Limits...
Telomeres cluster de novo before the initiation of synapsis: a three-dimensional spatial analysis of telomere positions before and during meiotic prophase.

Bass HW, Marshall WF, Sedat JW, Agard DA, Cande WZ - J. Cell Biol. (1997)

Bottom Line: We found that nuclei at the last somatic prophase before meiosis exhibit a nonrandom, polarized chromosome organization resulting in a loose grouping of telomeres.The stage-dependent changes in telomere arrangements are suggestive of specific, active telomere-associated motility processes with meiotic functions.Thus, the formation of the cluster itself is an early event in the nuclear reorganizations associated with meiosis and may reflect a control point in the initiation of synapsis or crossing over.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California at Berkeley 94720, USA.

ABSTRACT
We have analyzed the progressive changes in the spatial distribution of telomeres during meiosis using three-dimensional, high resolution fluorescence microscopy. Fixed meiotic cells of maize (Zea mays L.) were subjected to in situ hybridization under conditions that preserved chromosome structure, allowing identification of stage-dependent changes in telomere arrangements. We found that nuclei at the last somatic prophase before meiosis exhibit a nonrandom, polarized chromosome organization resulting in a loose grouping of telomeres. Quantitative measurements on the spatial arrangements of telomeres revealed that, as cells passed through premeiotic interphase and into leptotene, there was an increase in the frequency of large telomere-to-telomere distances and a decrease in the bias toward peripheral localization of telomeres. By leptotene, there was no obvious evidence of telomere grouping, and the large, singular nucleolus was internally located, nearly concentric with the nucleus. At the end of leptotene, telomeres clustered de novo at the nuclear periphery, coincident with a displacement of the nucleolus to one side. The telomere cluster persisted throughout zygotene and into early pachytene. The nucleolus was adjacent to the cluster at zygotene. At the pachytene stage, telomeres rearranged again by dispersing throughout the nuclear periphery. The stage-dependent changes in telomere arrangements are suggestive of specific, active telomere-associated motility processes with meiotic functions. Thus, the formation of the cluster itself is an early event in the nuclear reorganizations associated with meiosis and may reflect a control point in the initiation of synapsis or crossing over.

Show MeSH
Telomere distribution at the bouquet stage. Sequential color overlay projections of four nuclei subjected to telomere FISH are  shown for the DAPI (DNA, red) and FITC (telomeres, green) images as described in Fig. 3. (A and B) Nuclei identified to be at the  “early bouquet” stage (see Results and Discussion) show clustering of telomeres at the nuclear periphery. The nucleolus (n) is remote  from the base of the bouquet (bb) in these early bouquet nuclei. (C and D) Two representative zygotene nuclei show colocalization of  the base of the bouquet with the nucleolus (n). Gray scale images of knobs are included (insets with arrows) to illustrate the spherical  (A) and elongated (D) shapes of these heterochromatic blocks, features used to stage the nuclei (see text and Fig. 1).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2139864&req=5

Figure 5: Telomere distribution at the bouquet stage. Sequential color overlay projections of four nuclei subjected to telomere FISH are shown for the DAPI (DNA, red) and FITC (telomeres, green) images as described in Fig. 3. (A and B) Nuclei identified to be at the “early bouquet” stage (see Results and Discussion) show clustering of telomeres at the nuclear periphery. The nucleolus (n) is remote from the base of the bouquet (bb) in these early bouquet nuclei. (C and D) Two representative zygotene nuclei show colocalization of the base of the bouquet with the nucleolus (n). Gray scale images of knobs are included (insets with arrows) to illustrate the spherical (A) and elongated (D) shapes of these heterochromatic blocks, features used to stage the nuclei (see text and Fig. 1).

Mentions: In striking contrast to the telomere distribution patterns in premeiotic and interphase nuclei, the telomeres of the bouquet stage were clustered at the nuclear periphery. The four bouquet nuclei shown in Fig. 5 illustrate that the nucleus has undergone a substantial reorganization. We found that the earliest bouquet stage nuclei occurred in nuclei identified as late leptotene or prezygotene stage. For example, the nucleus in Fig. 5 A does not yet show signs of prezygotene-specific morphology (elongated knobs), whereas the nucleus in Fig. 5 B, from a similarly sized anther shows elongated knobs and thin chromosome fibers with no signs of synapsis. These early bouquet nuclei were relatively rare and in them the telomere cluster site (bb in Fig. 5 b) was on the opposite side of the nucleus from the nucleolus (n, Fig. 5). At zygotene, the telomere cluster was consistently colocalized with the nucleolus (Fig. 5, C and D) such that the nuclei could be bisected into two distinct hemispheres, one containing the full complement of telomere signals and the nucleolus, and the other devoid of either (Fig. 5, C and D). In all cases, whether early bouquet or zygotene bouquet, the nucleolus took up an eccentric position in the nucleus. Although the bouquet stage can be identified in many species by the parallel arrangement of chromosome ends, this arrangement is not obvious in maize (6, 12, 36). Therefore our results show that telomere FISH signals or nucleolus position can be used to identify the bouquet stage in maize.


Telomeres cluster de novo before the initiation of synapsis: a three-dimensional spatial analysis of telomere positions before and during meiotic prophase.

Bass HW, Marshall WF, Sedat JW, Agard DA, Cande WZ - J. Cell Biol. (1997)

Telomere distribution at the bouquet stage. Sequential color overlay projections of four nuclei subjected to telomere FISH are  shown for the DAPI (DNA, red) and FITC (telomeres, green) images as described in Fig. 3. (A and B) Nuclei identified to be at the  “early bouquet” stage (see Results and Discussion) show clustering of telomeres at the nuclear periphery. The nucleolus (n) is remote  from the base of the bouquet (bb) in these early bouquet nuclei. (C and D) Two representative zygotene nuclei show colocalization of  the base of the bouquet with the nucleolus (n). Gray scale images of knobs are included (insets with arrows) to illustrate the spherical  (A) and elongated (D) shapes of these heterochromatic blocks, features used to stage the nuclei (see text and Fig. 1).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139864&req=5

Figure 5: Telomere distribution at the bouquet stage. Sequential color overlay projections of four nuclei subjected to telomere FISH are shown for the DAPI (DNA, red) and FITC (telomeres, green) images as described in Fig. 3. (A and B) Nuclei identified to be at the “early bouquet” stage (see Results and Discussion) show clustering of telomeres at the nuclear periphery. The nucleolus (n) is remote from the base of the bouquet (bb) in these early bouquet nuclei. (C and D) Two representative zygotene nuclei show colocalization of the base of the bouquet with the nucleolus (n). Gray scale images of knobs are included (insets with arrows) to illustrate the spherical (A) and elongated (D) shapes of these heterochromatic blocks, features used to stage the nuclei (see text and Fig. 1).
Mentions: In striking contrast to the telomere distribution patterns in premeiotic and interphase nuclei, the telomeres of the bouquet stage were clustered at the nuclear periphery. The four bouquet nuclei shown in Fig. 5 illustrate that the nucleus has undergone a substantial reorganization. We found that the earliest bouquet stage nuclei occurred in nuclei identified as late leptotene or prezygotene stage. For example, the nucleus in Fig. 5 A does not yet show signs of prezygotene-specific morphology (elongated knobs), whereas the nucleus in Fig. 5 B, from a similarly sized anther shows elongated knobs and thin chromosome fibers with no signs of synapsis. These early bouquet nuclei were relatively rare and in them the telomere cluster site (bb in Fig. 5 b) was on the opposite side of the nucleus from the nucleolus (n, Fig. 5). At zygotene, the telomere cluster was consistently colocalized with the nucleolus (Fig. 5, C and D) such that the nuclei could be bisected into two distinct hemispheres, one containing the full complement of telomere signals and the nucleolus, and the other devoid of either (Fig. 5, C and D). In all cases, whether early bouquet or zygotene bouquet, the nucleolus took up an eccentric position in the nucleus. Although the bouquet stage can be identified in many species by the parallel arrangement of chromosome ends, this arrangement is not obvious in maize (6, 12, 36). Therefore our results show that telomere FISH signals or nucleolus position can be used to identify the bouquet stage in maize.

Bottom Line: We found that nuclei at the last somatic prophase before meiosis exhibit a nonrandom, polarized chromosome organization resulting in a loose grouping of telomeres.The stage-dependent changes in telomere arrangements are suggestive of specific, active telomere-associated motility processes with meiotic functions.Thus, the formation of the cluster itself is an early event in the nuclear reorganizations associated with meiosis and may reflect a control point in the initiation of synapsis or crossing over.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California at Berkeley 94720, USA.

ABSTRACT
We have analyzed the progressive changes in the spatial distribution of telomeres during meiosis using three-dimensional, high resolution fluorescence microscopy. Fixed meiotic cells of maize (Zea mays L.) were subjected to in situ hybridization under conditions that preserved chromosome structure, allowing identification of stage-dependent changes in telomere arrangements. We found that nuclei at the last somatic prophase before meiosis exhibit a nonrandom, polarized chromosome organization resulting in a loose grouping of telomeres. Quantitative measurements on the spatial arrangements of telomeres revealed that, as cells passed through premeiotic interphase and into leptotene, there was an increase in the frequency of large telomere-to-telomere distances and a decrease in the bias toward peripheral localization of telomeres. By leptotene, there was no obvious evidence of telomere grouping, and the large, singular nucleolus was internally located, nearly concentric with the nucleus. At the end of leptotene, telomeres clustered de novo at the nuclear periphery, coincident with a displacement of the nucleolus to one side. The telomere cluster persisted throughout zygotene and into early pachytene. The nucleolus was adjacent to the cluster at zygotene. At the pachytene stage, telomeres rearranged again by dispersing throughout the nuclear periphery. The stage-dependent changes in telomere arrangements are suggestive of specific, active telomere-associated motility processes with meiotic functions. Thus, the formation of the cluster itself is an early event in the nuclear reorganizations associated with meiosis and may reflect a control point in the initiation of synapsis or crossing over.

Show MeSH