Many stem cells divide asymmetrically in order to balance self-renewal with differentiation. In male germline stem cells ACD is definitely prepared by stereotypical centrosome placing. The centrosome orientation checkpoint (COC) further serves to ensure ACD by avoiding mitosis upon centrosome misorientation. With this study we display that Bazooka (Baz) provides a platform for the correct centrosome orientation and that Baz-centrosome association is the key event that is monitored from the COC. Our work provides a basis for understanding how the correct cell polarity may be identified by the cell to ensure effective ACD. DOI: http://dx.doi.org/10.7554/eLife.04960.001 male germline stem cells (GSCs) like a model to study the checkpoint that coordinates polarization of cells and cell division (Cheng et al. 2008 Inaba et al. 2010 Yuan et al. 2012 male GSCs divide asymmetrically generating one stem cell and one differentiating cell the gonialblast (GB). Asymmetric stem cell division is definitely achieved by stereotypical placing of the mother and child centrosomes in order to orient the spindle perpendicularly to the hub cells the major component of the stem cell market (Yamashita et al. 2003 2007 Stereotypical centrosome behavior that occurs in preparation for asymmetric cell division has been described in additional stem cell systems (Rebollo et al. 2007 Rusan and Peifer 2007 Wang et al. 2009 Conduit and Raff 2010 Januschke et al. 2011 Lu et al. 2012 Salzmann et al. 2014 suggesting the evolutionarily conserved nature of the process. Asymmetric GSC division is definitely further ensured from the centrosome orientation checkpoint (COC) that helps prevent mitotic access in the presence of incorrectly oriented centrosomes (Number 1A) (Cheng et al. 2008 Inaba et al. 2010 Yuan et al. 2012 Upon sensing the centrosome misorientation COC is definitely activated to prevent mitotic access (Number 1A). Therefore the defective COC can be suggested by the NSC 3852 presence of misoriented spindles. We have shown the centrosomal protein Cnn and a polarity kinase Par-1 are crucial component of the COC problems of which leading to high rate of recurrence of spindle misorientation (Inaba et al. 2010 Yuan et al. 2012 Number 1. The apical centrosome associates with the Baz Patch. The Igfbp1 physical basis of right centrosome orientation monitored from the COC remains a mystery. In the case of the spindle assembly checkpoint (SAC) NSC 3852 the lack of microtubule attachment to the kinetochore (or pressure in the kinetochore) is definitely sensed as defective spindle assembly triggering SAC activation to halt mitotic progression (Musacchio and Salmon 2007 In the operation of the COC what is sensed as right or incorrect centrosome orientation to inactivate or activate the COC remains unknown. Here we display that Bazooka (Baz)/Par-3 a well-established polarity protein and a known substrate of Par-1 kinase forms a small subcellular structure that anchors the centrosome right before mitotic access. We provide evidence the association between Baz and the centrosome is the important event that is interpreted to indicate ‘right centrosome NSC 3852 orientation’ by GSCs. We further show that Par-1-dependent phosphorylation of Baz is critical for GSC spindle orientation. Our study provides a platform of the mechanism by which GSC sense right cell polarity. Results Baz forms a subcellular structure between the hub and GSCs that closely associate with the centrosome Baz/Par-3 which is a known physiological substrate of Par-1 contributes to cell polarity and spindle orientation in varied systems (Watts et al. 1996 Benton and St Johnston 2003 Siller and Doe 2009 Because we previously found that Par-1 is definitely a critical component of the COC (Yuan et al. 2012 we examined the part of Baz in the centrosome orientation and/or COC. Baz has been reported to localize in the hub-GSC NSC 3852 interface along with E-cadherin following overexpression in the germline (nos > Baz-GFP) (Leatherman and Dinardo 2010 which was confirmed by using independent UAS-Baz-YFP construct (observe below). However closer inspection using antibody staining and Flytrap Baz-GFP that expresses endogenous levels of Baz [CC01941 (Kelso et al. 2004 Buszczak et al. 2007 revealed that Baz forms foci in the hub-GSC interface (referred to as the ‘Baz patch’ hereafter) instead of entirely colocalizing with E-cadherin (Number 1B C)..