stern¹,

Westergaard²,

Wettstein³

1975

Proc. Natl. Acad. Sci. U.S.A.

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We are proposing a "Preselection Hypothesis" to account for the regulation of crossing-over in eukaryotic organisms. The hypothesis characterizes meiosis in terms of three major physiological stages: (1) a presynaptic stage when pairs of homologous DNA stretches are selected so as to become trapped within the synaptinemal complex during synapsis, (2) an alignment of homologous chromosomes and stabilization of paired bivalents via the synaptinemal complex, and (3) a scission and rejoining of DNA stretches leading to the formation of chiasmata and crossovers. The hypothesis centers on the first stage and is based on evidence for the occurrence of significant cytological and biochemical changes prior to synapsis. The major feature of the hypothesis is that crossing-over occurs only in trapped DNA stretches. Thus, potential crossing-over sites, though not crossingover itself, are determined well before chromosomes pair. Since, to a large degree, crossovers are distributed randomly along the length of each chromosome, the preselection process must result in a random assortment of trapped DNA stretches, the assortment differing from one meiocyte to another.The principal challenge in explaining crossing-over in eukaryotes is not so much the molecular mechanism of exchange between DNA strands as the mode of organization by which these exchanges are regularly effected in meiotic cells. Although prokaryotes provide a system of choice for probing the immediate events of DNA recombination, eukaryotes house facilitating mechanisms that are superimposed on the pure process of molecular recombination. The juxtapositioning of homologous chromosomes whose DNA lengths may exceed one meter, the apparent exclusion of sister-chromatid exchanges in the face of closely aligned sisters and homologs, the organization of homologous chromatids to accommodate four-strand crossing-over, the regulated distribution of exchanges as manifested in positive interference, and the restriction of the total process to differentiated meiocytes are specific items in the complex calendar of events governing meiotic recombination in eukaryotes. ConsiderationsAlthough some uncertainty exists about the precise time at which strand exchanges occur in relation to the formation of the synaptinemal complex (SC), there can be little doubt that DNA strands transverse the complex at crossover sites. Unless crossing-over precedes synapsis, a possibility that we summarily set aside, its occurrence must be restricted to situations in which homologous regions are closely juxtaposed Abbreviation: SC, synaptinemal complex. within the SC. Such situations, however, would only allow for a very small proportion of DNA to engage in crossing-over. This follows from the morphology of the pachytene bivalent. Generally, "the SC joins homologous chromosomes over their whole length" (1). However, in the three species so far analyzed, namely Neurospora crassa (2), Drosophila melanogaster (3), and Zea mays (4), the length ratios of SC to chromosome DNA were about 0.3%, 0.2%...

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Evidence on the time of chromosome pairing from the preleptotene spiral stage in Lilium longiflorum ?Croft?

Cited by 60 publications

References 53 publications

The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

Human meiosis II. Chromosome pairing and recombination nodules in human spermatocytes

Presynaptic events in meiocytes of Lilium longiflorum and their relation to crossing-over: a preselection hypothesis.

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