Centromere Protein B Null Mice are Mitotically and Meiotically Normal but Have Lower Body and Testis Weights

Abstract

CENP-B is a constitutive centromere DNA-binding protein that is conserved in a number of mammalian species and in yeast. Despite this conservation, earlier cytological and indirect experimental studies have provided conflicting evidence concerning the role of this protein in mitosis. The requirement of this protein in meiosis has also not previously been described. To resolve these uncertainties, we used targeted disruption of the Cenpb gene in mouse to study the functional significance of this protein in mitosis and meiosis. Male and female Cenpb null mice have normal body weights at birth and at weaning, but these subsequently lag behind those of the heterozygous and wild-type animals. The weight and sperm content of the testes of Cenpb null mice are also significantly decreased. Otherwise, the animals appear developmentally and reproductively normal. Cytogenetic fluorescence-activated cell sorting and histological analyses of somatic and germline tissues revealed no abnormality. These results indicate that Cenpb is not essential for mitosis or meiosis, although the observed weight reduction raises the possibility that Cenpb deficiency may subtly affect some aspects of centromere assembly and function, and result in reduced rate of cell cycle progression, efficiency of microtubule capture, and/or chromosome movement. A model for a functional redundancy of this protein is presented.

Oligozoospermia with normal fertility in male mice lacking the androgen receptor in testis peritubular myoid cells

“…This finding is not surprising as it was reported that an impact on fertility should have an estimated sperm count reduction to 10% or less (22). Furthermore, previous reports have demonstrated several animal models with reduced sperm count but normal fertility (22)(23)(24)(25)(26). ADP-ribosylation factor-like 4 (Arl4) is a GTP-binding protein that shuttles between the nucleus and intracellular organelles depending on GTP͞GDP-binding status.…”

“…In addition, FSH␤ has been reported to play a role in spermatogenesis and mice lacking FSH␤ are also fertile despite having a reduced testis size and epididymal sperm count (25,26). Furthermore, centromere protein B is a DNA-binding protein required for meiosis, and its deletion caused a reduction in testis weight by 30% and a 40% reduction in sperm count without a reduction in fertility (24). Finally, mice with disrupted protein inhibitor of activated STAT splice variant also show a similar phenotype with absolute testicular weight decrease of 23% and sperm count decrease of 19% (22).…”

Centromere Proteins Cenpa, Cenpb, and Bub3 Interact with Poly(ADP-ribose) Polymerase-1 Protein and Are Poly(ADP-ribosyl)ated

“…CENP-E, CENP-F, INCENP, survivin, MCAK, ZWINT-1, ZW10, MAD-1, MAD-2, BUB1, BUBR1, and BUB3) associate with the centromere during specific stages of the cell cycle. Constitutive proteins CENP-A, CENP-C, and CENP-H are essential for correct kinetochore assembly and function as evidenced by a lethal phenotype in gene knockout and antibody/RNA inhibition studies in mouse, worm, and chicken DT40 cells (13)(14)(15)(16)(17)(18)(19)(20)(21), whereas CENP-B appears to be functionally redundant for centromere activity (22)(23)(24). Numerous gene knockout and inhibition studies have demonstrated that many of the transient proteins have essential roles in normal mitotic functions, such as INCENP, survivin, CENP-E, BUB3, and MAD2 (25)(26)(27)(28)(29)(30).…”

“…For the preparation of nuclear protein extracts, 10 7 cells were harvested and lysed in ice-cold lysis buffer as previously described (24).…”

The Centromere: Epigenetic Control of Chromosome Segregation during Mitosis

“…Human centromeric DNA contains the 17-bp "CENP-B box," which directly recruits the centromere protein CENP-B (Masumoto et al 1989). CENP-B knockout mice are for the most part phenotypically normal (Hudson et al 1998;Kapoor et al 1998;Perez-Castro et al 1998) and functional neocentromeres lack CENP-B (Saffery et al 2000). Moreover, CENP-B is absent from the human Y chromosome (Earnshaw et al 1987) and no CENP-B functional homologs have been identified in Xenopus, zebrafish, C. elegans, or Drosophila to date.…”