Cellularization of fruit fly embryos
Reconstruction of fruit fly embryos undergoing cellularization. Cellularization is used as a model to understand the regulation of cell division. The investigation of differences between wildtype (top) and mutants like drop out (bottom) will help to unravel aberrant gene function in cancer and other diseases.
photographie de Daniel Hain (Division of Cell and Developmental Biology, College of Life Sciences)
Régulation génétique lors de l’embryogenèse
Animals develop according to a programed pattern – they follow one line from head to tail, and another from back to belly. In fruit fly embryos this pattern of development is orchestrated by a protein called dorsal, which switches certain genes on and off. Dorsal levels are spread unevenly around the embryo’s girth. The amount determines which genes are expressed where, which in turn dictates the fate of new cells. This embryo cross section shows the system at work. Each colour represents a different gene. At the top, where there is least dorsal protein, a gene called dpp (stained yellow) is turned on. At the bottom, high concentrations of dorsal switch on another gene (red). So this fluorescent pinwheel helps scientists understand how the right sorts of cells end up in the right place.
The term stem cell was first used in the 19th century to describe the Darwin-esque evolution of multicellular organisms over millions of years. Today the term is used to reflect the evolutionary-like moulding that transforms a naïve cell into a mature committed specialist in a matter of days. Stem cells respond to chemical signals in their immediate environment prompting them to mature or differentiate, into specialised cells across our bodies. Organs can avail of part-mature stem cells locally to repair damaged tissue. This ball of neural stem cells (a neurosphere, with its DNA stained blue) has received the chemical cue to differentiate into neurons. After 45 days, the newly-transformed neurons (stained red) branch out in all directions. One day soon stem cell therapy could help reverse the damage done by Parkinson’s or Alzheimer’s.
source : BPOD,
Embryogenèse du Cerveau antérieur de souris (9 jours post-fécondation)
Anterior development during early mouse embryogenesis - a scanning electron micrograph of the frontal view of a normal mouse embryo at nine days post fertilization.
Image Credit: Kenichiro Taniguchi and David Wotton (University of Virginia).
source : PLoS Genetics February 2012
Tortue siamoise / Two-headed tortoise
Une tortue des steppes à deux têtes et six pattes est exposée au musée des sciences naturelles à Kiev. “Ce n’est pas vraiment une tortue à deux têtes au sens strict du terme, mais plutôt deux tortues siamoises”, a expliqué Iouri Jouravliov, un zoologue de la société Ekzoland, qui a organisé l’exposition. L’animal, âgé de 5 ans a deux têtes, deux coeurs, quatre pattes avant, mais deux arrière et un seul intestin”.Les deux têtes ont des caractères différents même dans leurs préférences alimentaires. Celle à gauche, dominante et plus active, “préfère la nourriture verte, l’autre, des produits aux couleurs plus chaudes: carottes, fleurs de pissenlit”, a expliqué le zoologue.
A two-headed Central Asian tortoise has gone on show at the natural science museum in Kiev where visitors will be able to observe the different eating habits of each head over the next two months. “Strictly speaking it isn’t a tortoise with two heads, but rather two conjoined tortoises,” Yuri Yuravliov, a zoologist, told AFP. “The female has two heads, two hearts, four front legs, but only two hind ones, and one intestine,” he explained. The five-year-old tortoise has a heart-shaped shell, about a dozen centimetres (4.7 inches) in width, according to an AFP journalist. The two heads are quite different, even in their feeding habits. The left one is more dominant and active, “prefers green food, while the other prefers more brightly-coloured food — carrots and dandelion flowers,” said Yuravliov. The tortoise, a species that can live 50 to 60 years, was kept from birth by a Ukrainian in his home, he said. “Animals with this type of pathology are only rarely born and don’t survive in natural condition.”
A 5 year old steppe turtle with two heads and six paws is displayed as part of an exhibition at the Science History Museum in Kiev on Friday. The Ukrainian born reptile, on display at the museum, has a heart-shaped shell, two hearts but only one intestine, organisers said.
source : Reuters