Cell-type specific proximity of centromeric domains of one homologue each of chromosomes 2 and 11 in nuclei of cerebellar Purkinje neurons

Abstract

In Purkinje neurons of the mouse cerebellum, the centromeres of several chromosomes are placed in close proximity to form a distinct pattern of clusters and exhibit reproducible spatial redistributions during development. In granule neurons, an adjacent cell type in the cerebellum, the pattern, size, and number of centromeric aggregations are different from those of Purkinje neurons. The present work was undertaken to test the hypothesis that the same chromosomes form part of one aggregate in a cell-type-specific manner. Fluorescence in situ hybridization (FISH) with chromosome-specific paracentromeric probes was used to identify centromeric regions of individual chromosomes in cerebellar Purkinje and granule neurons of the adult mouse. When pairs of centromeric probes were used in two-color FISH, one homologue each of chromosomes 2 and 11 were routinely found close to each other in Purkinje neurons but not in granule neurons. This finding of specific proximity was limited to the pair 2 and 11, out of the ten chromosome pairs that were randomly selected and studied. Our results indicate that, in adult Purkinje neurons, a cell-type-specific spatial proximity is present between centromeric domains of one homologue each of chromosomes 2 and 11.

Trend towards varying combinatorial centromere association in morphologically identical clusters in Purkinje neurons

“…Previous work has shown that centromeres of chromosomes 2 and 11 were detected in close proximity in Purkinje neurons [11]. The results of the present work show that the additional chromosomes that contribute their centromeres to the same cluster that contains centromeres of chromosomes 2 and 11 vary.…”

“…2). We have previously reported the routine clustering of chromosome pairs 2 and 11 in Purkinje neurons [11]. In contrast to this, pairs 2&3, 2&8 and 6&8 routinely did not show clustering of centromeres.…”

“…Centromeric repeat homology is also found in small RNAs in RNA interference (RNAi) effecter complex RITZ [15]. In these contexts, the clustered centromeric heterochromatin in Purkinje neurons [8,11,16] may have important functional roles. The size and number of centromeric clusters in adult Purkinje neurons remained almost the same with less variability [8] leading to the hypothesis that it is the same chromosomes that always contribute their centromeric domains to a given cluster.…”

“…Image galleries were used to generate 3D volume of the nuclei and the relative spatial positions of the signals were measured. The sizes of centromere clusters were measured and their diameters were used as the maximum possible distance at which the centromeres can be present, but still be part of a centromere cluster [11]. Signals that were present at the central chromocenter of Purkinje neuron nuclei were categorized as part of a centromere cluster if the distance between signals was ≤ 3.5 μm and those outside the central chromocenter were categorized as part of a centromere cluster if the distance between the signals was ≤ 1.54 μm.…”

“…Second, if they are part of two separate clusters, they never cluster. Our recent work has shown routine clustering of centromeres of one homologue each of chromosomes 2 and 11 in Purkinje neurons [11]. To test whether centromere clustering between other chromosomes in Purkinje neurons has chromosome-chromosome specificity, we carried out FISH using chromosome-specific para-centromeric sequences from randomly picked pairs of chromosomes.…”