Marta Lenartowska

Nicolaus Copernicus University in Toruń · Biology and Environmental Protection, Laboratory of Developmental Biology

Pollen tube growth depends on several complex processes, including exo/endocytosis, cell wall biogenesis, intracellular transport, and cell signaling. Our previous results provided evidence that calreticulin (CRT)—a prominent calcium (Ca2+)-buffering molecular chaperone in the endoplasmic reticulum (ER) lumen—is involved in pollen tube formation an...

A useful model for determining the mechanisms by which actin and actin binding proteins control cellular architecture is the Drosophila melanogaster process of spermatogenesis. During the final step of spermatogenesis, 64 syncytial spermatids individualized as stable actin cones move synchronously down the axonemes and remodel the membranes. To ide...

Background Pollen development in the anther in angiosperms depends on complicated cellular interactions associated with the expression of gametophytic and sporophytic genes which control fundamental processes during microsporo/gametogenesis, such as exo/endocytosis, intracellular transport, cell signaling, chromatin remodeling, and cell division. M...

Spermiogenesis is the final stage of spermatogenesis, a differentiation process during which unpolarized spermatids undergo excessive remodeling that results in the formation of sperm. The actin cytoskeleton and associated actin-binding proteins play crucial roles during this process regulating organelle or vesicle delivery/segregation and forming...

During spermiogenesis in mammals actin filaments and a variety of actin-binding proteins are involved in the formation and function of highly specialized testis-specific structures. Actin-based motor proteins, such as myosin Va and VIIa, play a key role in this complex process of spermatid transformation into mature sperm. We have previously demons...

Myosin VI (MYO6) is an actin-based motor that has been implicated in a wide range of cellular processes, including endocytosis and the regulation of actin dynamics. MYO6 is crucial for actin/membrane remodeling during the final step of Drosophila spermatogenesis, and MYO6-deficient males are sterile. This protein also localizes to actin-rich struct...

Calreticulin (CRT) is a multifunctional resident endoplasmic reticulum (ER) luminal protein implicated in regulating a variety of cellular processes, including Ca⁠2+ storage/mobilization and protein folding. These multiple functions may be carried out by different CRT genes and protein isoforms. The plant CRT family consist of three genes: CRT1 and...

Myosin VI (MVI) is a unique actin-based motor protein moving towards the minus end of actin filaments, in the opposite direction than other known myosins. Besides well described functions of MVI in endocytosis and maintenance of Golgi apparatus, there are few reports showing its involvement in transcription. We previously demonstrated that in neuro...

Calcium (Ca(2+)) plays essential roles in generative reproduction of angiosperms, but the sites and mechanisms of Ca(2+) storage and mobilization during pollen-pistil interactions have not been fully defined. Both external and internal Ca(2+) stores are likely important during male gametophyte communication with the sporophytic and gametophytic cel...

Myosin VI (MVI) is a versatile actin-based motor protein that has been implicated in a variety of different cellular processes, including endo- and exocytic vesicle trafficking, Golgi morphology, and actin structure stabilization. A role for MVI in crucial actin-based processes involved in sperm maturation was demonstrated in Drosophila. Because of...

Main conclusion: Calreticulin is involved in stabilization of the tip-focused Ca (2+) gradient and the actin cytoskeleton arrangement and function that is required for several key processes driving Petunia pollen tube tip growth. Although the precise mechanism is unclear, stabilization of a tip-focused calcium (Ca(2+)) gradient seems to be critica...

Key message: Calreticulin expression is upregulated during sexual reproduction of Hyacinthus orientalis , and the protein is localized both in the cytoplasm and a highly specialized cell wall within the female gametophyte. Several evidences indicate calreticulin (CRT) as an important calcium (Ca(2+))-binding protein that is involved in the generat...

Key message In germinating pollen grains and growing pollen tubes, CRT is translated on ER membrane-bound ribosomes in the regions where its activity is required for stabilization of tip-focused Ca 2+ gradient. Abstract Pollen tube growth requires coordination of signaling, exocytosis, and actin cytoskeletal organization. Many of these processes ar...

Calcium (Ca(2+)) plays essential roles in plant sexual reproduction, but the sites and the mechanism of Ca(2+) mobile storage during pollen-pistil interactions have not been fully defined. Because the Ca(2+)-buffering protein calreticulin (CRT) is able to bind and sequester Ca(2+), it can serve as a mobile intracellular store of easily releasable C...

Myosin VI (MVI), an actin-based molecular motor, is believed to have unique functions in eukaryotic cells, because it is the only myosin shown to move toward the pointed end of actin filaments, in the opposite direction of all other myosins. Given some unusual structural and kinetic properties of MVI, many models of its functioning in variety cellu...

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca(2+)-binding protein in multicellular eukaryotes. As an endoplasmic reticulum-resident protein, CRT plays a key role in many cellular processes including Ca(2+) storage and release, protein synthesis, and molecular chaperoning in both animals and plants. CRT has long been suggest...

Ultrastructure of actin cones is altered when myosin VI is mislocalized in wild-type animals. Examples of S1 decorated actin cones when GFP-HNPMD (Gtail deleted) transgene is expressed in a wild-type animal. Big arrow indicates the direction of cone movement and small arrows indicate asymmetry of cone front domains. mi, mitochondria; ax, axoneme. B...

Ultrastructure of actin cones is altered when myosin VI is mislocalized in mutant animals. Examples of S1 decorated cones when GFP-HNPMD (Gtail deleted) transgene is expressed in myosin VI mutant background. (insets, i–iii), Small regions of actin cones at high magnification. Big arrow indicates the direction of cone movement and small arrows indic...

Actin structures are often stable, remaining unchanged in organization for the lifetime of a differentiated cell. Little is known about stable actin structure formation, organization, or maintenance. During Drosophila spermatid individualization, long-lived actin cones mediate cellular remodeling. Myosin VI is necessary for building the dense meshw...

Stable actin structures play important roles in the development and specialization of differentiated cells. How these structures form, are organized, and are used to mediate physiological processes is not well understood in most cases. In Drosophila testis, stable actin structures, called actin cones, mediate spermatid individualization, a large-sc...

Myosins are actin-based motor proteins that use energy derived from ATP hydrolysis to generate force and move along actin filaments. Myosin VI is a unique motor protein because it moves towards the "minus" end of actin filament, which is the opposite direction to all of the other myosins studied so far, and therefore is thought to have unique prope...

In this report, the localization and spatial distribution of two categories of pectin, high and low methylesterified, on the background of dynamic in loosely bound calcium (Ca(2+)) in Haemanthus hollow style were studied before and after pollination. In the style transmitting tract of unpollinated pistil, mainly high-methylesterified pectins were p...

In this report, the distributions of calreticulin (CRT) and its transcripts in Haemanthus pollen, pollen tubes, and somatic cells of the hollow pistil were studied. Immunoblot analysis of protein extracts from mature anthers, dry and germinated pollen, growing pollen tubes, and unpollinated/pollinated pistils revealed a strong expression of CRT. Bo...

The hypothesis that lead (Pb) can be uptake or remobilized from the cell wall (CW) by internalization withlow-esterified pectins (up to 40%--JIM5-P), was studied in tip-growing apical cell of Funaria hygrometrica protonemata. Treatment 4h with 1mM PbCl(2) caused marked vesicular traffic intensification and the common internalization of JIM5-P from...

Lead poisoning constitutes one of most detrimental environmental hazards to all living organisms. Plants developed a variety of avoidance and tolerance mechanisms that are activated in response to lead exposure. Plant cell walls were suggested to play important role in these reactions by creating an efficient barrier to lead entry to the protoplast...

Calreticulin (CRT) is an ubiquitously expressed Ca2+ binding protein in endoplasmic reticulum (ER) of eukaryotic cells. A highly conserved structure between CRTs from different species of animals and plants confirms an important role of the protein in living cells. CRT has been found in different cellular compartments, suggesting to play a role in...

The actin cytoskeleton plays a crucial role in pollen tube growth. In elongating pollen tubes the organization and arrangement of actin filaments (AFs) differs between the shank and apical region. However, the orientation of AFs in pollen tubes has not yet been successfully demonstrated. In the present work we have used myosin II subfragment 1 (S1)...

During spermatid individualization in Drosophila, actin structures (cones) mediate cellular remodeling that separates the syncytial spermatids into individual cells. These actin cones are composed of two structural domains, a front meshwork and a rear region of parallel bundles. We show here that the two domains form separately in time, are regulat...

It is known that the level of cGMP is modulated in plant cells in response to a number of stimuli but intracellular events dependent on cGMP metabolism are not clear. Guanylyl cyclases (GCs) are enzymes which are responsible for synthesis of cGMP in eukaryotic and prokaryotic cells. To collect evidence for the participation of cGMP in light signal...

Drosophila melanogaster bristle development is dependent on actin assembly, and prominent actin bundles form against the elongating cell membrane, giving the adult bristle its characteristic grooved pattern. Previous work has demonstrated that several actin-regulating proteins are required to generate normal actin bundles. Here we have addressed ho...

Here, we demonstrate a new function of myosin VI using observations of Drosophila spermatid individualization in vivo. We find that myosin VI stabilizes a branched actin network in actin structures (cones) that mediate the separation of the syncytial spermatids. In a myosin VI mutant, the cones do not accumulate F-actin during cone movement, wherea...

The subcellular localization of Ca2+ ions as well as esterified and deesterified pectins in unpollinated and pollinated wet (Petunia hybrida) and dry (Haemanthus albiflos) stigma was analyzed. Stigmas with different surfaces were found to differ in Ca2+ and pectin localization. In a wet Petunia hybrida stigma, Ca2+ ions were present in the exudate...

With a polyclonal antibody raised against calreticulin (CRT) the locations where the protein occurs in unpollinated and pollinated styles of Petunia hybrida were localized. The epitopes binding the CRT antibody were immunolocalized preferentially in pollen tubes. In transmitting tract cells, both before and after pollination, the level of CRT was l...

Localization of pectins in the style of Petunia hybrida before and after pollination was investigated by immunocytochemistry using two primary monoclonal antibodies specific to highly (JIM7) and weakly (JIM5) methylesterified pectins. In the unpollinated style, esterified pectins occurred mainly in the cell walls of cortex tissue, while unesterifie...

The objective of our research on Petunia hybrida is to understand the role of calreticulin in the growth of pollen tubes in the pistil. The aim of this study was the first step: finding out whether CRT gene expression takes place in unpollinated and pollinated styles. It was revealed by in situ hybridization that the transcription of the calreticul...

A commercial anti-calmodulin monoclonal antibody (CaM MAb) was used to determine the presence and localization of calmodulin (CaM) and calmodulin-like protein in unpollinated and pollinated styles of Petunia hybrida. In the unpollinated style, CaM was localized in the cytoplasm of transmitting tract cells. The response to pollination and/or pollen...

The aim of the present study was to find the source of postpollination increase in calcium content in the transmitting tract in the style of Petunia hybrida Hort. Cytochemical and radiographic studies revealed a progressive increase in the level of free and loosely bound calcium ions in the course of successive developmental stages of the pollen tu...

The object of study was to reveal the source of the postpollination elevation of [Ca2+] in the extracellular regions of the transmitting tract in Petunia hybrida. In the studies were used: the pyroantimonate method and the immunogold method with the use of monoclonal antibodies JIM5 and JIM7 at the electron microscope level. The subcellular localiz...