Biology subjects

Posnien, N.

Publications and source records attributed to Posnien, N..

8 recordsLinked to original sources

bioRxiv2021

Differences in orthodenticle expression promote ommatidial size variation between Drosophila species

The compound eyes of insects exhibit extensive variation in ommatidia number and size, which affects how they see and underlies adaptations in their vision to different environments and lifestyles. However, very little is known about the genetic and developmental bases of differences in compound eye size. We previously showed that the larger eyes of Drosophila mauritiana compared to D. simulans is generally caused by differences in ommatidia size rather than number. Furthermore, we identified an X-linked chromosomal region in D. mauritiana that results in larger eyes when introgressed into D. simulans. Here, we used a combination of fine-scale mapping and gene expression analysis to further investigate positional candidate genes on the X chromosome. We found earlier expression of orthodenticle (otd) during ommatidial maturation in third instar larvae in D. mauritiana than in D. simulans, and we show that this gene is required for the correct organisation and size of ommatidia in D. melanogaster. We discovered that the activity of an otd eye enhancer is consistent with the difference in the expression of this gene between species, with the D. mauritiana enhancer sequence driving earlier expression than that of D. simulans. We also identified potential direct targets of Otd that are differentially expressed between D. mauritiana and D. simulans during ommatidial maturation. Taken together, our results suggest that differential timing of otd expression contributes to natural variation in ommatidia size between D. mauritiana and D. simulans, which provides new insights into the mechanisms underlying the regulation and evolution of compound eye size in insects.

evolutionary biology↗

bioRxiv2020

Multiple loci linked to inversions are associated with eye size variation in species of the Drosophila virilis phylad

The size and shape of organs is tightly controlled to achieve optimal function. Natural morphological variations often represent functional adaptations to an ever-changing environment. For instance, variation in head morphology is pervasive in insects and the underlying molecular basis is starting to be revealed in the Drosophila genus for species of the melanogaster group. However, it remains unclear whether similar diversifications are governed by similar or different molecular mechanisms over longer timescales. To address this issue, we used species of the virilis phylad because they have been diverging from D. melanogaster for at least 40 million years. Our comprehensive morphological survey revealed remarkable differences in eye size and head shape among these species with D. novamexicana having the smallest eyes and southern D. americana populations having the largest eyes. We show that the genetic architecture underlying eye size variation is complex with multiple associated genetic variants located on most chromosomes. Our genome wide association study (GWAS) strongly suggests that some of the putative causative variants are associated with the presence of inversions. Indeed, northern populations of D. americana share derived inversions with D. novamexicana and they show smaller eyes compared to southern ones. Intriguingly, we observed a significant enrichment of genes involved in eye development on the 4th chromosome after intersecting chromosomal regions associated with phenotypic differences with those showing high differentiation among D. americana populations. We propose that variants associated with chromosomal inversions contribute to both intra- and inter-specific variation in eye size among species of the virilis phylad.

evolutionary biology↗

bioRxiv2020

Variation in a pleiotropic regulatory module drives evolution of head shape and eye size in Drosophila

Revealing the mechanisms underlying the breath-taking morphological diversity observed in nature is a major challenge in Biology. It has been established that recurrent mutations in hotspot genes cause the repeated evolution of rather simple morphological traits, such as body pigmentation or the gain and loss of structures. To date, however, it remains elusive whether hotspot genes contribute to natural variation in complex morphological traits, such as the size and shape of organs. Since natural variation in head morphology is pervasive in Drosophila, we studied the molecular and developmental basis of differences in compound eye size and head shape in two closely related Drosophila species. We show that differences in both traits are established late during head development and we applied comparative transcriptomics and chromatin accessibility data to identify the GATA transcription factor Pannier (Pnr) as central factor regulating these differences. Although the genetic manipulation of Pnr affected multiple aspects of dorsal head development, the effect of natural variation is restricted to a subset of the phenotypic space. We present data suggesting that this developmental constraint is caused by the co-evolution of expression of pnr and its co-factor u-shaped (ush). We propose that natural variation in highly connected developmental regulators with pleiotropic functions is a major driver for morphological evolution and we discuss implications on gene regulatory network evolution. In comparison to previous findings, our data strongly suggests that evolutionary hotspots do not contribute to the repeated evolution of eye size and head shape in Drosophila.

evolutionary biology↗

bioRxiv2018

Genomic analysis of European Drosophila melanogaster populations on a dense spatial scale reveals longitudinal population structure and continent-wide selection

Genetic variation is the fuel of evolution, with standing genetic variation especially important for short-term evolution and local adaptation. To date, studies of spatio-temporal patterns of genetic variation in natural populations have been challenging, as comprehensive sampling is logistically difficult, and sequencing of entire populations costly. Here, we address these issues using a collaborative approach, sequencing 48 pooled population samples from 32 locations, and perform the first continent-wide genomic analysis of genetic variation in European Drosophila melanogaster. Our analyses uncover longitudinal population structure, provide evidence for continent-wide selective sweeps, identify candidate genes for local climate adaptation, and document clines in chromosomal inversion and transposable element frequencies. We also characterise variation among populations in the composition of the fly microbiome, and identify five new DNA viruses in our samples.

evolutionary biology↗

bioRxiv2017

Extensive Sexual Wing Shape Dimorphism In Drosophila melanogaster, Ceratitis capitata, And Musca domestica

The ability of powered flight in insects facilitated their great evolutionary success allowing them to occupy various ecological niches. Beyond this primary task, wings are often involved in various premating behaviors, such as the generation of courtship songs and the initiation of mating in flight. These specific functions imply special adaptations of wing morphology, as well as sex-specific wing morphologies. Although wing morphology has been extensively studied in Drosophila melanogaster, a comprehensive understa nding of sexual wing shape dimorphisms and developmental plasticity is missing for other Diptera. Therefore, we raised flies of the three Diptera species Drosophila melanogaster, Ceratitis capitata and Musca domestica at different environmental conditions and applied geometric morphometrics to analyze wing shape. Our data showed extensive interspecific differences in wing shape, as well as a clear sexual wing shape dimorphism in all three species. We revealed an impact of different rearing temperatures wing shape in all three species, which was mostly explained by plasticity in wing size in D. melanogaster. Rearing densities had significant effects on allometric wing shape in D. melanogaster, while no obvious effects were observed for the other two species. Additionally, we do not find evidence for sex-specific response to different rearing conditions in all three species. We determined species-specific and common trends in shape alterations, and we hypothesize developmental and functional implications of our data. Contribution to the Field StatementThe size and shape of organisms and organs must be tightly controlled during development to ensure proper functionality. However, morphological traits vary considerably in nature contributing to phenotypic diversity. Such variation can be the result of evolutionary adaptations as well as plasticity for example as reaction to changing environmental conditions during development. It is therefore a major aim in Biology to unravel the processes that control differences in adult morphology. Insect wings are excellent models to study how organ size and shape evolves because they facilitate basic tasks such as mating and feeding. Accordingly, a tremendous variety of wings sizes and shapes evolved in nature. Additionally, plasticity in wing morphology in response to different rearing conditions has been observed in many insects contributing to phenotypic diversity. In this work we applied Geometric Morphometrics to study wing shape in the three Diptera species: the Mediterranean fruit fly Ceratitis capitata, the Vinegar fly Drosophila melanogaster and the housefly Musca domestica. Flies were raised in different temperature and density regimes that allowed us to study the effects of these environmental factors on wing shape. Additionally, in accordance with different mating behaviors of these flies, we observed a clear sexual shape dimorphism in all three species. Since the three studied species represent serious pests and disease vectors, our findings may contribute to existing and future monitoring efforts.

zoology↗

bioRxiv2017

A novel role for Ets4 in axis specification and cell migration in the spider Parasteatoda tepidariorum

Organizers play important roles during the embryonic development of many animals. The most famous example is the Spemann organizer that sets up embryonic axes in amphibian embryos.\n\nIn spiders, a group of BMP secreting mesenchymal cells (the cumulus) functions as an organizer of the dorsoventral axis. Similar to experiments performed with the Spemann organizer, transplantation of the cumulus is able to induce a secondary axis in spiders.\n\nDespite the importance of this structure, it is unknown which factors are needed to activate cumulus specific gene expression.\n\nTo address this question, we performed a transcriptomic analysis of early embryonic development in the spider Parasteatoda tepidariorum. Through this work, we found that the transcription factor Pt-Ets4 is needed for cumulus integrity, dorsoventral patterning and for the activation of Pt-hunchback and Pt-twist expression. Furthermore, ectopic expression of Pt-Ets4 is sufficient to induce cell delamination and migration by inducing a mesoderm-like cell fate.

developmental biology↗

bioRxiv2017

Dynamic genome wide expression profiling of Drosophila head development reveals a novel role of Hunchback in retinal glia cell development and blood-brain barrier integrity

The development of different cell types must be tightly coordinated in different organs. The developing head of Drosophila melanogaster represents an excellent model to study the molecular mechanisms underlying this coordination because the eye-antennal imaginal discs contain the organ anlagen of nearly all adult head structures, such as the compound eyes or the antennae. We studied the genome wide gene expression dynamics during eye-antennal disc development in D. melanogaster to identify new central regulators of the underlying gene regulatory network. Expression based gene clustering and transcription factor motif enrichment analyses revealed a central regulatory role of the transcription factor Hunchback (Hb). We confirmed that hb is expressed in two polyploid retinal subperineurial glia cells (carpet cells). Our functional analysis shows that Hb is necessary for carpet cell development and loss of Hb function results in abnormal glia cell migration and photoreceptor axon guidance patterns. Additionally, we show for the first time that the carpet cells are an integral part of the blood-brain barrier.

developmental biology↗

bioRxiv2016

Specific expression and function of the Six3 optix in serially homologous organs

Organ size and pattern results from the integration of two positional information systems. One global, encoded by the Hox genes, links organ type with position along the main body axis. Within specific organs, local information is conveyed by signaling molecules that regulate organ growth and pattern. The mesothoracic (T2) wing and the metathoracic (T3) haltere of Drosophila represent a paradigmatic example of this coordination. The Hox gene Ultrabithorax (Ubx), expressed in the developing T3, selects haltere identity by, among other processes, modulating the production and signaling efficiency of Dpp, a BMP2-like molecule that acts as a major regulator of size and pattern. Still, the mechanisms of the Hox-signal integration even in this well-studied system, are incomplete. Here we have investigated this issue by studying the expression and function of the Six3 transcription factor optix during the development of the Drosophila wing and haltere development. We find that in both organs Dpp defines the expression domain of optix through repression, and that the specific position of this domain in wing and haltere seems to reflect the differential signaling profile among these organs. We show that optix expression in wing and haltere primordia is conserved beyond Drosophila in other higher diptera. Despite the similar expression pattern, optix plays different roles in wing and haltere. In the wing, optix is required for the growth of the most anterior/proximal region (the \"marginal cell\") and for the correct formation of sensory structures along the proximal anterior wing margin. In contrast, in the haltere optix is necessary for the suppression of sensory bristles without any noticeable effect on organ growth. Therefore, optix shows an organ-specific function. Beyond dipterans, optix expression in the anterior wing has been shown also in butterflies. We propose that the ancestral role of optix might have been structural in the anterior wing. Once expressed in the wing, optix expression had been re-deployed for wing spot formation in other parts of the wing of Heliconius butterflies.

developmental biology↗