Dissection of the Fgf8 regulatory landscape by in vivo CRISPR-editing reveals extensive intra- and inter-enhancer redundancy.

Developmental genes are often regulated by multiple elements with overlapping activity. Yet, in most cases, the relative function of those elements and their contribution to endogenous gene expression remain poorly characterized. An example of this phenomenon is that distinct sets of enhancers have been proposed to direct Fgf8 in the limb apical ectodermal ridge and the midbrain-hindbrain boundary. Using in vivo CRISPR/Cas9 genome engineering, we functionally dissect this complex regulatory ensemble and demonstrate two distinct regulatory logics. In the apical ectodermal ridge, the control of Fgf8 expression appears distributed between different enhancers. In contrast, we find that in the midbrain-hindbrain boundary, one of the three active enhancers is essential while the other two are dispensable. We further dissect the essential midbrain-hindbrain boundary enhancer to reveal that it is also composed by a mixture of essential and dispensable modules. Cross-species transgenic analysis of this enhancer suggests that its composition may have changed in the vertebrate lineage.

Visualization of the hepatic veins: new approaches for the echocardiographer.

Visualization and cardiac Doppler interrogation of the hepatic veins has become an important and integral part of the routine echocardiographic examination. The challenge lies in adequate visualization of the hepatic veins by use of the standard subcostal approach. This article proposes alternate approaches when the standard view yields unsatisfactory visual and cardiac Doppler information.

The evaluation of the abdominal aorta: a "how-to" for cardiac sonographers.

A thorough evaluation of the abdominal aorta can be readily achieved by use of the standard views of the echocardiographic examination. The ultrasound evaluation of the abdominal aorta represents a logical extension of the standard echocardiographic examination of the adult patient. This article provides the information needed to carry out a complete ultrasound examination of the abdominal aorta including the anatomy, the vascular disease, and the steps involved in accomplishing the ultrasound examination of the abdominal aorta.

Histology of the rat embryo cultivated in vitro (18-22 somites).

When rat embryos are grown in culture, the morphological scoring system of Brown & Fabro (Teratology 1981, 24, 65-78) is usually employed at the end of culture to assess normal development and the effects of drugs and other chemicals. The morphological scoring system has proved very satisfactory, but its criteria only involves the external appearance of the embryo. It seems desirable to study also the internal anatomy of the embryo by histological methods. Thus, the object of this study was to gain data on the morphology of the main organ systems, with special attention given to the cardiovascular system during the developmental period most often employed in teratogenicity and embryotoxicity studies (day 9-10; 18-22-somites stage). The microscopic findings in this study agreed well with the morphological scoring system, with only one exception; whereas only two branchial arches were visible externally at the 18-22-somites stage, microscopy revealed that the third arch was also present.

The ultrastructure of the uterine epithelium of the pig during the estrous cycle and early pregnancy.

The ultrastructure of the endometrial epithelium of the pig was studied during the estrous cycle and early pregnancy up to implantation. Special attention was given to the luminal epithelium and morphological indications of protein synthesis. Although the general morphology of the luminal and glandular epithelia is similar (both tissues consist of secretory cells and ciliated cells at all the stages studied), it appears that the two epithelia should be considered as two functionally different units in the pre-implantation period. Morphological evidence suggests the presence of at least three different secretory products within luminal epithelial cells; they are released at different times, i.e. at estrus, between day 8 and 10 and after day 11. The glandular epithelium shows release of secretory products from day 10-11. Increasing amounts of glycogen were found within epithelial cells, especially in pregnant gilts from day 12. The possible significance of secretory activity of the epithelium is discussed in relation to the development of the embryos.