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Francisco Pelegri

Publications and source records attributed to Francisco Pelegri.

8 recordsLinked to original sources
PubMed2006

A role for non-muscle myosin II function in furrow maturation in the early zebrafish embryo.

Cytokinesis in early zebrafish embryos involves coordinated changes in the f-actin- and microtubule-based cytoskeleton, and the recruitment of adhesion junction components to the furrow. We show that exposure to inhibitors of non-muscle myosin II function does not affect furrow ingression during the early cleavage cycles but interferes with the recruitment of pericleavage f-actin and cortical beta-catenin aggregates to the furrow, as well as the remodeling of the furrow microtubule array. This remodeling is in turn required for the distal aggregation of the zebrafish germ plasm. Embryos with reduced myosin activity also exhibit at late stages of cytokinesis a stabilized contractile ring apparatus that appears as a ladder-like pattern of short f-actin cables, supporting a role for myosin function in the disassembly of the contractile ring after furrow formation. Our studies support a role for myosin function in furrow maturation that is independent of furrow ingression and which is essential for the recruitment of furrow components and the remodeling of the cytoskeleton during cytokinesis.

Actins↗
PubMed2006

bmp1 and mini fin are functionally redundant in regulating formation of the zebrafish dorsoventral axis.

Drosophila metalloproteinase Tolloid (TLD) is responsible for cleaving the antagonist Short gastrulation (SOG), thereby regulating signaling by the bone morphogenetic protein (BMP) Decapentaplegic (DPP). In mice there are four TLD-related proteinases, two of which, BMP1 and mammalian Tolloid-like 1 (mTLL1), are responsible for cleaving the SOG orthologue Chordin, thereby regulating signaling by DPP orthologues BMP2 and 4. However, although TLD mutations markedly dorsalize Drosophila embryos, mice doubly homozygous null for BMP1 and mTLL1 genes are not dorsalized in early development. Only a single TLD-related proteinase has previously been reported for zebrafish, and mutation of the zebrafish TLD gene (mini fin) results only in mild dorsalization, manifested by loss of the most ventral cell types of the tail. Here we identify and map the zebrafish BMP1 gene bmp1. Knockdown of BMP1 expression results in a mild tail phenotype. However, simultaneous knockdown of mini fin and bmp1 results in severe dorsalization resembling the Swirl (swr) and Snailhouse (snh) phenotypes; caused by defects in major zebrafish ventralizing genes bmp2b and bmp7, respectively. We conclude that bmp1 and mfn gene products functionally overlap and are together responsible for a key portion of the Chordin processing activity necessary to formation of the zebrafish dorsoventral axis.

Amino Acid Sequence↗
PubMed2006

Separate pathways of RNA recruitment lead to the compartmentalization of the zebrafish germ plasm.

The maternal RNAs vasa, dead end, nanos1, and daz-like all become localized to the peripheral ends of the first and second cleavage furrows, where they form part of the zebrafish germ plasm. We show that aggregates of a first class of germ plasm components, which include dead end, nanos1, and vasa RNAs, are initially present in a wide cortical band at the animal pole. Aggregates containing these three RNAs appear to be associated with f-actin, which during the first cell cycle undergoes a microtubule-dependent movement towards the periphery as well as circumferential alignment. These cytoskeletal rearrangements lead to the further aggregation of particles containing these RNAs and their concomitant recruitment to the forming furrow. Aggregates containing a second class of germ plasm RNA components, which include the transcript for daz-like, translocate along the plane of the cortex towards the animal pole, where they are recruited to the germ plasm. After recruitment to the furrow, these two classes of RNAs occupy overlapping yet distinct regions of the germ plasm, and this arrangement is maintained during the early cleavage stages. Our observations suggest that separate pathways of RNA recruitment facilitate the compartmentalization of the zebrafish germ plasm.

Actins↗
PubMed2006

Analysis of axis induction mutant embryos reveals morphogenetic events associated with zebrafish yolk extension formation.

We analyze patterning and morphogenetic events during somitogenesis in hecate mutant embryos, which exhibit early axis induction defects. The posterior region, in the absence of a dorsal axis, is capable of forming organized gene expression patterns. The aberrant morphogenesis of mutant embryos is associated with anteriorly directed cell movements, underlying the enveloping layer, from the posterior region. In both wild-type and mutant embryos, these changes result in an accumulation of cells, whose location correlates with a constriction in the posterior yolk cell, which in the wild-type corresponds to the yolk extension. The region encompassing the constriction corresponds to a region of expression of zangptl2 in the yolk syncytial layer, which expands anteriorly together with the anteriorly migrating tail bud-derived cell population. Our data indicate that yolk extension formation is associated with coordinated changes involving the anterior migration of cells from the posterior region, changes in surface cellular layers, and inductive gene expression events in the YSL.

Actins↗
PubMed2005

hecate, a zebrafish maternal effect gene, affects dorsal organizer induction and intracellular calcium transient frequency.

A zebrafish maternal effect mutation, in the gene hecate, results in embryos that have defects in the formation of dorsoanterior structures and altered calcium release. hecate mutant embryos lack nuclear accumulation of beta-catenin and have reduced expression of genes specific to the dorsal organizer. We found that hecate mutant embryos exhibit a nearly 10-fold increase in the frequency of intracellular Ca2+ transients normally present in the enveloping layer during the blastula stages. Inhibition of Ca2+ release leads to ectopic expression of dorsal genes in mutant embryos suggesting that Ca2+ transients are important in mediating dorsal gene expression. Inhibition of Ca2+ release also results in the expression of dorsal-specific genes in the enveloping layer in a beta-catenin-independent manner, which suggests an additional function for the Ca2+ transients in this cellular layer. The mutant phenotype can be reversed by the expression of factors that activate Wnt/beta-catenin signaling, suggesting that the Wnt/beta-catenin pathway, at least as activated by an exogenous Wnt ligand, is intact in hec mutant embryos. Our results are consistent with a role for the hecate gene in the regulation of Ca2+ release during the cleavage stages, which in turn influences dorsal gene expression in both marginal cells along the dorsoventral axis and in the enveloping layer.

Animals↗
PubMed2004

Identification of recessive maternal-effect mutations in the zebrafish using a gynogenesis-based method.

In animal species, early developmental processes are driven by maternally derived factors. Here, we describe a forward genetics approach to identify recessive mutations in genes encoding such maternal factors in the zebrafish. We used a gynogenesis-based approach to identify 14 recessive maternal-effect mutations. Homozygosity for these mutations in adult females leads to the inviability of their offspring. Confocal microscopy of embryos labeled with a DNA dye and a membrane marker allowed us to further analyze mutant embryos for defects in nuclear and cellular divisions. The mutations result in a range of defects in early developmental processes, including egg activation, early nuclear events, mitosis, cytokinesis, axial patterning, and gastrulation. Our effort constitutes a systematic attempt to identify maternal-effect genes in a vertebrate species. The sample of mutations that we have identified reflects the diversity of maternally driven functions in early development and underscores the importance of maternal factors in this process.

Animals↗
PubMed2003

Maternal factors in zebrafish development.

All processes that occur before the activation of the zygotic genome at the midblastula transition are driven by maternal products, which are produced during oogenesis and stored in the mature oocyte. Upon egg activation and fertilization, these maternal factors initiate developmental cascades that carry out the embryonic developmental program. Even after the initiation of zygotic gene expression, perduring maternal products continue performing essential functions, either together with other maternal factors or through interactions with newly expressed zygotic products. Advances in zebrafish research have placed this organism in a unique position to contribute to a detailed understanding of the role of maternal factors in early vertebrate development. This review summarizes our knowledge on the processes involved in the production and redistribution of maternal factors during zebrafish oogenesis and early development, as well as our understanding of the function of these factors in axis formation, germ layer and germ cell specification, and other early embryonic processes.

Animals↗