Advances in Anatomy Embryology and Cell Biology最新文献

The very first cell divisions in mammalian embryogenesis produce a ball of cells, each with the potential to form any cell in the developing embryo or placenta. At some point, the embryo produces enough cells that some are located on the outside of the embryo, while others are completely surrounded by other cells. It is at this point that cells undergo the very first lineage commitment event: outer cells form the trophectoderm and lose the potential to form embryonic lineages, while inner cells form the Inner Cell Mass, which retain embryonic potential. Cell identity is defined by gene expression patterns, and gene expression is largely controlled by how the DNA is packaged into chromatin. A number of protein complexes exist which are able to use the energy of ATP to remodel chromatin: that is, to alter the nucleosome topology of chromatin. Here, we summarise the evidence that chromatin remodellers play essential roles in the successful completion of preimplantation development in mammals and describe recent efforts to understand the molecular mechanisms through which chromatin remodellers facilitate the successful completion of the first cell fate decisions in mammalian embryogenesis.

In this chapter, we describe the visuotopy of the pulvinar subdivisions P1, P2, and P4. In all primates, P1 colocalizes with the chemoarchitecturally defined PI and a small portion of PL. The peripheral visual field is represented anteriorly in the medial portion of PI, while central vision is represented more posteriorly in the medial portion of PL. The vertical meridian representation is located on the lateral edge of P1, while the horizontal meridian is represented obliquely from the lateral to the medial extent of P1. The upper visual field is represented ventrally, while the lower field is located dorsally. P2 has only been described in the macaque monkey. It contains a representation of the peripheral visual field, located in its anterior portion, and of the central field, which is located in posterior PL. P4 has a complex topographic arrangement. The representation of the vertical meridian is located on the dorsal edge of P4, while the representation of the horizontal meridian divides P4 into dorsal and ventral portions.

This chapter deals with the role of the pulvinar in spatial visual attention. There are at least two aspects in which the pulvinar seems to be instrumental for selective visual processes. The first aspect concerns pulvinar connectivity pattern. The pulvinar is connected with brain regions known to be playing a role in attentional mechanisms, such as area V4, the superior colliculus (SC), and the inferior parietal cortex (IP). Additionally, the pulvinar is richly interconnected with multiple cortical areas. This enables the pulvinar to serve as a hub for brain communication, potentially gating the flow of information across different regions. The second aspect concerns neuronal circuits intrinsic to the pulvinar. We claim these circuits are subserving three basic steps regarding the allocation of spatial attention: disengaging from the current focus of attention, moving it to a new target, and engaging it at a new position.

The successful development from a single-cell zygote into a complex multicellular organism requires precise coordination of multiple cell-fate decisions. The very first of these is lineage specification into the inner cell mass (ICM) and trophectoderm (TE) during mammalian preimplantation development. In mouse embryos, transcription factors (TFs) such as Oct4, Sox2, and Nanog are enriched in cells of ICM, which gives rise to the fetus and yolk sac. Conversely, TFs such as Cdx2 and Eomes become highly upregulated in TE, which contribute to the placenta. Here, we review the current understanding of key transcriptional control mechanisms and genes responsible for these distinct differences during the first cell lineage specification. In particular, we highlight recent insights gained through advances in genome manipulation, live imaging, single-cell transcriptomics, and loss-of-function studies.

The extraembryonic endoderm is one of the first cell types specified during mammalian development. This extraembryonic lineage is known to play multiple important roles throughout mammalian development, including guiding axial patterning and inducing formation of the first blood cells during embryogenesis. Moreover, recent studies have uncovered striking conservation between mouse and human embryos during the stages when extraembryonic endoderm cells are first specified, in terms of both gene expression and morphology. Therefore, mouse embryos serve as an excellent model for understanding the pathways that maintain extraembryonic endoderm cell fate. In addition, self-renewing multipotent stem cell lines, called XEN cells, have been derived from the extraembryonic endoderm of mouse embryos. Mouse XEN cell lines provide an additional tool for understanding the basic mechanisms that contribute to maintaining lineage potential, a resource for identifying how extraembryonic ectoderm specifies fetal cell types, and serve as a paradigm for efforts to establish human equivalents. Given the potential conservation of essential extraembryonic endoderm roles, human XEN cells would provide a considerable advance. However, XEN cell lines have not yet been successfully derived from human embryos. Given the potential utility of human XEN cell lines, this chapter focuses on reviewing the mechanisms known to govern the stem cell properties of mouse XEN, in hopes of facilitating new ways to establish human XEN cell lines.

In this chapter, we discuss the poor agreement between visuotopic maps described using electrophysiological and connectivity data and the subdivisions of the pulvinar based on chemoarchitecture. We focus on the differences and similarities between New and Old World monkeys to evaluate how this agreement evolved during evolution. There is some agreement in the localization of P1, described using electrophysiological and connectivity data, and the lateral and central portions of the nucleus pulvinaris inferior (PI), defined based on chemoarchitectural criteria. Similarly, there is some colocalization between P3 and the medial portion of PI in both New and Old World monkeys. One difference between primates refers to P2, which is present in the Old World macaque monkey but absent in the New World monkeys. P4, which has not been studied in all primates, shows a partial spatial agreement with the dorsal portion of the chemoarchitecturally defined PL.

In this chapter, we compare the pattern of pulvinar immunohistochemical staining for the calcium-binding proteins calbindin and parvalbumin and for the neurofilament protein SMI-32 in macaque, capuchin, and squirrel monkeys. This group of New and Old World primates shares five similar pulvinar subdivisions: PI_P, PI_M, PI_C, PI_L, and PI_LS. In the Old World macaque monkey, the inferior-lateral pulvinar can be subdivided into the P1 and P2 fields based on its connectivity with visual area V1. On the other hand, only the P1 field and no P2 was found in the New World capuchin monkey. Notably, the similarities in chemoarchitecture contrast with the distinct connectivity patterns and the different visuotopic organizations found across the species.

The pulvinar can be subdivided into well-delimitated regions based on chemoarchitectural, cytoarchitectural, myeloarchitectural, connectivity, and electrophysiological criteria. Subdivisions of the pulvinar based on its chemoarchitectural features are the most consistently preserved across species of New and Old World monkeys. It is reasonable to speculate that the occurrence and distribution of calcium-binding proteins in the pulvinar, such as calbindin and parvalbumin, have been preserved along evolution. Therefore, they have proven to be valuable tools capable of probing the basic pulvinar scaffold across primate species. Along this review, we will provide an overview of the available data regarding the various subdivisions of the pulvinar that have been proposed based on architectural criteria such as the distribution of molecular markers, neuronal morphology, and fiber layout.

In this chapter, we discuss the types of visual receptive fields revealed by single-unit electrophysiological recordings in the pulvinar. Nearly all neurons with identifiable receptive fields responded to visual stimulation presented on the contralateral hemifield, within 25° of the fovea. The majority of the visual neurons responded to some form of moving stimulus, and some additionally exhibited direction or orientation selectivity. Most units could be driven by monocular stimulation and showed receptive fields of at least 100 square degrees in area. Finally, most of the units recorded exhibited continuous peripheral receptive fields, even though a few of them could be bilaterally activated.

In this chapter, we discuss the effects of GABA (gamma-aminobutyric acid) inactivation of the pulvinar on the electrophysiological responses to visual stimuli. A direct way to access the pulvinar-cortical interaction is to pharmacologically inactivate the pulvinar and measure the impact on cortical activity. To this aim, we have focused our efforts on recording in cortical visual area V2 while inactivating the topographically corresponding region of the pulvinar.