Dosage Effects of Cohesin Regulatory Factor PDS5 on Mammalian Development: Implications for Cohesinopathies

Cornelia de Lange syndrome (CdLS), a disorder caused by mutations in cohesion proteins, is characterized by multisystem developmental abnormalities. PDS5, a cohesion protein, is important for proper chromosome segregation in lower organisms and has two homologues in vertebrates (PDS5A and PDS5B). Pds5B mutant mice have developmental abnormalities resembling CdLS; however the role of Pds5A in mammals and the association of PDS5 proteins with CdLS are unknown. To delineate genetic interactions between Pds5A and Pds5B and explore mechanisms underlying phenotypic variability, we generated Pds5A-deficient mice. Curiously, these mice exhibit multiple abnormalities that were previously observed in Pds5B-deficient mice, including cleft palate, skeletal patterning defects, growth retardation, congenital heart defects and delayed migration of enteric neuron precursors. They also frequently display renal agenesis, an abnormality not observed in Pds5B−/− mice. While Pds5A−/− and Pds5B−/− mice die at birth, embryos harboring 3 mutant Pds5 alleles die between E11.5 and E12.5 most likely of heart failure, indicating that total Pds5 gene dosage is critical for normal development. In addition, characterization of these compound homozygous-heterozygous mice revealed a severe abnormality in lens formation that does not occur in either Pds5A−/− or Pds5B−/− mice. We further identified a functional missense mutation (R1292Q) in the PDS5B DNA-binding domain in a familial case of CdLS, in which affected individuals also develop megacolon. This study shows that PDS5A and PDS5B functions other than those involving chromosomal dynamics are important for normal development, highlights the sensitivity of key developmental processes on PDS5 signaling, and provides mechanistic insights into how PDS5 mutations may lead to CdLS

Histone H1 Subtypes Differentially Modulate Chromatin Condensation without Preventing ATP-Dependent Remodeling by SWI/SNF or NURF

Although ubiquitously present in chromatin, the function of the linker histone subtypes is partly unknown and contradictory studies on their properties have been published. To explore whether the various H1 subtypes have a differential role in the organization and dynamics of chromatin we have incorporated all of the somatic human H1 subtypes into minichromosomes and compared their influence on nucleosome spacing, chromatin compaction and ATP-dependent remodeling. H1 subtypes exhibit different affinities for chromatin and different abilities to promote chromatin condensation, as studied with the Atomic Force Microscope. According to this criterion, H1 subtypes can be classified as weak condensers (H1.1 and H1.2), intermediate condensers (H1.3) and strong condensers (H1.0, H1.4, H1.5 and H1x). The variable C-terminal domain is required for nucleosome spacing by H1.4 and is likely responsible for the chromatin condensation properties of the various subtypes, as shown using chimeras between H1.4 and H1.2. In contrast to previous reports with isolated nucleosomes or linear nucleosomal arrays, linker histones at a ratio of one per nucleosome do not preclude remodeling of minichromosomes by yeast SWI/SNF or Drosophila NURF. We hypothesize that the linker histone subtypes are differential organizers of chromatin, rather than general repressors

DNA-condensing and chromatin-condensing properties of rat testes hla and hit compared to those of rat-liver hlbdec - hlt is a poor condenser of chromatin

Histones H1a and H1t are two major linker histone variants present at the pachytene interval of mammalian spermatogenesis. The DNA- and chromatin-condensing properties of these two variants isolated from rat testes were studied and compared with those from rat liver. For this purpose, the histone H1 subtypes were purified from the respective tissues using bath acid and salt extraction procedures, Circular dichroism studies revealed that acid exposure during isolation affects the alpha-helical structure of both the globular domain (in the presence of 1 M NaCl) and the C-terminal lambda-tail (in the presence of 60% trifluoroethanol). The condensation of rat oligonucleosomal DNA, as measured by circular dichroism spectroscopy, by the salt-extracted histone H1 was at least 10 times more efficient than condensation by the acid-extracted histone H1. A site size of 16-20 base pairs was calculated for the salt-extracted histone H1. Among the different histone H1 subtypes, somatic histone H1bdec had the highest DNA-condensing property, followed by histone H1a and histone H1t. All the salt-extracted histones condensed rat oligonucleosomal DNA more efficiently than linear pBR-322 DNA, Histones H1bdec and H1a condensed histone H1-depleted chromatin, prepared from rat liver nuclei, with relatively equal efficiency. On the other hand, there was no condensation of histone H1-depleted chromatin with the testes specific histone H1t. A comparison of the amino acid sequences of histone H1d (rat) and histone H1t (rat) revealed several interesting differences in the occurrence of DNA-binding motifs at the C-terminus. A striking observation is the presence of a direct repeat of an octapeptide motif K(A)T(S)PKKA(S)K(T)K(A) in histone H1d that is absent in histone H1t

Condensation of DNA and chromatin by an SPKK-containing octapeptide repeat motif present in the C-terminus of histone H1

Several DNA binding motifs have been described in the C-terminus of histone H1 (Churchill & Travers, 1991), of these the S/TPKK repeat (Suzuki, 1989) often occurs as a part of an octapeptide repeat of the type XTPKKXKK. We have studied in detail the DNA and chromatin condensing properties of a consensus octapeptide KSPKKAKK (8 mer) present in many histone H1 subtypes and its imperfect repeat ATPKKSTKKTPKKAKK (16 mer TPKK) as it occurs in the C-tenminus of rat histone Hid. The 16 mer TPKK peptide containing two S/TPKK motifs was able to condense both rat oligonucleosomal (2-5 kbp) DNA and histone Hi-depleted chromatin as revealed by circular dichroism spectroscopy. The 8 mer peptide, however, was unable to condense either the DNA or the histone Hi-depleted chromatin. Both the 8 mer peptide and the 16 mer TPKK peptide displaced distamycin A from the drug-DNA complex, although with different efficiency, indicating that while these two peptides could bind DNA, only the 16 mer (TPKK) peptide could brine about condensation of DNA and histone Hi-depleted chromatin. A mutant 16 mer (TAKK) peptide wherein two proline residues are replaced by alanine, was ineffective in bringing about condensation of both DNA and histone Hi-depleted chromatin. These results suggest that the two p-turn structures present in the 16 mer (TPKK) peptide could be important in facilitating binding to different regions of duplex DNA thereby bringing about close packing and condensation. The condensation property of the 16 mer (TPKK) peptide was very similar to that of histone H1 in terms of (a) its preference for AT rich DNA, (b) cooperativity of condensation, and (c) salt dependence of condensation. The 16 mer (TPKK) peptide, but not the 8 mer peptide or the 16 mer (TAKK) peptide, could form complexes with a polynucleosomal 5S DNA core resulting in retarded mobility similar to the complexes formed with histone H1 on agarose gel electrophoresis

Expression of rat histone H1d in Escherichia coli and its purification

Histone H1 is involved in the folding of linear polynucleosomal filament into a 30-nm fiber. In an effort to understand the role of different domains of histone H1 in chromatin folding, we have now expressed rat histone H1d in Escherichia coli using pTrc99A expression vector by providing a 6-His tag at the C-terminus to facilitate its purification, The expressed protein histone H1d was purified from the soluble extract of E. coli by employing Ni2+ NTA-agarose and heparin-agarose chromatography. The recombinant histone H1d was shown to be authentic by its N-terminal amino acid analysis, its secondary structural characteristics, and its ability to (a) condense DNA and (b) bind specifically to synthetic four-way junction DN

Testis-specific histone (H1t) is not phosphorylated and has a weak interaction with chromatin

Soluble chromatin was prepared from rat testes after a brief micrococcal nuclease digestion. After adsorption onto hydroxylapatite at low ionic strength, the histone Hl subtypes were eluted with a shallow salt gradient of 0.3 M NaCl to 0.7 M NaCl. Histone Hlt was eluted at 0.4 MNaCl, while histones H1a and Hlc were eluted at 0.43 M NaCl and 0.45 M respectively. The extreme divergence of the amino acid sequence of the C-terminal half of histone Hlt, the major DNA binding domain of histone Hl, from that of the somatic consensus sequence may contribute to the weaker interaction of histone Hlt with the rat testis chromatin. Further, histone Hlt was not phosphorylated in vivo in contrast to histone Hla and Hlc, as is evident from the observation that histone Hlt lacks the SPKK motif recognized by the CDC-2kinase or the RR/KXS motif recognized by protein kinase A

A multi-domain protein for beta1 integrin-targeted DNA delivery.

The development of effective receptor-targeted nonviral vectors for use in vivo is complicated by a number of technical problems. One of these is the low efficiency o