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A González-Reyes

Publications and source records attributed to A González-Reyes.

17 recordsLinked to original sources
PubMed2006

Genetic dissection of a stem cell niche: the case of the Drosophila ovary.

In this work, we demonstrate a powerful new tool for the manipulation of the stromal component of a well-established Drosophila stem cell niche. We have generated a bric-a-brac 1 (bab1)-Gal4 line that drives UAS expression in many somatic ovary cell types from early larval stages. Using this Gal4 line, we could effectively induce FLP/FRT-mediated recombination in the stromal cells of the ovarian germline stem cell niche. Mutant clones were observed in the developing ovary of larvae and pupae, including in somatic cell types that do not divide in the adult, such as the cap cells and the terminal filament cells. Exploiting the ability of bab1-Gal4 to generate large clones, we demonstrate that bab1-Gal4 is an effective tool for analyzing stem cell niche morphogenesis and cyst formation in the germarium. We have identified a novel requirement for engrailed in the correct organization of the terminal filaments. We also demonstrate an involvement for integrins in cyst formation and follicle cell encapsulation. Finally using bab1-Gal4 in conjunction with the Gal80 system, we show that while ectopic dpp expression from stromal cells is sufficient to induce hyperplastic stem cell growth, neither activation nor inactivation of the BMP pathway within stromal cells affects germline stem cell maintenance.

Animals↗
PubMed2001

Centrosome migration into the Drosophila oocyte is independent of BicD and egl, and of the organisation of the microtubule cytoskeleton.

During early Drosophila oogenesis, one cell from a cyst of 16 germ cells is selected to become the oocyte, and accumulates oocyte-specific proteins and the centrosomes from the other 15 cells. Here we show that the microtubule cytoskeleton and the centrosomes follow the same stepwise restriction to one cell as other oocyte markers. Surprisingly, the centrosomes still localise to one cell after colcemid treatment, and in BicD and egl mutants, which abolish the localisation of all other oocyte markers and the polarisation of the microtubule cytoskeleton. In contrast, the centrosomes fail to migrate in cysts mutant for Dynein heavy chain 64C, which disrupts the fusome. Thus, centrosome migration is independent of the organisation of the microtubule cytoskeleton, and seems to depend instead on the polarity of the fusome.

Animals↗
PubMed1998

Patterning of the follicle cell epithelium along the anterior-posterior axis during Drosophila oogenesis.

Gurken signals from the oocyte to the adjacent follicle cells twice during Drosophila oogenesis; first to induce posterior fate, thereby polarising the anterior-posterior axis of the future embryo and then to induce dorsal fate and polarise the dorsal-ventral axis. Here we show that Gurken induces two different follicle cell fates because the follicle cells at the termini of the egg chamber differ in their competence to respond to Gurken from the main-body follicle cells in between. By removing the putative Gurken receptor, Egfr, in clones of cells, we show that Gurken signals directly to induce posterior fate in about 200 cells, defining a terminal competence domain that extends 10-11 cell diameters from the pole. Furthermore, small clones of Egfr mutant cells at the posterior interpret their position with respect to the pole and differentiate as the appropriate anterior cell type. Thus, the two terminal follicle cell populations contain a symmetric prepattern that is independent of Gurken signalling. These results suggest a three-step model for the anterior-posterior patterning of the follicular epithelium that subdivides this axis into at least five distinct cell types. Finally, we show that Notch plays a role in both the specification and patterning of the terminal follicle cells, providing a possible explanation for the defect in anterior-posterior axis formation caused by Notch and Delta mutants.

Animals↗
PubMed1998

The Drosophila AP axis is polarised by the cadherin-mediated positioning of the oocyte.

The anterior-posterior axis of Drosophila originates from two symmetry-breaking steps during early oogenesis. First, one of the two pro-oocytes within the cyst of 16 germline cells is selected to become the oocyte. This cell then comes to lie posterior to the other germline cells of the cyst, thereby defining the polarity of the axis. Here we show that the oocyte reaches the posterior of the cyst in two steps. (1) The cyst flattens as it enters region 2b of the germarium to place the two pro-oocytes in the centre of the cyst, where they contact the posterior follicle cells. (2) One cell is selected to become the oocyte and protrudes into the posterior follicle cell layer when the cyst rounds up on entering region 3. During this germ cell rearrangement, the components of the homophilic cadherin adhesion complex, DE-cadherin, Armadillo and alpha-catenin, accumulate along the border between the oocyte and the posterior follicle cells. Furthermore, the positioning of the oocyte requires cadherin-dependent adhesion between these two cell types, since the oocyte is frequently misplaced when DE-cadherin is removed from either the germline or the posterior follicle cells. We conclude that the oocyte reaches the posterior of the germline cyst because it adheres more strongly to the posterior follicle cells than its neighbours during the germ cell rearrangement that occurs as the cyst moves into region 3. The Drosophila anterior-posterior axis therefore becomes polarised by an unusual cadherin-mediated adhesion between a germ cell and mesodermal follicle cells.

Alleles↗
PubMed1997

The mago nashi gene is required for the polarisation of the oocyte and the formation of perpendicular axes in Drosophila.

BACKGROUND: Drosophila axis formation requires a series of inductive interactions between the oocyte and the somatic follicle cells. Early in oogenesis, Gurken protein, a member of the transforming growth factor alpha family, is produced by the oocyte to induce the adiacent follicle cells to adopt a posterior cell fate. These cells subsequently send an unidentified signal back to the oocyte to induce the formation of a polarised microtubule array that defines the anterior-posterior axis. The polarised microtubules also direct the movement of the nucleus and gurken mRNA from the posterior to the anterior of the oocyte, where Gurken signals a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis. RESULTS: In addition to its previously described role in the localisation of oskar mRNA, the mago nashi gene is required in the germ line for the transduction of the polarising signal from the posterior follicle cells. Using a new in vivo marker for microtubules, we show that mago nashi mutant oocytes develop a symmetric microtubule cytoskeleton that leads to the transient localisation of bicoid mRNA to both poles. Furthermore, the oocyte nucleus often fails to migrate to the anterior, causing the second Gurken signal to be sent in the same direction as the first. This results in a novel phenotype in which the anterior of the egg is ventralised and the posterior dorsalised, demonstrating that the migration of the oocyte nucleus determines the relative orientation of the two principal axes of Drosophila. The mago nashi gene is highly conserved from plants to animals, and encodes a protein that is predominantly localised to nuclei. CONCLUSIONS: The mago nashi gene plays two essential roles in Drosophila axis formation: it is required downstream of the signal from the posterior follicle cells for the polarisation of the oocyte microtubule cytoskeleton, and has a second, independent role in the localisation of oskar mRNA to the posterior of the oocyte.

Amino Acid Sequence↗
PubMed1997

Oocyte determination and the origin of polarity in Drosophila: the role of the spindle genes.

The two main body axes in Drosophila become polarised as a result of a series of symmetry-breaking steps during oogenesis. Two of the sixteen germline cells in each egg chamber develop as pro-oocytes, and the first asymmetry arises when one of these cells is selected to become the oocyte. Anterior-posterior polarity originates when the oocyte then comes to lie posterior to the nurse cells and signals through the Gurken/Egfr pathway to induce the adjacent follicle cells to adopt a posterior fate. This directs the movement of the germinal vesicle and associated gurken mRNA from the posterior to an anterior corner of the oocyte, where Gurken protein signals for a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis. Here we describe a group of five genes, the spindle loci, which are required for each of these polarising events. spindle mutants inhibit the induction of both the posterior and dorsal follicle cells by disrupting the localisation and translation of gurken mRNA. Moreover, the oocyte often fails to reach the posterior of mutant egg chambers and differentiates abnormally. Finally, double mutants cause both pro-oocytes to develop as oocytes, by delaying the choice between these two cells. Thus, these mutants reveal a novel link between oocyte selection, oocyte positioning and axis formation in Drosophila, leading us to propose that the spindle genes act in a process that is common to several of these events.

Animals↗
PubMed1995

Polarization of both major body axes in Drosophila by gurken-torpedo signalling.

Anterior-posterior polarity in Drosophila arises from the movement of the oocyte to the posterior of the egg chamber, and the subsequent acquisition of posterior fate by the adjacent somatic follicle cells. We demonstrate that gurken is necessary in the oocyte and torpedo/DER in the follicle cells for the induction of posterior fate. As the gurken-torpedo/DER pathway also establishes dorsoventral polarity later in oogenesis, Drosophila uses the same germline to soma signalling pathway to determine both embryonic axes.

Animals↗
PubMed1994

Role of oocyte position in establishment of anterior-posterior polarity in Drosophila.

The polarized microtubule cytoskeleton of the Drosophila oocyte directs the localization of the maternal determinants which establish the anterior-posterior (AP) axis of the embryo. Because the formation of this microtubule array is dependent on signals from the follicle cells that surround the oocyte, it has been proposed that AP polarity originates in the follicle cells. Here it is shown that the movement of the oocyte to the posterior of the egg chamber early in oogenesis determines AP polarity in the follicle cell layer, and also in the oocyte. Moreover, the generation of AP asymmetry requires signaling from the germ line to the soma and back again.

Animals↗
PubMed1994

Developmental consequences of unrestricted expression of the abd-A gene of Drosophila.

The abdominal-A (abd-A) gene of Drosophila specifies abdominal segments two through eight (A2-A8). We have found that the uniform expression of the abd-A protein under heat shock control transforms embryonic segments anterior to the abd-A domain into an abdominal segment of the A2-A6 type. Posterior abdominal segments and telson undergo little or no transformation, that is, the abd-A product is phenotypically suppressed posterior to its realm of expression. The comparison of wildtype embryos with embryos carrying the heat shock-abd-A construct but no abd-A endogenous product indicate that some elements of the pattern-like shape of denticle belts or ventral pits depend on the amount of abd-A protein. The concurrent expression of abd-A and other homeotic genes suggest competition for common downstream genes. This competition has been studied by looking at the expression on the visceral mesoderm of a gene downstream of abd-A, decapentaplegic, when two homeoproteins with opposing effects on its transcription are simultaneously induced.

Abdomen↗
PubMed1992

Trans regulation in the Ultrabithorax gene of Drosophila: alterations in the promoter enhance transvection.

We report a genetic and molecular study of UbxMX6 and Ubx195rx1, two mutations in the Ultrabithorax (Ubx) locus which appear to have a strong effect on the activity of the homologous Ubx gene. These mutations show the characteristic embryonic and adult phenotypes of Ubx null alleles, and also fail to produce any detectable Ubx product. Yet, genetic and phenotypic analyses involving a large number of trans heterozygous combinations of UbxMX6 and Ubx195rx1 with different classes of Ubx mutations, indicate that they hyperactivate the homologous gene. This effect is induced on wildtype or mutant forms of Ubx, provided that the pairing in the bithorax region is normal, i.e. these mutations have a strong positive effect on transvection. We also show that, unlike all the other known cases of transvection in Ubx, this is not zeste-dependent. Southern analyses indicate that UbxMX6 is a 3.4 kb deletion, and Ubx195rx1 is an approximately 11 kb insertion of foreign DNA, both in the promoter region. We speculate that the region altered in the mutations may have a wildtype function to ensure cis-autonomy of the regulation of Ubx transcription.

Alleles↗
PubMed1992

Autocatalysis and phenotypic expression of Drosophila homeotic gene Deformed: its dependence on polarity and homeotic gene function.

Previously published experiments have shown that the endogenous Dfd gene can be ectopically activated by its own (heat-shock-driven) product in a subset of cells of different segments. This results in the differentiation of maxillary structures like cirri and mouth hooks in places where they normally do not appear, and represents a phenomenon of autocatalysis of homeotic gene function that differs from the normal activation process. We show that this out-of-context activation occurs in cells belonging to the anterior compartments of the three thoracic and the A1 to A8 abdominal segments and that it requires the normal function of the polarity genes wingless (wg) and engrailed (en). The wg product, in addition to that of Dfd, appears to be sufficient to activate the endogenous Dfd gene in many embryonic cells. We have studied the effect of several homeotic genes on Dfd activation and phenotypic expression: Scr, Antp, Ubx and Abd-B repress Dfd both transcriptionally and at the phenotypic level, if their products are in sufficient amounts. The endogenous abd-A gene does not have a noticeable effect, but when it is replaced by an hsp70-abd-A gene, which produces a high and uniform level of expression, the phenotypic expression of Dfd is suppressed. Our results also suggest that the differentiation of cirri is induced by Dfd-expressing cells in non-expressing neighboring cells, and that this interaction occurs across the parasegmental border.

Animals↗
PubMed1991

Organization of the Drosophila head as revealed by the ectopic expression of the Ultrabithorax product.

By using a hsp70-Ubx fusion gene, we have ectopically expressed a Ubx product in the embryonic head primordia and studied the developmental effects on the larval head. We find that after high and persistent levels of Ubx product, the head is replaced by three (C1, C2 and C3) abdominal-like denticle belts. The C2 and C3 belts are the homeotic transformations of parasegments 1 and 2, respectively, while the C1 belt probably derives from the transformation and subsequent fusion of the most anterior procephalic primordia. On the basis of their response to the Ubx product and other arguments, we propose that the larval head is made of two genetically distinct components; one is the procephalon and the anterior region of the mandibular lobe, and the other is part of the parasegmental trunk and includes parasegments 1 and 2. Our results also indicate that most or all the larval head structures derive from precursor cells of ventral origin.

Animals↗
PubMed1990

The developmental effect of overexpressing a Ubx product in Drosophila embryos is dependent on its interactions with other homeotic products.

We report the developmental effects of expressing an Ultrabithorax (Ubx) product under the hsp70 promoter. Heat induction gives rise to a high, ubiquitous expression of Ubx product that lasts for several hours. We find that whether or not the overexpression of Ubx has a developmental effect on a particular body region of the larva depends on the interactions with the resident homeotic genes. In head and thorax the Ubx product overrides Sex combs reduced, Antennapedia, and probably other homeotic genes and dictates its own developmental program. In abdominal segments A1-A8 the overexpressed Ubx product establishes a normal pattern, alone (A1) or in combination with abdominal-A (A2-A4) and Abdominal-B (A5-A8), indicating that the excess of product is irrelevant. In segment A9 the highly expressed Ubx product is phenotypically suppressed by the r product of Abdominal-B. The presence of high levels of Ubx protein is also irrelevant in the telson.

Animals↗
PubMed1990

Are cross-regulatory interactions between homoeotic genes functionally significant?

The first instar larva of Drosophila consists of a chain of segments or parasegments in which the morphological pattern characteristic of each metamere is determined by the homoeotic genes, which are active in overlapping domains and are known to interact among themselves. The interactions occur at the level of transcription and allow some homoeotic genes to control the patterns and levels of expression of others. The best known among them are the down-regulation of Antennapedia (Antp) by Ultrabithorax (Ubx) and that of Ubx by abdominal-A (abd-A) and Abdominal-B (Abd-B). It has been proposed that these cross-regulatory interactions play a part in specifying cell pattern, and hence the identity of each metamere. Here we assess the functional significance of some of these interactions by expressing the Antp, Ubx or both homoeotic genes under the control of the heat-shock promoter. Predictably, we find that homoeotic gene products evade normal regulatory controls and can be maximally expressed in regions where they are normally down-regulated but, surprisingly, we find that interruption of the normal down-regulation of Antp and Ubx has no phenotypic consequences in the epidermis, where homoeotic phenotypes are normally manifest. Hence our results challenge the view that these, and possibly other cross-regulatory interactions have a role in determining segmental identity.

Animals↗
PubMed1990

Homoeotic genes.

Region specific differentiation in Drosophila, (and possibly in many other higher organisms), is controlled by the activity of families of transcription factors encoded by the homoeotic genes. In Drosophila these genes are clustered in two complexes: the Antennapedia complex is responsible for directing the differentiation of the head and thoracic body segments whereas the bithorax complex controls the differentiation of the thorax and abdomen. The precise way in which these genes work is still a mystery but both the levels and combinations of gene activities play an important role in directing the development of individual segments.

Animals↗
PubMedDate not supplied

Functional decline and nutritional status in a hospitalized geriatric population: sequential study.

We analyzed the relations between nutritional status and several measures of the ability to perform the normal activities of daily living (ADL) in a long-term institutionalized geriatric population and also studied whether changes in this ability, as found ten months later, were associated with changes in the nutritional status. Nutritional status was assessed using objective anthropometric measurements (triceps skinfold, mid upper-arm circumference, midarm muscle area [AMA], midarm fat area [AFA]) and subjective clinical features (temporal muscle atrophy [TMA] and Bichat's fat atrophy [BFA]). The capacity to perform ADL was analyzed considering ability to eat and to walk, dental status, and mental performance status. Patients with total absence or loss of more than 50% of the teeth showed less AMA and AFA and greater degrees of TMA and BFA; the same happened with regard to deterioration of mental performance status. Those patients fed through a nasogastric tube showed less AFA and serum albumin and also a greater degree of TMA and BFA. Patients unable to walk without aid showed less AMA and AFA. Patients whose capacity to walk improved or whose mental performance status ameliorated showed an increase of their AMA, whereas AFA slightly decreased in those patients whose abilities to eat and to walk deteriorated. Long-term hospitalization in our center led to improvement and to deterioration of ADL in approximately the same number of patients, and similar changes were seen in the nutritional measures.

Activities of Daily Living↗