Research article

Non-SMC condensin I complex proteins control chromosome segregation and survival of proliferating cells in the zebrafish neural retina

Sabine Seipold^{* 1} , Florian C Priller^{* 1} , Paul Goldsmith^2,3,4 , William A Harris² , Herwig Baier³ and Salim Abdelilah-Seyfried¹

¹Max Delbrück Center (MDC) for Molecular Medicine, Berlin, Robert-Rössle Str. 10, 13125 Berlin, Germany

²Department of Anatomy, Cambridge University, Cambridge, CB2 3DY, UK

³Department of Physiology, University of California, San Francisco, CA 94158-2722, USA

⁴Department of Neurology, Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne, NE1 4LP, UK

author email corresponding author email* Contributed equally

BMC Developmental Biology 2009, 9:40doi:10.1186/1471-213X-9-40

Published:	8 July 2009

Abstract

Background

The condensation of chromosomes and correct sister chromatid segregation during cell division is an essential feature of all proliferative cells. Structural maintenance of chromosomes (SMC) and non-SMC proteins form the condensin I complex and regulate chromosome condensation and segregation during mitosis. However, due to the lack of appropriate mutants, the function of the condensin I complex during vertebrate development has not been described.

Results

Here, we report the positional cloning and detailed characterization of retinal phenotypes of a zebrafish mutation at the cap-g locus. High resolution live imaging reveals that the progression of mitosis between prometa- to telophase is delayed and that sister chromatid segregation is impaired upon loss of CAP-G. CAP-G associates with chromosomes between prometa- and telophase of the cell cycle. Loss of the interaction partners CAP-H and CAP-D2 causes cytoplasmic mislocalization of CAP-G throughout mitosis. DNA content analysis reveals increased genomic imbalances upon loss of non-SMC condensin I subunits. Within the retina, loss of condensin I function causes increased rates of apoptosis among cells within the proliferative ciliary marginal zone (CMZ) whereas postmitotic retinal cells are viable. Inhibition of p53-mediated apoptosis partially rescues cell numbers in cap-g mutant retinae and allows normal layering of retinal cell types without alleviating their aberrant nuclear sizes.

Conclusion

Our findings indicate that the condensin I complex is particularly important within rapidly amplifying progenitor cell populations to ensure faithful chromosome segregation. In contrast, differentiation of postmitotic retinal cells is not impaired upon polyploidization.