## 4 Discussion
These data indicate that _cep135_ KO cells compensate for the interphasic loss of PCM when entering mitosis. This may mean that even little residual interphase PCM suffices to seed PCM maturation in the mitosis of _cep135_ KO cells. Alternatively, mitotic maturation may be largely independent of the preexisting PCM in interphase. Consistent with this, high-resolution microscopy visualized different forms of PCM organization in interphase and mitosis [1; 32]. It remains to be investigated which molecular determinants, activated at M-phase onset, enable mitotic maturation in WT and cep135 KO cells. These may only be factors regularly involved in mitotic centrosome maturation or additional components that are activated upon loss of CEP135 and subsequent loss of PCM in interphase. Somatic cells may have evolved a surveillance mechanism that scans the functional size of the two MTOCs at the onset of M-phase in somatic cells and ensures balanced spindle pole activities despite unbalanced centrosomes before mitotic onset. Yet, after mitosis, centrosomes without CEP135 decompensate and fall back to structures with diminished PCM, as well as reduced MTOC functions. However, the history of the previous mitotic maturation may help centrosomes to remain, at least in part, functional during the next cell cycle. This may provide an explanation for residual PCM proteins in _cep135_ KO cells and nonpenetrant centrosome splitting. It also explains the disbalance between, most likely, the older (mother) centrosome and the newly assembled centrosome with even lower levels of PCM in interphase. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/cells11071189/s1](https://www.mdpi.com/article/10.3390/cells11071189/s1)]([https://www.mdpi.com/article/10.3390/cells11071189/s1](https://www.mdpi.com/article/10.3390/cells11071189/s1)): **Supplementary Figure S1. KO strategy for _cep135_ in RPE-1 cells. (A) Genome organization of human _CEP135_ with the used guide RNA position indicated by the red arrowhead. (B) Sequencing results of _cep135_ KO alleles of three different cell lines. (C) Immunofluorescence to document the loss of CEP135 in three different cell lines. _cep138_ ko8 was used for all further experiments. Scalebar: 10 \(\upmu\)m or 2 \(\upmu\)m (insets); **Supplementary Figure S2. KO strategy for _sex2 ip_ in RPE-1 cells. (A) Genome organization of human _SSX2 IP_ with the used guide RNA positions indicated by the red arrowheads. (B) Sequencing results of _sex2 ip_ KO alleles of five different cell lines. (C) Immunofluorescence to document the loss of SSX2 IP in five different cell lines. _sex2 ip_ ko2-13 was used for all further experiments. Scalebar: 10 \(\upmu\)m or 2 \(\upmu\)m (insets); **Supplementary Figure S3. KO strategy for _wdr8_ in RPE-1 cells. (A) Genome organization of human WDR8/WRAP73 with the used guide RNA positions indicated by the red arrowheads. (B) Sequencing results of _wdr8_ KO alleles of three different cell lines. (C) Immunofluorescence to document the loss of WDR8 in three different cell lines. _wdr8_ ko308 was used for all further experiments. Scalebar: 10 \(\upmu\)m or 2 \(\upmu\)m (insets); **Supplementary Figure S4. Proliferation analysis of _ssx2 ip_ KO clones, 10\({}^{5}\) cells (3.5 cm\({}^{2}\) dish) were seeded and counted after 24 and 48 h (see Figure 2D); **Supplementary Figure S5. PCM-1 in WT cells, as well as _cep135_, _ssx2 IP_, and _wdr8_ KO cells. (A) Quantification of PCM-1 intensities in WT and KO cells with _cep135_ KO cells bearing a pair of split centrosomes (\"split pair\"). Graphs show mean values (fat colored/black dots) of single experiments and individual data points (transparent dots) with error bars representing the SD from three independent experiments with more than 100 cells quantified in each experiment. The surface plots represent sums (Image) \(z\)-projections) of all images. (B) Representative immunofluorescence images showing the signal of PCM-1 in WT cells, as well as _cep135_, _ssx2 IP_, and _wdr8_ KO cells.