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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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The World Health Organization (WHO) has created a new Web site to help researchers, doctors and patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!




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Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development


Why some genes are frequently read more than others

DNA is folded into millions of small necklaces — like beads on molecular strings — called nucleosomes. These "necklaces" allow our almost two-meter long strings of DNA to fit into a nucleus only about 0.01 mm in diameter. However, these "necklaces" actually make DNA 'unreadable'. Nucleosomes need to be temporarily "unwound" to allow genes to be copied or "read" - before a gene can produce a protein.

Wikipedia: "Gene expression is the transcription of DNA into messenger RNA using RNA polymerase. Messenger RNA then translates DNA into protein using ribosomes."

How cells ensure access to 'promoter' DNA — regions where gene transcription begins — is still not well understood. Consequently, researchers are always studying how the expression of proteins occur.

Researchers from the University of Geneva (UNIGE) and the Ecole polytechnique fédérale de Lausanne (EPFL), Switzerland, study mechanisms that control nucleosomes and then how nucleosomes affect gene expression - or how DNA becomes a protein.

How can about two meters of linear DNA contained in a mammalian cell fit into a nucleus of roughly 0.01 mm diameter? With the help of nucleosomes — the basic units made from proteins that wind a segment of DNA.

When a particular gene needs to be transcribed ("read") to create a new protein, its promoter region must be unwrapped from the nucleosome in order to be accessible to factors in the cell that initiate the transcription process.

In their research, UNIGE and EPFL researchers discovered all promoter regions can be of two distinct types – dependent on nucleosome stability.

(1) One type are the dynamic, unstable nucleosomes found in highly expressed genes — genes involved in cell growth and division.

(2) The other type contains stable nucleosomes located in less frequently expressed genes.

The interplay of these two regions is described in their work published in the journal Molecular Cell.

"It is important to understand how nucleosomes are moved, ejected or restructured, as this will affect the accessibility of promoter DNA — which in turn influences the expression of genes."

David Shore PhD, Professor, Department of Molecular Biology, Faculty of Science at the University of Geneva (UNIGE).

The dynamics of nucleosome formation and positioning in promoter regions may help us understand why some genes are highly expressed — like those involved in normal or malignant cell growth, while other are rarely expressed — like those created from stress-induced genes.

Collaborating with researchers at the Department of Computer Science (UNIGE) and the Swiss Institute of Bioinformatics at EPFL, David Shore's team undertook to characterize nucleosomes present in every gene promoter region of yeast DNA.

Yeast is a unicellular fungus used as a model organism because it functions in many ways like a mammalian cell. Yeast also possesses, as do human cells, 'fragile' nucleosomes. 'Fragile' because these nucleosomes don't resist certain enzymes as well as others. They were discovered by chance, and their nature and function had been elusive.

"We have revealed the existence of two types of promoters, which differ by the presence of 'fragile' nucleosomes."

Slawomir Kubik PhD, researcher at UNIGE, and first author of the study.

"The genome probably stays in a very compact state most of the time, with nucleosomes winding the DNA like a tight spring. We believe the presence of dynamic nucleosomes at highly expressed genes helps to unwind this spring rapidly and as often as necessary"

David Shore PhD.

Since many genes that contain 'fragile' nucleosomes are continuously at the affect of the availability of nutrients, a strategy to modify their stability may be to coordinate growth-related transcription.

•Yeast promoters form two groups based on the stability of their −1 nucleosome
•Distribution of two short DNA motifs is critical for promoter chromatin architecture
•Fragile nucleosomes are formed through the action of GRFs and chromatin remodelers

Previous studies indicate that eukaryotic promoters display a stereotypical chromatin landscape characterized by a well-positioned +1 nucleosome near the transcription start site and an upstream −1 nucleosome that together demarcate a nucleosome-free (or -depleted) region. Here we present evidence that there are two distinct types of promoters distinguished by the resistance of the −1 nucleosome to micrococcal nuclease digestion. These different architectures are characterized by two sequence motifs that are broadly deployed at one set of promoters where a nuclease-sensitive (“fragile”) nucleosome forms, but concentrated in a narrower, nucleosome-free region at all other promoters. The RSC nucleosome remodeler acts through the motifs to establish stable +1 and −1 nucleosome positions, while binding of a small set of general regulatory (pioneer) factors at fragile nucleosome promoters plays a key role in their destabilization. We propose that the fragile nucleosome promoter architecture is adapted for regulation of highly expressed, growth-related genes.

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Nov 9, 2015   Fetal Timeline   Maternal Timeline   News   News Archive   

Nucleosomes package DNA into a cell nucleus. Now, two "promoter" regions have been
identified that allow nucleosomes to either frequently or infrequently 'unwind.'
Image Credit: Molecular Cell











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