Volume 1 Number 2 2007

CONTENTS AND ABSTRACTS

Joachim Wistuba, Jan-Bernd Stukenborg, C. Marc Luetjens (Germany) Mammalian Spermatogenesis (pp 99-117)

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Invited Review: The formation of mature spermatozoa is one of the most essential functions in life. A concerted sequence of events is needed to proliferate, maintain and mature germ cells starting with spermatogonial stem cells and culminating in mature gametes. Apart from the genetic background, this process requires highly organized tissue in which the complex process of spermatogenesis is strongly regulated by hormonal interplay, differential gene expression and cell-cell communication. Although similar overall principles of spermatogenesis are found in all mammalian testes in a much conserved pattern, numerous species-specific features such as efficiency and seasonality determine differences between the various mammals. In this article we focus on morphological principles as well as on endocrine regulation and action of selected genes. Furthermore we report on recent experiments addressing the fate and physiology of spermatogonial stem cells, testis biology and development of the germ line and the somatic part of the testis by germ line transplantation and in vitro approaches.

Q. Richard Lu, Veerakumar Balasubramaniyan, Raniero L. Peru (USA) Oligodendrocyte Myelination in the Mammalian CNS (pp 118-129)

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Invited Review: Oligodendrocyte myelination is essential for the proper function of the mammalian central nervous system. The generation of myelinating oligodendrocytes is regulated by complex but coordinated signals during CNS development. Recent discoveries of critical transcriptional regulators for oligodendrocyte differentiation and axonal signals for myelin sheath production have significantly advanced our understanding of the molecular mechanisms governing oligodendrocyte myelinogenesis. This review highlights current perspectives on the origin of oligodendrocytes and the intrinsic and extrinsic regulation of oligodendrocyte differentiation and myelinogenesis. Potential implications of myelin in health and disease are also explored.

Takashi Moriguchi (USA/Japan), Kim-Chew Lim, James Douglas Engel (USA) Transcription Factor Networks Specify Sympathetic and Adrenal Chromaffin Cell Differentiation (pp 130-135)

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Invited Mini-Review: The identification of mechanisms leading to the restriction of lineage potential and cell fate specification of multipotential progenitor cells falls within the purview of the developmental biologist. In specific, neural crest (NC) cell differentiation has long been a favored model process to examine how environmental cues cooperate with cell intrinsic factors to specify the birth of multiple cell lineages, including sympathetic and adrenal chromaffin (SA) cells. Over the years, a handful of genes (MASH-1, Phox2a/b, Hand2, GATA-2/3) have been identified that, when their expression patterns are perturbed, lead to a variable degree of disruption in SA cell development, function and tissue-specific gene expression profiles. These genes have historically been thought to act in a monotonous, linear fashion (e.g. gene product A regulates gene B, whose product in turn regulates gene C). Recent genetic studies in mice and other model organisms provide substantial evidence to indicate that these regulatory effectors may interact in a non-linear, self-sustaining feedback network. This review summarizes our current knowledge of the five principal players that partake in the transcriptional regulatory circuitry that is employed during SA cell development.

Viviana Pisa, Silvia Gigliotti, Franco Graziani, Arturo C. Verrotti (Italy) Molecular Mechanisms of Metazoan Oocyte Development (pp 136-146)

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Invited Review: The gametes are responsible for passing all the genetic information from one generation to another, giving rise to all the tissues in a developing animal, and ultimately guaranteeing the survival of species. The formation of germ-line stem cells occurs during early development in all animals. The differentiation of these pluripotent cells into mature gametes provides a continuous supply of sperms and eggs during adult life. Many aspects of germ-line development are conserved across species. For example, in most metazoans, female primordial germ cells (PGCs) migrate from an extragonadal site of origin to reach the somatic gonad and to produce oocytes. After a mitotic proliferative stage, the primary oocytes enter meiosis. In most animal species this process is arrested during prophase, and is completed only in response to intercellular signaling or fertilization, which trigger oocyte meiotic maturation. After the arrest, the oocyte synthesizes and stores a large amount of mRNAs that will be translated only during re-entry into the meiotic division both to promote oocyte maturation and early embryonic development. Translational control is obtained through a complex regulation carried out by different but highly conserved molecular mechanisms. Here we review the basic principles that underlie oocyte development, focusing on analogies and differences among the main model organisms.

Melissa A. Wright, Angeles B. Ribera (USA) Studying Electrical Activity in Development: Challenges and Solutions Using the Zebrafish Model (pp 147-157)

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Invited Mini-Review: Many developmental regulators play multiple and varied roles throughout development and during the adult life of the organism. Recent studies suggest that electrical activity may similarly orchestrate a wide variety of developmental processes in addition to its classic role in regulating function of the mature nervous system. Studies utilizing several model systems indicate electrical activity is an important regulator of neuronal differentiation, neurite outgrowth, axon pathfinding, cell adhesion molecule expression, myelination, synapse stability, and cell death or survival decisions. However, very little is known regarding the mechanisms by which precise patterns of electrical activity are transduced into signals which can produce long-lasting effects on development. The study of electrical activity as a developmental regulator is a new field and poses many technical challenges. These challenges include observing and manipulating endogenous patterns of electrical activity in living, developing embryos, and evaluating the effects of altered activity patterns on the embryonic nervous system. The rise of the zebrafish as a model organism for developmental studies provides many strategies to overcome these challenges and has led to valuable insights into electrical regulation of development.