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Lindsay J Frehlick

Publications and source records attributed to Lindsay J Frehlick.

8 recordsLinked to original sources
PubMed2007

New insights into the nucleophosmin/nucleoplasmin family of nuclear chaperones.

Basic proteins and nucleic acids are assembled into complexes in a reaction that must be facilitated by nuclear chaperones in order to prevent protein aggregation and formation of non-specific nucleoprotein complexes. The nucleophosmin/nucleoplasmin (NPM) family of chaperones [NPM1 (nucleophosmin), NPM2 (nucleoplasmin) and NPM3] have diverse functions in the cell and are ubiquitously represented throughout the animal kingdom. The importance of this family in cellular processes such as chromatin remodeling, genome stability, ribosome biogenesis, DNA duplication and transcriptional regulation has led to the rapid growth of information available on their structure and function. The present review covers different aspects related to the structure, evolution and function of the NPM family. Emphasis is placed on the long-term evolutionary mechanisms leading to the functional diversification of the family members, their role as chaperones (particularly as it pertains to their ability to aid in the reprogramming of chromatin), and the importance of NPM2 as an essential component of the amphibian chromatin remodeling machinery during fertilization and early embryonic development.

Animals↗
PubMed2006

A unique vertebrate histone H1-related protamine-like protein results in an unusual sperm chromatin organization.

Protamine-like proteins constitute a group of sperm nuclear basic proteins that have been shown to be related to somatic linker histones (histone H1 family). Like protamines, they usually replace the chromatin somatic histone complement during spermiogenesis; hence their name. Several of these proteins have been characterized to date in invertebrate organisms, but information about their occurrence and characterization in vertebrates is still lacking. In this sense, the genus Mullus is unique, as it is the only known vertebrate that has its sperm chromatin organized by virtually only protamine-like proteins. We show that the sperm chromatin of this organism is organized by two type I protamine-like proteins (PL-I), and we characterize the major protamine-like component of the fish Mullus surmuletus (striped red mullet). The native chromatin structure resulting from the association of these proteins with DNA was studied by micrococcal nuclease digestion as well as electron microscopy and X-ray diffraction. It is shown that the PL-I proteins organize chromatin in parallel DNA bundles of different thickness in a quite distinct arrangement that is reminiscent of the chromatin organization of those organisms that contain protamines (but not histones) in their sperm.

Amino Acid Sequence↗
PubMed2006

Long-term evolution and functional diversification in the members of the nucleophosmin/nucleoplasmin family of nuclear chaperones.

The proper assembly of basic proteins with nucleic acids is a reaction that must be facilitated to prevent protein aggregation and formation of nonspecific nucleoprotein complexes. The proteins that mediate this orderly protein assembly are generally termed molecular (or nuclear) chaperones. The nucleophosmin/nucleoplasmin (NPM) family of molecular chaperones encompasses members ubiquitously expressed in many somatic tissues (NPM1 and -3) or specific to oocytes and eggs (NPM2). The study of this family of molecular chaperones has experienced a renewed interest in the past few years. However, there is a lack of information regarding the molecular evolution of these proteins. This work represents the first attempt to characterize the long-term evolution followed by the members of this family. Our analysis shows that there is extensive silent divergence at the nucleotide level suggesting that this family has been subject to strong purifying selection at the protein level. In contrast to NPM1 and NPM-like proteins in invertebrates, NPM2 and NPM3 have a polyphyletic origin. Furthermore, the presence of selection for high frequencies of acidic residues as well as the existence of higher levels of codon bias was detected at the C-terminal ends, which can be ascribed to the critical role played by these residues in constituting the acidic tracts and to the preferred codon usage for phosphorylatable amino acids at these regions.

Animals↗
PubMed2006

The characterization of amphibian nucleoplasmins yields new insight into their role in sperm chromatin remodeling.

BACKGROUND: Nucleoplasmin is a nuclear chaperone protein that has been shown to participate in the remodeling of sperm chromatin immediately after fertilization by displacing highly specialized sperm nuclear basic proteins (SNBPs), such as protamine (P type) and protamine-like (PL type) proteins, from the sperm chromatin and by the transfer of histone H2A-H2B. The presence of SNBPs of the histone type (H type) in some organisms (very similar to the histones found in somatic tissues) raises uncertainty about the need for a nucleoplasmin-mediated removal process in such cases and poses a very interesting question regarding the appearance and further differentiation of the sperm chromatin remodeling function of nucleoplasmin and the implicit relationship with SNBP diversity The amphibians represent an unique opportunity to address this issue as they contain genera with SNBPs representative of each of the three main types: Rana (H type); Xenopus (PL type) and Bufo (P type). RESULTS: In this work, the presence of nucleoplasmin in oocyte extracts from these three organisms has been assessed using Western Blotting. We have used mass spectrometry and cloning techniques to characterize the full-length cDNA sequences of Rana catesbeiana and Bufo marinus nucleoplasmin. Northern dot blot analysis shows that nucleoplasmin is mainly transcribed in the egg of the former species. Phylogenetic analysis of nucleoplasmin family members from various metazoans suggests that amphibian nucleoplasmins group closely with mammalian NPM2 proteins. CONCLUSION: We have shown that these organisms, in striking contrast to their SNBPs, all contain nucleoplasmins with very similar primary structures. This result has important implications as it suggests that nucleoplasmin's role in chromatin assembly during early zygote development could have been complemented by the acquisition of a new function of non-specifically removing SNBPs in sperm chromatin remodeling. This acquired function would have been strongly determined by the constraints imposed by the appearance and differentiation of SNBPs in the sperm.

Animals↗
PubMed2006

Sperm nuclear basic proteins of two closely related species of Scorpaeniform fish (Sebastes maliger, Sebastolobus sp.) with different sexual reproduction and the evolution of fish protamines.

In this paper, we present a review of sperm nuclear basic proteins (SNBPs) in teleost fish. The distribution of the three basic groups of SNBPs [histone (H)-type, protamine-like (PL)-type and protamine (P)-type], their evolution and possible relation to the mode of fertilization are described. In this regard, we have characterized the SNBPs from two closely related species of Scorpaeniform fish: internally fertilizing Sebastes maliger and externally fertilizing Sebastolobus sp., both in the family Scorpaenidae. Despite the different reproductive behavior of these two closely related rockfish species, in both instances the SNBP consists of protamines. However, there is a significant increase in the arginine content of the protamine in the internally fertilizing rockfish. The relevance of this observation is discussed within the context of the P-type SNBP in teleosts. The rapid evolution of teleost protamines, including those in rockfish, has also allowed us to obtain a molecular phylogeny for this group of bony fish that is almost indistinguishable from that currently available from the use of conventional anatomical/paleontological markers.

Amino Acid Sequence↗
PubMed2005

Protamines in the internally fertilizing neobatrachian frog Eleutherodactylus coqui.

The internally fertilizing primitive frog Ascaphus truei (family Ascaphidae) from the Pacific Northwest is the only frog with an intromittent organ. The more advanced neobatrachian frog Eleutherodactylus coqui (family Leptodactylidae) from Puerto Rico has secondarily acquired internal fertilization but mates by cloacal apposition. Nonetheless, both frogs have introsperm with an elongated head containing highly condensed chromatin. Characterization of sperm nuclear basic proteins (SNBPs) in E. coqui by acid-urea polyacrylamide gel electrophoresis indicates that, as in A. truei, testes from a single animal contain several protamines. Amino acid analysis indicates a composition for the most rapidly moving protamine of each species as follows: in E. coqui, ARG (35.6 mol %) + LYS (3.8 mol %) + HIS (7.6 mol %) = 47 mol % total basic residues and in A. truei, ARG (42.1 mol %) + LYS (11.1 mol %) = 53.2 mol % total basic residues. Transmission electron microscopy shows that E. coqui introsperm, like those in A. truei, are elongate with highly condensed chromatin. However, E. coqui introsperm lacks an axial perforatorium that extends into an endonuclear canal. These morphological features are plesiomorphic (primitive) and shared by A. truei with urodeles and basal amniotes (Jamieson et al. (1993) Herpetologica 49:52-65). In E. coqui introsperm, the nucleoprotein complex has a cross-sectional axis of 420 + 20 angstroms and shows a knobby chromatin structural organization in TEM. The presence of arginine-enriched protamines in both a basal anuran like the ascaphid A. truei and a more advanced neobatrachian like the leptodactylid E. coqui supports the hypothesis that internal fertilization acts as a constraint on the range of SNBP diversity in animals.

Amino Acids↗
PubMed2004

Nucleoplasmin: a nuclear chaperone.

In this article, we briefly review the structural and functional information currently available on nucleoplasmin. Special emphasis is placed on the discussion of the molecular mechanism involved in the sperm chromatin remodelling activity of this protein. A model is proposed based on current crystallographic data, recent biophysical and functional studies, as well as in the previously available information.

Active Transport, Cell Nucleus↗