Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi

BUB1

Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_101546

Synonyms

Related Molecules in the Encyclopedia

Historical Background

Bub1 was originally discovered as a gene required for cell cycle arrest during mitosis in response to the microtubule depolymerizing drug benzimidazole in the model organism Saccharomyces cerevisiae (Hoyt et al. 1991). Mutant yeast were unable to arrest and inhibit the budding process at the end of mitosis, a marker for cell cycle progression, hence the name Budding Uninhibited by Benzimidazole 1 (BUB1). Through its capacity to contribute to mitotic arrest, BUB1 functions as an integral component of the spindle assembly checkpoint (SAC), a surveillance mechanism that delays mitotic progression until all kinetochores are properly attached to microtubules, and aligned at the spindle equator in metaphase. Since its original discovery in budding yeast, a SAC function for BUB1 has been verified in all model organisms studied to date (reviewed in (Elowe 2011). Soon after its discovery, hBUB1 was characterized as a Serine/Threonine kinase able to autophosphorylate and constitutively associate with another of the original BUB proteins, BUB3 (Budding Uninhibited by Benzimidazoles 3). It was recognized early on that BUB3 plays an important role in BUB1 recruitment to kinetochores (Roberts et al. 1994; Taylor et al. 1998) which are macromolecular structures that assemble onto centromeres at each mitosis and form both the signaling platform for the SAC as well as the major microtubule binding interface on dividing chromosomes (reviewed (Cheeseman 2014)). The human Bub1 gene maps to chromosome 2 at 2q14, includes 25 exons (NCBI gene ID 699) (Cahill et al. 1999), and was identified by virtue of its homology to budding yeast BUB1 (Cahill et al. 1998). Indeed mutants of this gene were identified in panel of chromosomally instable colorectal cancers. This led to an enormous body of work that aimed to explore mutations in SAC genes in various cancers. While it is now recognized that complete inactivation of the SAC is incompatible with cell survival, this early work was nevertheless influential in that it revived interest in the role of aneuploidy in the development of cancer, and set the pace for much of the more recent work exploring the relationship between mitotic deregulation, chromosome segregation defects, aneuploidy, and cancer (reviewed in (Gordon et al. 2012).

Structural Aspects of BUB1

The BUB1 N-Terminus: A Kinetochore Localization Module

The BUB1 protein has several well-characterized and highly conserved structural motifs (Fig. 1). At the very N-terminus of BUB1 orthologs is the TPR (tetratricopeptide repeat) domain – which consists of a triple tandem repeats of 34 amino acids – that bears strong structural similarity to the TPR domains of the paralog protein BUBR1 (Budding Uninhibited by Benzimidazole Related 1) and MPS1 (MonoPolar Spindle 1), suggesting a common evolutionary ancestor for this domain (Bolanos-Garcia and Blundell 2011; Lee et al. 2012). A short region termed as “loop region” follows the TPR domain and is implicated in BUB3 binding to KNL1 (Kinetochore Null 1, also known as Blinkin or AF15q14 in humans), a kinetochore scaffold protein and a major receptor for SAC signaling molecules (Kiyomitsu et al. 2007). Interestingly, the equivalent loop from BUBR1 cannot substitute for the BUB1 loop in this context (Primorac et al. 2013). The difference between BUB1 and BUBR1 is likely due to their divergent loop sequences which is of functional interest; while the BUB1 loop promotes its recruitment to kinetochores, in BUBR1, this loop may instead be required for interaction with the APC/C (Anaphase Promoting Complex/Cyclosome), a large E3 ubiquitin ligase that is the target of the SAC and the MCC (Mitotic Checkpoint Complex), the principal inhibitory complex of the APC/C (Overlack et al. 2015).
BUB1, Fig. 1

Bub1 structural domains in humans: Bub1 structural domains shown with respective functions and recruitment targets. At N-terminus of Bub1 is a tetratricopeptide repeat (TPR) that interacts with Knl1. The BUB3-binding domain (B3BD)-mediated direct interaction with BUB3. R1LM (BubR1 localization motifs) is needed for direct binding of BubR1 to Bub1 and its kinetochore recruitment. The middle region contains conserved motif1 that is required for SAC and Mad1, Mad2 recruitment, while KEN boxes and ABBA motifs are need for Cdc20 binding and kinetochore recruitment. C-terminal region comprises kinase extension or N-terminal extension domain required for Bub1 activation and a serine/threonine kinase domain whose activity is required for chromosome congression and Sgo1 recruitment in humans. The numbers represent amino acids for each region. “N” and “C” are amino-terminus and carboxy-terminus, respectively

The TPR domain of BUB1 is followed by the BUB3-binding domain (B3BD, also known as the GLEBS (Gle2- Binding Sequence)), a short conserved stretch of 40 amino acids between residues 240 and 280 (hBUB1 numbering) that forms extensive interactions with the β-propeller structures of BUB3 (reviewed in (Bolanos-Garcia and Blundell 2011)). Both the TPR and B3BD are implicated in the kinetochore docking of BUB1, which occurs through direct interaction between BUB1, BUB3, and KNL1 (Taylor et al. 1998; Kiyomitsu et al. 2007). Since the identification of KNL1 (Kiyomitsu et al. 2007), the mechanism of BUB1 binding to kinetochores has been a matter of intense research. KNL1 orthologs contain multiple and often degenerate copies of a short motif known as MELT (for the consensus sequences in hKNL1, Met-Glu-Leu-Thr) (Fig. 2). These motifs are phosphorylated at the Threonine residue by the MPS1 kinase in most species and become direct recognition motifs for BUB3 in complex with BUB1 kinase (London et al. 2012; Shepperd et al. 2012; Primorac et al. 2013). Thus, BUB1 is recruited to kinetochores by upstream phosphorylation of KNL1 by MPS1. Some nematode lineages such as the model organism C. elegans however do not have an MPS1 homologue. Here, the mitotic kinase PLK1 (Polo-Like Kinase 1) is the major kinase of MELT motifs (Espeut et al. 2015). Recent work also suggests that in human cells, PLK1 may cooperate with MPS1 in MELT phosphorylation and BUB1 recruitment (von Schubert et al. 2015). BUB1 binding to kinetochores is further enhanced by interaction with KI1 (Lys-IIe 1) motif of KNL1 (Krenn et al. 2014). Several TΩ (T= Threonine, Ω = Tyrosine/Phenylalanine) motifs, similar to KI1 motif, have been identified that are present in close proximity to MELTs and contribute to hBUB1 kinetochore recruitment (Vleugel et al. 2013). KI motifs are however poorly conserved and may have evolved in higher eukaryotes to allow for more fine-tuned regulation of the BUB1-BUB3 interaction with KNL1. BUB1 recruitment to kinetochores is critical for its function in SAC signaling as it serves to scaffold the kinetochore loading of other checkpoint signaling molecules (Fig. 2), as discussed below.
BUB1, Fig. 2

BUB1 kinetochore recruitment: KNL1 acts as an anchor for BUB1 at kinetochores. At N-terminus, KNL1 binds microtubules (MT), while C-terminus residues 1834–2342 are required for recruitment to kinetochores. KNL1 contains consensus motifs known as MELT motifs. At least 19 MELT motifs have been identified in humans. MPS1 and PLK1 share phosphorylation of these motifs which are read by BUB3 in complex with BUB1. BUB1 also interacts with KI1 of Knl1 which enhances BUB1 binding to kinetochores. Once at kinetochores, BUB1 recruits its downstream targets to kinetochore

The BUB1 Middle Region Contains the SAC Signaling Motifs

BUB1 contains two KEN (Lys-Glu-Asn) boxes (residues 535–537 and 625–627) required for the interaction with and phosphorylation of CDC20 (Cell Division Cycle 20), an activating and specificity-determining co-factor of APC/C (Kang et al. 2008; Jia et al. 2016). Earlier reports identified BUB1 KEN boxes as degradation motifs required for BUB1 destruction by the APC/C (Qi and Yu 2007). However, a later investigation reported a requirement for KEN boxes in hCDC20 binding and phosphorylation in synergy with PLK1, which was proposed to be essential for SAC activation (Jia et al. 2016). Recently, a motif termed as ABBA (Cyclin A, BUBR1, BUB1, and Acm1, also known as the Phe-box, A-box; BUB1 residues 527–532) was shown to contribute to the BUB1-CDC20 interaction (Di Fiore et al. 2015). Deletion of BUB1 residues encompassing this region caused a reduction in CDC20 kinetochore localization (Di Fiore et al. 2015; Vleugel et al. 2015), although a similar role has been proposed for the ABBA motif of the BUB1 paralog BUBR1 (Lischetti et al. 2014). Another important segment in the middle region is the conserved motif1(CD1) (hBUB1 residues 458–476) and is required for SAC function likely through mediating recruitment of MAD (Mitotic Arrest Deficient) 1 and 2 (Klebig et al. 2009).

The BUB1 C-Terminus Includes a Highly Conserved Serine/Threonine Kinase Domain

At the C-terminus, BUB1 has a kinase extension region (amino acids 724–783) required for the activation of BUB1 followed by the kinase domain (amino acids 784–1085), which contributes to chromosome congression and alignment (Kang et al. 2008; Klebig et al. 2009), and potentially the SAC (Tang et al. 2004; Ricke et al. 2011; Ricke et al. 2012; Jia et al. 2016). Two phospho-substrates of BUB1 have been identified so far in addition to its autophosphorylation (See below). BUB1 phosphorylates Histone H2A at S121 which then allows SGO protein binding and recruitment to kinetochores in fission yeast (Kawashima et al. 2010). Similarly mouse and human H2A phosphorylation by BUB1at the equivalent residue has also been reported (Ricke et al. 2012; Liu et al. 2013). A single mutation in Sgo1 (K492A) abolishes the interaction between SGO1 and H2ApT120 (Liu et al. 2013), suggesting that it is the direct site of interaction between these two proteins. On the other hand, CDK1 (cyclin dependent kinase 1) phosphorylates SGO1 at T346, which is required for SGO1 interaction with cohesin, a protein complex needed for sister chromatid cohesion (Liu et al. 2013). The mutation of both sites (K492A and T346A) abolishes SGO1 localization at chromosomes. Hence, both H2AT120 phosphorylation by BUB1 and cohesin binding promote SGO1 recruitment to inner centromeres (Liu et al. 2013). SGO proteins form a complex with PP2A (protein phosphatase 2A) that removes phosphorylation of cohesin subunits to prevent premature sister chromatid separation; thus, BUB1 kinase activity is essential for cohesion protection at centromeres through recruitment of SGO-PP2A complex (Kitajima et al. 2006; Tang et al. 2006). BUB1 phosphorylation of H2AT120 has also been suggested to contribute to SAC functioning through proper localization and activation of the AURORA B kinase at centromeres (Ricke et al. 2012). The second direct substrate of BUB1 kinase activity is CDC20 which contains, at least six sites in its N-terminus potentially phosphorylated by BUB1. Mutation of these sites to alanine causes inefficient APC/C inhibition in vitro and SAC defects in vivo, as measured by early mitotic exit compared control cells (Tang et al. 2004). Recent work suggest that PLK1 may cooperate with BUB1 to phosphorylate these sites, demonstrating yet another potential redundancy in SAC kinase signaling (Jia et al. 2016).

Regulation of BUB1 Kinetochore in Early and Late Mitosis

BUB1 is a stable kinetochore protein in fission yeast and mammalian cells as demonstrated by its relatively slow turnover and exchange at unattached kinetochores compared to other SAC proteins like MAD2, BUBR1, and MPS1 (Howell et al. 2004; Shah et al. 2004; Rischitor et al. 2007). Autophosphorylation has been implicated in restricting hBUB1 turnover at kinetochores (Asghar et al. 2015). Mutation of a single autophosphorylation site to alanine (T589A) increases hBUB1 kinetochore turnover, resulting in an increase in cytoplasmic BUB1 levels and ectopic phosphorylation of its substrate H2AT120, at chromosome arms, and consequently ectopic recruitment of the H2ApT120 binding partner SGO1, resulting in aberrant chromosome congression and sister chromatic cohesion. Artificially stabilizing this BUB1 mutant at kinetochores refocuses H2ApT120 and SGO1 levels back to centromeres (Asghar et al. 2015).

BUB1 begins to accumulate at kinetochores at the start of prophase (Fig. 3), with its levels peaking at prometaphase and gradually diminishing during metaphase when correct attachments between kinetochores and microtubules are established and after which the silencing of the SAC signal occurs. Final loss of BUB1 from the kinetochores occurs during early anaphase (Sharp-Baker and Chen 2001). How BUB1 is removed from kinetochores after chromosome segregation is not well understood, and this area of inquiry has been recently explored. Evidence suggests that BUB1 could be removed from kinetochores by the Dynein motor protein in human cells (Silva et al. 2014). ATP depletion in cells affects Dynein cargo release without affecting Dynein activity; indeed, BUB1 accumulated at spindle poles in ATP depleted human cells (Silva et al. 2014). This was further confirmed when either Dynein or spindly, a recruiter of Dynein at kinetochores, was depleted from cells, which resulted in loss of BUB1 localization to spindle poles, thus confirming that BUB1 is a Dynein cargo (Silva et al. 2014). Another mechanism through which BUB1 may be removed from kinetochores was initially described in budding yeast and implicates PP1 (protein phosphatase 1), a known player in SAC silencing (Vanoosthuyse and Hardwick 2009; Rosenberg et al. 2011). In this organism, BUB1 was stripped from kinetochores in a PP1-dependent manner, through complex formation with the PP1 adaptor subunit Fin1 (Bokros et al. 2016). Cells in which Fin1 protein expression was abrogated displayed abnormal BUB1 signal after anaphase entry, demonstrating the important role of Fin1 and PP1 in BUB1 protein removal from kinetochores and SAC silencing in budding yeast (Bokros et al. 2016). More recently a prominent function during mitotic progression has been demonstrated for the protein phosphatase 2A (PP2A), and in both budding yeast and human cells, it has been suggested that complex interplay between PP1 and PP2A promotes SAC silencing by removing SAC protein including BUB1 from kinetochores (Espert et al. 2014; Nijenhuis et al. 2014).
BUB1, Fig. 3

BUB1 kinetochore localization: Immunofluorescence images are shown in which expression of BUB1 in HeLa is monitored during mitotic progression. Anti-BUB1 and anti-CREST (a centromere marker) antibodies were used to stain mitotic cells. The BUB1 signal can be detected as early as prophase during which BUB1 has a clear punctate signal on kinetochores. As cells traverse mitosis, the signal strength increases and is the strongest during prometaphase. The BUB1 signal begins to diminish in metaphase and is lost completely during anaphase (not shown). DAPI is used to stain the chromosomes and to mark the mitotic stage

Activation of BUB1 Kinase

The crystal structure of the active form of BUB1 kinase domain (Kang et al. 2008) and, more recently, the structure of the active autophosphorylated (pS969) kinase have been reported (Lin et al. 2014). The BUB1 kinase domain deviates from canonical kinase domain found in other kinases such as PKA (protein kinase A) in certain aspects (Lin et al. 2014). For example, the canonical motifs at the catalytic and activation segments are slightly different. The canonical HRD is modified into HGD, the DFG into DLG, and the APE into CVE. Moreover, BUB1, as discussed above, has an extended kinase activation domain also known as an N-terminal extension domain which forms extensive interactions with N- and C-lobe of kinase domain to stabilize it. The mode of activation of BUB1 kinase domains by kinase extension domain is much like cyclins in activating CDKs, and mutations in this kinase extension domain severely attenuate kinase activity of BUB1(Kang et al. 2008). The structural comparison of unphosphorylated and phosphorylated BUB1 (BUB1pS969) showed that there are no major differences between the two structures except in P+1 loop of activation segment. Structural rearrangements in this region after autophosphorylation at S969 act as a molecular switch required for activation of BUB1 kinase (Lin et al. 2014). Autophosphorylation of S969 is needed for kinase activity towards H2A yet it is dispensable for CDC20 phosphorylation which could be due to differences in binding affinity of CDC20 and H2A phosphoresidues with the activation segment of BUB1 (Lin et al. 2014). In addition to localization, the TPR domain of BUB1 was proposed to induce long range activation of C-terminal kinase domain as mutagenesis of this region produced less effective BUB1 kinase activity (Krenn et al. 2012; Ricke et al. 2012). However, later studies using similar methods did not support this mode of activation (Lin et al. 2014; Asghar et al. 2015).

Regulation of SAC by BUB1

BUB1 is a genuine component of the SAC, and its role in SAC has been confirmed and studied in several model organisms including fission yeast, budding yeast, frog, worm, fruit fly, mouse, and humans (Roberts et al. 1994; Taylor and McKeon 1997; Basu et al. 1998; Bernard et al. 1998; Sharp-Baker and Chen 2001; Tang et al. 2004; Encalada et al. 2005). In these studies, depletion or structural mutations in BUB1 cause precocious exit from mitosis. For example, in humans, mutations in TPR domain and BUB3 binding domain caused SAC defects (Klebig et al. 2009). The role of BUB1 kinase activity in SAC function remains controversial. As mentioned above, one target of BUB1 kinase activity for SAC activation is CDC20 (Tang et al. 2004). CDC20 binding to KEN boxes allows for its phosphorylation by hBUB1 and hPLK1 for SAC activation (Jia et al. 2016). Thus, a nonkinase region of hBUB1 may be necessary for kinase activity during SAC activation. BUB1 kinase activity may also promote SAC activity through H2A-T120 phosphorylation and timely AURORA B localization and activation (Ricke et al. 2012). Nevertheless, others have found that kinase-inactivating mutations in the BUB1 catalytic domain do not affect the strength of the SAC (Klebig et al. 2009; Perera and Taylor 2010; Vleugel et al. 2015).

The major role of BUB1 kinase in SAC function may lie in its ability to function as a kinetochore scaffold for downstream proteins (Johnson et al. 2004; Rischitor et al. 2007; Klebig et al. 2009), including BUBR1, MAD1, MAD2, BUB3, SGO, CENP (centromere protein)-E and -F, CDC20 and RZZ (Rod–Zwilich–Zw10) complex (Johnson et al. 2004; Kang et al. 2008; Klebig et al. 2009; Kawashima et al. 2010; Zhang et al. 2015). Distinct structural regions on BUB1 have been implicated in its scaffolding functions. The role of BUB1 in kinetochore recruitment of BUBR1 has been reported in humans (Johnson et al. 2004; Klebig et al. 2009). A central region of BUB1 protein following the TPR domain (residues 266–311), termed as the R1LM (BUBR1 localization motif), is involved in direct pseudo-symmetrical BUBR1 binding and kinetochore recruitment (Overlack et al. 2015; Zhang et al. 2015). In addition to BUBR1 recruitment, a region containing amino acids 430–530 binds and recruits components of RZZ (Rod–Zwilich–ZW10), a complex required for MAD1 and MAD2 protein recruitment and SAC (Zhang et al. 2015). Furthermore, depletion of BUB1 severely reduces ZW10 and Zwilch recruitment to kinetochores, which suggests that BUB1 is required to recruit the entire RZZ complex (Zhang et al. 2015). BUB1 is also required for kinetochore recruitment of MAD1 and MAD2, likely through the CD1 region as mutation of CD1 causes reduction in MAD1 and MAD2 kinetochore localization (Klebig et al. 2009). Furthermore, a conserved RLK (Arg-Leu-Lys) motif of MAD1 is implicated in its interaction with BUB1 and kinetochore recruitment in humans (Kim et al. 2012).

BUB1 and Chromosome Congression

Chromosome congression is the process of chromosome alignment at the spindle equator during a symmetric mitosis. BUB1 is required for this as depletion of BUB1 or structural mutations that reduce BUB1 kinetochore localization cause defects in chromosome alignment (Johnson et al. 2004; Fernius and Hardwick 2007; Logarinho et al. 2008). However, the requirement of kinase activity for chromosome congression is controversial. Expression of BUB1 mutants devoid of kinase activity did not rescue chromosome congression defects caused by BUB1 depletion, demonstrating the importance of BUB1 kinase activity for chromosome congression (Vanoosthuyse et al. 2004; Klebig et al. 2009). However, this remains controversial and other studies in mice and humans did not support the above findings (Perera and Taylor 2010; Baron et al. 2016).

BUB1 and Cancer

Most solid tumors exhibit aneuploidy, a state defined by a number of chromosomes that deviates from the norm for a given species (Weaver and Cleveland 2006). Although aneuploidy may arise due to several contributing factors, in the context of cell division, chromosome cohesion, SAC, and microtubule attachment defects are often observed in aneuploid cells (Gordon et al. 2012). However, the SAC, a signaling cascade particularly essential for cell survival, is rarely fully defective in human tumors, and it has been suggested that an imbalance in SAC signaling in aneuploid tumors contributes to chromosomal instability (CIN), which reflects a higher rate of chromosome gain or loss (Schvartzman et al. 2010). In agreement with this, complete abrogation of SAC causes early development arrest in mouse models and lethality in several tumors; thus, a weakened SAC is detected in many tumors (Weaver and Cleveland 2006; Schvartzman et al. 2010). However, SAC overactivation manifested by abnormal delay in APC/C inhibition can also contribute to CIN due to accumulation of lagging chromosomes and merotelic attachments (Schvartzman et al. 2010). Indeed, BUB1 MAD2 overexpression has been reported in breast cancer patients (Wang et al. 2015), and this overexpression is associated with poor survival and tumor aggressiveness. Reduction of BUB1 and MAD2 expression was sufficient to reduce invasive nature of some tumor cells (Wang et al. 2015). hBub1 is also overexpressed in several human lymphomas, and Bub1 overexpression in mice causes increased chromosome segregation defects due to AURORA B kinase hyperactivation (Ricke et al. 2011).

Although mutations in the SAC genes are not very common (Gordon et al. 2012), one mutation identified in Bub1 results in an amino acid substitution (A130S, in the Bub1 kinetochore localization module) and leads to defects in SAC, chromosome congression and SGO1, BUBR1 and CENP-F recruitment (Klebig et al. 2009). Thus, both structural mutations and abnormal expression of BUB1 might contribute to cancer.

Recent evidence suggests that BUB1 kinase activity plays a role in TGF-β (transforming growth factor-β) signaling in lung and breast cancer cells (Nyati et al. 2015). TGF-β is ubiquitously expressed and involved in many cellular processes related to growth, cell proliferation, and differentiation and its deregulation is associated with cancer (Weiss and Attisano 2013). BUB1 binds to TGFBRs (transforming growth factor beta receptor) at cell membranes and mediates TGF-β signaling through its kinase activity (Nyati et al. 2015). These results show a novel pathway that requires BUB1 kinase activity, which might contribute to cell migration and invasion of tumor cells. In this context, inhibition of BUB1 activity could provide a therapeutic strategy against tumor metastasis. Efforts to date have yielded 2 classes of BUB1 kinase inhibitors: an adenine analog 2OH-BNPP1 and the benzylpyrazole compounds, BAY-320, and BAY-524 (Kang et al. 2008; Baron et al. 2016). Interestingly, 2OH-BNPP1-mediated BUB1 inhibition attenuated TGFβ signaling, suggesting that this may be a viable therapeutic avenue in cancers with hyperactive TGFβ signaling (Nyati et al. 2015). BAY-320 and BAY-524 treatment presented antiproliferative effects in combination with the microtubule-stabilizing and chemotherapeutic drug Paclitaxel (Baron et al. 2016). These studies support further examining the potential use of BUB1 kinase inhibitors for cancer treatment.

Summary

The BUB1 kinase was initially discovered in yeast for its role in mitotic progression and the SAC. Later, it was also identified in other model organisms including fruit fly, frogs, worms, mice, and humans. BUB1 coordinates its activity with other SAC components to delay mitotic progression until correct kinetochore-microtubule attachments are established. Although most studies agree that BUB1 kinase activity is dispensable for its role in the SAC, this remains controversial and the role of the kinase domain may well be context dependent. BUB1’s scaffolding function however is clearly required for the SAC. BUB1 is one of the first SAC proteins to dock at kinetochores to recruit a number of other SAC proteins and mitotic regulators including (but not limited to) BUB3, BUBR1, MAD1, MAD2, SGO, and PP2A. BUB3, BUBR1, MAD, and RZZ are recruited as a result of direct interactions with BUB1(Elowe 2011), while SGO and PP2A are recruited indirectly via BUB1 phosphorylation of H2AT120 or through secondary interactions (e.g., a PP2A pool is recruited through BUBR1 (Kawashima et al. 2010; Suijkerbuijk et al. 2012)). BUB1 phosphorylation of H2AT120 is also required for proper chromosome congression likely, through promoting proper recruitment of AUROR B and SGO proteins. Finally, BUB1 expression is deregulated in several tumors and has a role in tumor progression and is being actively explored as a potential target for therapeutic intervention.

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Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Centre de recherche du CHUM(Notre-Dame) et Institut du Cancer de MontréalQuébecCanada
  2. 2.Axe of Reproduction, Mother and Youth HealthCentre de recherche du Centre Hospitalier Universitaire de QuébecQuébecCanada
  3. 3.The Department of Pediatrics, Faculty of MedicineUniversité LavalQuébec CityCanada