Biomedical subjects

Isabel Palmeirim

Publications and source records attributed to Isabel Palmeirim.

5 recordsLinked to original sources

PubMed2006

Molecular characterization of the rostral-most somites in early somitic stages of the chick embryo.

Segmentation consists on the progressive formation of repetitive embryonic structures, named somites, which are formed from the most rostral part of the presomitic mesoderm. Somites are subdivided into anterior and posterior compartments and several genes are differentially expressed in either compartment. This has provided evidence for the importance of establishing the anterior-posterior polarity within each somite, which is critical for the correct segmented pattern of the adult vertebrate body. Although all somites appear morphologically similar, fate map studies have shown that the first 4 somites do not give rise to segmented structures, in contrast to more posterior ones. Moreover, in several somitogenesis-related mutants the anterior somites are not affected while posterior somites present clear defects or do not form at all. Altogether these data suggest relevant differences between rostral and caudal somites. In order to check for molecular differences between anterior and posterior somites, we have performed a detailed expression pattern analysis of several Notch signalling related genes. For the first time, we show that the somitic expression pattern profile is not the same along the anterior-posterior axis and that the differences are not observed always at the same somite level.

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PubMed2006

Head-tail patterning of the vertebrate embryo: one, two or many unresolved problems?

When, where and how is the head-tail axis of the embryo set up during development? These are such fundamental and intensely studied questions that one might expect them to have been answered long ago. Not so; we still understand very little about the cellular or molecular mechanisms that lead to the orderly arrangement of body elements along the head-tail axis in vertebrates. In this paper, we outline some of the major outstanding problems and controversies and try to identify some reasons why it has been so difficult to resolve this important issue.

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PubMed2005

Thinking clockwise.

Throughout the Animal Kingdom, the time of embryonic development is maintained and strictly controlled. Each step of the process is successful only when it occurs at the right time and place. This raises the question: how is time controlled during embryonic development? Time control is particularly crucial during embryo segmentation processes, where the number of generated segments, as well as the time of formation of each segment, is extraordinarily constant and specific for each species. Somitogenesis is the process through which the vertebrate presomitic mesoderm is segmented along its anterior-posterior axis into round-shaped masses of epithelial cells, named somites. In the chick embryo, a new pair of somites is formed every 90 min. The discovery that this clock-like precision is dictated by the somitogenesis molecular clock constituted a landmark in the Developmental Biology field. Several genes exhibit cyclic gene expression in the embryo presomitic mesoderm from which the somites arise, presenting a 90 min oscillation period, the time required to form a pair of somites. The combined levels of dynamic gene expression throughout the presomitic mesoderm enable cells to acquire positional information, thus giving them a notion of time. Anterior-posterior patterning of the vertebrate nervous system also involves partition into discrete territories. This is particularly evident in the hindbrain where overt segmentation occurs. Nevertheless, little is known about the segmentation genes and mechanisms that may be involved. This paper intends to describe the molecular clock associated with vertebrate somitogenesis, suggesting that it may be operating in many other patterning processes.

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PubMed2005

terra is a left-right asymmetry gene required for left-right synchronization of the segmentation clock.

To establish the vertebrate body plan, it is fundamental to create left-right asymmetry in the lateral-plate mesoderm to correctly position the organs. However, it is also crucial to maintain symmetry between the left and the right sides of the presomitic mesoderm, ensuring the allocation of symmetrical body structures, such as the axial skeleton and skeletal muscles. Here, we show that terra is an early left-sided expressed gene that links left-right patterning with bilateral synchronization of the segmentation clock.

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PubMed2005

Running after the clock.

The way we currently understand vertebrate development is undoubtedly associated with the research undertaken at the "Institut d'Embryologie Cellulaire et Moleculaire" at Nogent-sur-Marne during the last decades. Working in this Institute has been a privilege for many junior and senior researchers. Eight years ago, in this stimulating environment, an exciting observation followed by a series of revealing experiments gave rise to a novel field of research. This study provided evidence for the existence of a molecular clock underlying chick somite formation. In this review, we focus on the cascade of studies that have followed this discovery. Thus far, it has been demonstrated that the molecular clock is operating in several vertebrate models namely chick, mouse, zebrafish, frog and medaka, probably functioning to provide cells with multidimensional positional information. Loss and gain of function experiments and detailed gene promoter analyses have proved very useful in understanding how the clock machinery works. Recent data has also led to the fascinating hypothesis that the clock might not be an exclusive property of somitic cells, but rather a mechanism used by a wide range of embryonic tissues. Meanwhile, the clock "keeps ticking" and many questions are still waiting for an answer.

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