Ezzat El-Sherif

The University of Texas Rio Grande Valley · School of Integrative Biological and Chemical Sciences

Understanding embryonic patterning, the process by which groups of cells are partitioned into distinct identities defined by gene expression, is a central challenge in developmental biology. This complex phenomenon is driven by precise spatial and temporal regulation of gene expression across many cells, resulting in the emergence of highly organiz...

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called 'enhancers'. Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains across embryonic tissues. Such view has...

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called ‘enhancers.’ Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains across embryonic tissues. Such a view ha...

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called ‘enhancers.’ Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains across embryonic tissues. Such a view ha...

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called ‘enhancers.’ Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains across embryonic tissues. Such a view ha...

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called 'enhancers'. Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains of gene expressions that undergo little...

Oscillatory and sequential processes have been implicated in the spatial patterning of many embryonic tissues. For example, molecular clocks delimit segmental boundaries in vertebrates and insects and mediate lateral root formation in plants, whereas sequential gene activities are involved in the specification of regional identities of insect neuro...

During development, cells gradually assume specialized fates via changes of transcriptional dynamics, sometimes even within the same developmental stage. For anterior-posterior (AP) patterning in metazoans, it has been suggested that the gradual transition from a dynamic genetic regime to a static one is encoded by different transcriptional modules...

During development, cells gradually assume specialized fates via changes of transcriptional dynamics, sometimes even within the same developmental stage. For anterior-posterior (AP) patterning in metazoans, it has been suggested that the gradual transition from a dynamic genetic regime to a static one is encoded by different transcriptional modules...

During development, cells gradually assume specialized fates via changes of transcriptional dynamics, sometimes even within the same developmental stage. For anterior-posterior (AP) patterning in metazoans, it has been suggested that the gradual transition from a dynamic genetic regime to a static one is encoded by different transcriptional modules...

During development, cells gradually assume specialized fates via changes of transcriptional dynamics, sometimes even within the same developmental stage. For anterior-posterior patterning in metazoans, it has been suggested that the gradual transition from a dynamic genetic regime to a static one is encoded by different transcriptional modules. In...

Recently, it was shown that anterior-posterior patterning genes in the red flour beetle Tribolium castaneum are expressed sequentially in waves. However, in the fruit fly Drosophila melanogaster, an insect with a derived mode of embryogenesis compared to Tribolium, anterior-posterior patterning genes quickly and simultaneously arise as mature gene...

Gap genes mediate the division of the anterior-posterior axis of insects into different fates through regulating downstream hox genes. Decades of tinkering the segmentation gene network of Drosophila melanogaster led to the conclusion that gap genes are regulated (at least initially) through a threshold-based mechanism, guided by both anteriorly- a...

Recently, it was shown that anterior-posterior patterning genes in the red flour beetle Tribolium castaneum are expressed sequentially in waves. However, in the fruit fly Drosophila melanogaster, an insect with a derived mode of embryogenesis compared to Tribolium, anterior-posterior patterning genes quickly and simultaneously arise as mature gene...

Gap genes mediate the division of the anterior-posterior axis of insects into different fates through regulating downstream hox genes. Decades of tinkering the segmentation gene network of the long-germ fruit fly Drosophila melanogaster led to the conclusion that gap genes are regulated (at least initially) through a threshold-based French Flag mod...

Using simple animations, mathematical formulations, and computational implementation in Matlab, we present a newly devised embryonic patterning mechanism: the Speed Regulation model, and its molecular realization: the Gradual Enhancer Switching model. We show how our models shed light on the phenomenology of insect development and evolution. Long...

Partitioning an initially homogeneous group of cells into different fates is a common problem in development. A curious case is the anterior-posterior (AP) fate specification during early embryogenesis in insects. The AP fates of most insects are specified in two different phases: (i) the blastoderm, where the AP axis does not undergo any axial elo...

Evolution of cis -properties (such as enhancers) often plays an important role in the production of diverse morphology. However, a mechanistic understanding is often limited by the absence of methods to study enhancers in species outside of established model systems. Here, we sought to establish methods to identify and test enhancer activity in the...

Significance How a homogeneous group of cells is partitioned into domains of different identities is a common problem in embryogenesis. Partitioning, in some cases, takes places within a static tissue field and, in other cases, in a progressively growing tissue. A curious case is the partitioning of insect bodies into a head, thorax, and abdomen, w...

Evolution of cis-properties (such as enhancers) often plays an important role in the production of diverse morphology. However, a mechanistic understanding is often limited by the absence of methods to study enhancers in species outside of established model systems. Here, we sought to establish methods to identify and test enhancer activity in the...

Drosophila patterning genes often contain pairs of primary and shadow enhancers that possess overlapping activities [1-5]. It has been suggested that this regulatory "redundancy" helps ensure reliable activation of gene expression under stressful conditions such as increases in temperature [4, 5]. There is also evidence that shadow enhancers help p...

In the short-germ beetle Tribolium castaneum, waves of pair-rule gene expression propagate from the posterior end of the embryo towards the anterior and eventually freeze into stable stripes, partitioning the anterior-posterior axis into segments. Similar waves in vertebrates are assumed to arise due to the modulation of a molecular clock by a post...

In Drosophila, all segments form in the blastoderm where morphogen gradients spanning the entire anterior-posterior axis of the embryo provide positional information. However, in the beetle Tribolium castaneum and most other arthropods, a number of anterior segments form in the blastoderm, and the remaining segments form sequentially from a posteri...

Studying the embryogenesis of diverse insect species is crucial to understanding insect evolution. Here, we review current advances in understanding the development of two emerging model organisms: the wasp Nasonia vitripennis and the beetle Tribolium castaneum in comparison with the well‐studied fruit fly Drosophila melanogaster . Although Nasonia...

In this section we present some experiments that validate the proposed approach and shed light on its strengths and limitations. 4.1 Model-Based Approach versus DFS The problem of finding optimal classification cascades has other possible solutions than that proposed (e.g. using stochastic search techniques [Chellapilla et al. 2006a]). But we will...

In this paper, we present a novel technique to automatically generate optimum classification cascades. Given a powerful classifier S_F with satisfactory accuracy and a set of N classifiers, our algorithm builds the fastest cascade that achieves an accuracy not less than that of S_F. The algorithm is fully automatic and has a com...

In this paper, we fill a gap in the literature by studying the problem of Arabic handwritten digit recognition. The performances of different classification and feature extraction techniques on recognizing Arabic digits are going to be reported to serve as a benchmark for future work on the problem. The performance of well known classifiers and fea...