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Figure 3: Biochemically distinct

condensin complexes with

interchangeable subunits control

chromosome structure

throughout C. elegans

development. a, Each condensin

complex contains a pair of SMC

proteins (Structural Maintenance of

Chromosomes) and three non-SMC

subunits. SMC proteins have

nucleotide binding domains at

their globular N- and C-termini,

which are linked by two long coiled

coil domains separated by a hinge

region. The dosage compensation

condensin complex (condensin IDC)

specifically changes the molecular

topology of interphase X

chromosomes in XX embryos to

repress gene expression by half. b,

An XX embryo co-stained with a

DNA dye and the DCC-specific

subunit DPY-27 shows X-specific

localization of the DCC. Condensin

I and II perform independent roles

in the structure and segregation of

mitotic and meiotic chromosomes,

with condensin II being the primary

regulator of chromosome

compaction and resolution (see

also h). Both condensin I and II

affect the number and distribution

of double strand breaks in meiosis,

and thereby the number and

position of crossovers between

homologous chromosomes, by

controlling the higher-order

chromosome structure. c,

Confocal images show that

mutations disrupting condensin I

and II subunits cause an additive

extension of chromosome axes.

Meiotic X-chromosome axes from

paired and synapsed homologs in

pachytene nuclei of wild-type and

condensin-mutant gonads were

stained with antibodies to the axial

protein HTP-3, traced in 3

dimensions, and computationally

straightened. Axial length is shown.

Condensin II co-localizes with

centromere proteins and mediates

faithful chromosome segregation.

d, Two-celled, wild-type embryo

stained with DNA dye (blue) and

antibodies to tubulin (green) and

the centromere-specific histone

HCP-3 (red). The cell on the left is

in metaphase of mitosis. e,

One-celled, wild-type embryo in

metaphase stained with DNA dye

(blue) and antibodies to tubulin

(green) and the condensin II

subunit SMC-4 (red). f, Enlargement

of mitotic chromosomes in

metaphase co-stained with DNA

dye (blue) and antibodies to SMC-4

(green) and HCP-3 (red). The

merged image (bottom) shows the

colocalization of centromere

proteins and condensin II on the

holocentric nematode

chromosomes. DNA-stained

wild-type (g) and smc-4(-) (h)

embryos after segregation of

homologs (polar body, green

arrow) and sister chromatids (polar

body, white arrow) and migration

and fusion of the sperm (s) and

oocyte (o) pronuclei. In smc-4(-)

embryos the oocyte pronucleus

remains connected to the sister

chromatids in the polar body,

demonstrating improper

chromosome segregation in

meiosis. The dosage

compensation subunit MIX-1 is

shared with condensin II and

behaves similarly to SMC-4 in

mitosis.

Figure 3: Biochemically distinct condensin complexes with interchangeable subunits control chromosome structure throughout C. elegans development. a, Each condensin complex

contains a pair of SMC proteins (Structural Maintenance of Chromosomes) and three non-SMC subunits. SMC proteins have nucleotide binding domains at their globular N- and C-termini, which are

linked by two long coiled coil domains separated by a hinge region. The dosage compensation condensin complex (condensin IDC) specifically changes the molecular topology of interphase X

chromosomes in XX embryos to repress gene expression by half. b, An XX embryo co-stained with a DNA dye and the DCC-specific subunit DPY-27 shows X-specific localization of the DCC.

Condensin I and II perform independent roles in the structure and segregation of mitotic and meiotic chromosomes, with condensin II being the primary regulator of chromosome compaction and

resolution (see also h). Both condensin I and II affect the number and distribution of double strand breaks in meiosis, and thereby the number and position of crossovers between homologous

chromosomes, by controlling the higher-order chromosome structure. c, Confocal images show that mutations disrupting condensin I and II subunits cause an additive extension of chromosome

axes. Meiotic X-chromosome axes from paired and synapsed homologs in pachytene nuclei of wild-type and condensin-mutant gonads were stained with antibodies to the axial protein HTP-3, traced

in 3 dimensions, and computationally straightened. Axial length is shown.

Condensin II co-localizes with centromere proteins and mediates faithful chromosome segregation. d, Two-celled, wild-type embryo stained with DNA dye (blue) and antibodies to tubulin (green) and

the centromere-specific histone HCP-3 (red). The cell on the left is in metaphase of mitosis. e, One-celled, wild-type embryo in metaphase stained with DNA dye (blue) and antibodies to tubulin

(green) and the condensin II subunit SMC-4 (red). f, Enlargement of mitotic chromosomes in metaphase co-stained with DNA dye (blue) and antibodies to SMC-4 (green) and HCP-3 (red). The merged

image (bottom) shows the colocalization of centromere proteins and condensin II on the holocentric nematode chromosomes. DNA-stained wild-type (g) and smc-4(-) (h) embryos after segregation of

homologs (polar body, green arrow) and sister chromatids (polar body, white arrow) and migration and fusion of the sperm (s) and oocyte (o) pronuclei. In smc-4(-) embryos the oocyte pronucleus

remains connected to the sister chromatids in the polar body, demonstrating improper chromosome segregation in meiosis. The dosage compensation subunit MIX-1 is shared with condensin II and

behaves similarly to SMC-4 in mitosis.