Chinese hamster ovary cell line DXB-11: chromosomal instability and karyotype heterogeneity

Abstract

Background: Chinese hamster ovary cell lines, also known as CHO cells, represent a large family of related, yet quite different, cell lines which are metabolic mutants derived from the original cell line, CHO-ori. Dihydrofolate reductase-deficient DXB-11 cell line, one of the first CHO derivatives, serves as the host cell line for the production of therapeutic proteins. It is generally assumed that DXB-11 is identical to DUKX or CHO-DUK cell lines, but, to our knowledge, DXB-11 karyotype has not been described yet.

Results: Using differential staining approaches (G-, C-banding and Ag-staining), we presented DXB-11 karyotype and revealed that karyotypes of DXB-11 and CHO-DUK cells have a number of differences. Although the number of chromosomes is equal-20 in each cell line-DXB-11 has normal chromosomes of the 1st and 5th pairs as well as an intact chromosome 8. Besides, in DXB-11 line, chromosome der(Z9) includes the material of chromosomes X and 6, whereas in CHO-DUK it results from the translocation of chromosomes 1 and 6. Ag-positive nucleolar organizer regions were revealed in the long arms of chromosome del(4)(q11q12) and both chromosome 5 homologues, as well as in the short arms of chromosomes 8 and add(8)(q11). Only 19 from 112 (16.96%) DXB-11 cells display identical chromosome complement accepted as the main structural variant of karyotype. The karyotype heterogeneity of all the rest of cells (93, 83.04%) occurs due to clonal and nonclonal additional structural rearrangements of chromosomes. Estimation of the frequency of chromosome involvement in these rearrangements allowed us to reveal that chromosomes 9, der(X)t(X;3;4), del(2)(p21p23), del(2)(q11q22) /Z2, der(4) /Z7, add(6)(p11) /Z8 are the most stable, whereas mar2, probably der(10), is the most unstable chromosome. A comparative analysis of our own and literary data on CHO karyotypes allowed to designate conservative chromosomes, both normal and rearranged, that remain unchanged in different CHO cell lines, as well as variable chromosomes that determine the individuality of karyotypes of CHO derivatives.

Conclusion: DXB-11and CHO-DUK cell lines differ in karyotypes. The revealed differential instability of DXB-11 chromosomes is likely not incidental and results in karyotype heterogeneity of cell population.

Keywords: CHO DXB-11 cell line karyotype; CHO chromosomes; Chinese hamster ovary cells; Chromosomal instability; Karyotype heterogeneity.

Fig. 1

G-banded karyotype of Chinese hamster ovary DXB-11 cell line (main SVK). 20,–X,der(X)(Xpter → Xq11::3p13 → 3p21::4p11 → 4pter),del(2)(pter → p23::p21 → qter),del(2)(pter → q11::q22 → qter),inv(3)(pter → p26::q11 → p26::q11 → qter),der(3)(?8q::3p13 → 3q37::?),del(4)(pter → q11::q12 → qter),der(4)(3pter → 3p21::4p11 → 4q1?5::4q?::4q112 → 4qter),add(6)(?::p11 → qter),der(6)(Xq?::6q13 → 6p11::?::6q15 → 6qter),–7,–7,add(8)(pter → q11::?),–9,–10,–10,+4mar. The arrows indicate structurally rearranged chromosomes

Fig. 2

Identification of the 2nd, 3rd and 4th chromosome pairs. a Deletions of the short arm of the first chromosome 2 homologue, del(2)(p21p23), and of the long arm of the second chromosome 2 homologue, del(2)(q11q22). b Chromosome inv(3)(pter → p26::q11 → p26::q11 → qter) and distribution of the second chromosome 3 material between der(3), der(X), and der(4). c Chromosome del(4)(pter → q11::q12 → qter) and distribution of the second chromosome 4 material between der(X) and der(4). The arrows indicate structurally rearranged chromosomes. Deleted and corresponding chromosome regions marked by lines

Fig. 3

a C-banded karyotype of Chinese hamster ovary DXB-11 cell line (main SVK). The arrows indicate structurally rearranged chromosomes. b AgNOR staining pattern of DXB-11 chromosomes (metaphase spread). The arrows indicate Ag-positive chromosomes

Fig. 4

Differential instability of DXB-11 chromosomes. Horizontal axis—chromosomes of karyotype, vertical axis—frequency of chromosome involvement in ASR, %. Vertical bars are the errors of percentage

Fig. 5

The most frequent clonal ASR. a Derivative variants of mar2 either with additional material on the long arm (mar2⁴) or with deletions of the long arm (shown by lines). b G- and C- banded chromosomes 8, add(8)(q11)¹ and mar2². c Deletion of the long arm of chromosome add(8)(q11), add(8)(q11)² and mar2⁴. d der(1)(1pter → 1q42::4q26 → 4qter) and der(4)(4pter → 4q11::4q12 → 4q26::1q42 → 1qter) resulting from balanced translocation of chromosomes 1 and del(4)(q11q12), G- banding and Ag-staining. e der(5)(5pter → 5q28::8q25 → 8qter) and der(8)(8pter → 8q25::5q28 → 5qter) resulting from balanced translocation of chromosomes 5 and 8, and add(5)(?::p14 → qter) and deletion of the short arm of mar1, mar1¹, G- banding and Ag-staining. f Chromosomes 5 and del(5)(p11), G- banding and Ag-staining. g del(8)(:p13 → pter) and derivative chromosome mar4¹, G- banding and Ag-staining. h der(3)¹ resulting from interstitial deletion of the long arm of chromosome der(3). i, j der(4)(?::4p33 → 4q11::4q12 → 4qter) and der(5)(?::5p12 → 5qter) resulting from the translocation of the long arm of mar3 to chromosomes del(4) (i) or 5 (j), and mar3¹. Arrows indicate ASR of normal chromosomes of the main SVK. Double arrows indicate ASR of structurally rearranged chromosomes of the main SVK

Fig. 6

A schematic representation of chromosome loci involved in structural rearrangements in the main SVK (arrows), in clonal ASR (arrowheads) and in nonclonal ASR (circles) in DXB-11 cell line. In frame: images of the marker chromosomes of the main SVK. Idiograms of G-banding patterns for normal chromosomes of Cricetulus griseus [26] are used. In dotted frames: chromosomes 7 and 10 whose identification is impossible due to their complex rearrangements