The public's belief about biology.

This short review is concerned with a topic that has been neglected and is still very poorly understood: what the general public think and believe about biology (including health and medicine, and bioethics), and, in particular, about biotechnology.

Calcified abdominal aortic aneurysm in a 12-year-old boy.

The authors report a case of an idiopathic, isolated infrarenal abdominal aortic aneurysm with dense intramural calcification and sterile mesenteric lymphadenopathy in a 12-year-old boy. Aneurysmal disease in the pediatric population is very uncommon. The majority of previously reported cases have clear associated causes, such as connective tissue disorders, infectious processes, inflammatory states, or trauma. A minority of cases have no distinguishable cause and are classified as idiopathic. Isolated abdominal aortic aneurysms are very uncommon in children, and those with densely calcified walls are rare, with only 2 case reports in the literature. The authors found no previous reports of abdominal aortic aneurysm with associated sterile mesenteric lymphadenopathy. The etiology of this patient's aneurysm remains unknown.

Branching, segmentation and the metapterygial axis: pattern versus process in the vertebrate limb.

Explanations of the patterns of vertebrate fin and limb evolution are improving as specific hypotheses based on molecular and developmental data are proposed and tested. Comparative analyses of gene expression patterns and functions in developing limbs, and morphological patterns in embryonic, adult and fossil limbs point to digit specification as a key developmental innovation associated with the origin of tetrapods. Digit development during the fin-to-limb transition involved sustained proximodistal outgrowth and a new phase of Hox gene expression in the distal fin bud. These patterning changes in the distal limb have been explained by the linked concepts of the metapterygial axis and the digital arch. These have been proposed to account for the generation of limb pattern by sequential branching and segmentation of precartilagenous elements along the proximodistal axis of the limb. While these ideas have been very fruitful, they have become increasingly difficult to reconcile with experimental and comparative studies of fin and limb development. Here we argue that limb development does not involve a branching mechanism, and reassess the concept of a metapterygial axis in limb development and evolution.

Stigma of depression--a personal view.

Depression is a serious illness of which I and other patients should not be ashamed but this is hard to avoid. The stigma of depression is different from that of other mental illnesses and largely due to the negative nature of the illness that makes depressives seem unattractive and unreliable. Self stigmatisation makes patients shameful and secretive and can prevent proper treatment. It may also cause somatisation. A major contributing factor is that depression for those who have not had it is very hard to understand and so can be seen as a sign of weakness. Openness by depressives and education in schools could help.

Hypogastric artery embolization in endovascular abdominal aortic aneurysm repair.

PURPOSE: Iliac artery anatomy is a central factor in endoluminal abdominal aortic aneurysm therapy. It serves as the conduit for graft deployment and as the region of distal graft seal. Thirty-eight percent of iliac vessels in our patients require special treatment because of aneurysms, tortuosity, or small size. Bilateral hypogastric artery exclusion has been avoided because of concerns of colorectal ischemia, hip/buttock claudication, and impotence. We suggest that elective, staged, bilateral hypogastric embolization can be performed safely with reasonably low morbidity and can expand the anatomic boundaries for stent-graft abdominal aortic aneurysm repair. METHODS: This study was performed as a retrospective chart review of patients requiring hypogastric artery embolization for endovascular repair of abdominal aortic aneurysms between June 1998 and June 2000. Patients with otherwise appropriate anatomy and common iliac artery aneurysms were informed of the option for stent-graft repair with internal iliac artery embolization with its risks of impotence, hip/buttock claudication, and bowel ischemia. Patients underwent unilateral or staged bilateral coil embolizations of their proximal hypogastric arteries with an approximate 1-week interval between procedures. Hospital and office records were reviewed; phone interviews were performed. Follow-up ranged from 1 to 12 months. RESULTS: During a 24-month period, 65 patients underwent endovascular abdominal aortic aneurysm repair; 18 patients (28%) required hypogastric artery embolization. Seven (39%) of these patients underwent bilateral embolization. There were no episodes of clinically evident bowel ischemia. Lactate levels were normal in all measured patients. Postoperative fevers (> 101.0 degrees F) were documented in 10 (56%) of 18 patients. The average white blood cell count was 12.8 x 10(9)/L (range, 8.5-22.9). There were no positive blood culture results. The return to the full preoperative diet occurred in 1 to 3 days. Hip/buttock claudication occurred in approximately 50% of patients with persistent but improved symptoms at 6 months. Eighty-seven percent of patients had preoperative erectile dysfunction. Only two patients noted worsening of erectile function postoperatively. CONCLUSIONS: Preliminary results indicate that bilateral hypogastric artery embolization can be performed, when necessary, with reasonable morbidity in patients undergoing stent-graft abdominal aortic aneurysm repair.

What is evolutionary developmental biology?

All changes in animal form and function during evolution are due to changes in their DNA. Such changes determine which proteins are made, and where and when, during embryonic development. These proteins thus control the behaviour of the cells of the embryo. In evolution, changes in organs usually involve modification of the development of existing structures--tinkering with what is already there. Good examples are the evolution of the jaws from the pharyngeal arches of jawless ancestors, and the incus and stapes of the middle ear from bones originally at the joint between upper and lower jaws. However, it is possible that new structures could develop, as has been suggested for the digits of the vertebrate limb, but the developmental mechanisms would still be similar. It is striking how conserved developmental mechanisms are in pattern formation, both with respect to the genes involved and the intercellular signals. For example, many systems use the same positional information but interpret it differently. One of the ways the developmental programmes have been changed is by gene duplication, which allows one of the two genes to diverge and take on new functions--Hox genes are an example. Another mechanism for change involves the relative growth rates of parts of a structure.

A clock and trail model for somite formation, specialization and polarization.

We present some theoretical considerations about the initial process of pre-patterning during embryonic segmentation, with particular reference to somite formation. We first suggest that the pre-pattern is a stable spatial sinusoidal (or, at least, periodic) wave. The periodic wave originates from an oscillator ("clock") in the proliferative region that gives rise to the cells. At the moment the cells leave the proliferative or "progress" zone, or somewhat later, a permanent record is made of the current state of the oscillation, which cells then keep during their pre-somitic phase, before explicit somite and somite boundary formation. Thus, a trail is left behind the progress zone in the form of a spatial sine wave. Second, we also observe that the factors involved in the progress-zone clock and its wave-like trail may form multimers, which will oscillate with higher space-time frequency and thus shorter wavelengths than the monomers. Whether or not our first suggestion is correct, this phenomenon may account for multiple wavelengths in somitogenesis, and may thus encompass somite formation, but also somite polarization (half-wavelength) into anterior and posterior halves, as well as the puzzling observation that expression of her1 in zebrafish is in primordia of alternating somites, i.e. it exhibits a 2-somite wavelength.

Small bowel necrosis associated with early postoperative jejunal tube feeding in a trauma patient.

Several investigators have reported the association of small bowel ischemia and necrosis with needle catheter jejunostomy. We report a case of small bowel necrosis with continuous jejunal tube feeding and review the pathogenesis implicated in feeding-induced bowel necrosis.

Studies on the cellular basis of morphogenesis in the sea urchin embryo. Directed movements of primary mesenchyme cells in normal and vegetalized larvae.

A time-lapse study has been made of the movements of the primary mesenchyme cells in the developing sea urchin larva. It shows that these cells move by pseudopod formation and contraction, and that a transition takes place--within a few hours--from a more or less random cluster, in the early mesenchyme blastula, to a well-organized, coherent pattern on the ectoderm of the gastrula. This organization is achieved by a striking random exploration of the wall of the larva by the pseudopods, followed by their contraction. The final pattern of the mesenchyme reflects those regions of the wall where the contacts between pseudopods and wall are most stable. The mechanism is thus one of selective fixation rather than of selective conduction. The pseudopodal contacts are seen to be continually made and broken, even when the final pattern is formed. The pseudopods of several cells may fuse to form a common pseudopod, these cells then migrating together. This is particularly evident in vegetalized larvae, but is also typical of the ventral side. Despite considerable variations in the way in which the final pattern is achieved, several main phases can be distinguished. The first is a radial displacement of the cells from the vegetal plate onto the presumptive ectoderm, followed by a phase of dispersion. The cells then gradually accumulate at a characteristic level, and form a ring. During this process, and when the ring is formed, the cells tend to accumulate in two clusters along the ring. The pseudopods of the cells in these clusters join into a cable, the end of which is highly branched; it explores the ectoderm, and extends the cell clusters to form branches from the ring. In vegetalized larvae, the pattern of distribution is simplified, but the same principles apply. It is suggested that the variations in the way in which the pattern is achieved are, in all probability, merely a reflexion of the lack of precision in the time sequence of changes in adhesive properties of the primary mesenchyme and blastocoel wall.

Vertebrate limb development and malformations.

To understand limb abnormalities it is necessary to understand how the limb develops. The limb is the organ whose development is probably best understood. The limbs develop from small protrusions (the limb buds) that arise from the body wall of the embryo. Positioning and patterning the limb involves cellular interactions both between the ectoderm surrounding the limb bud and between the mesenchymal cells that form the core of the limb bud. As the limb grows out the cells acquire a positional value that relates to their position in the bud with respect to all three axes, proximo-distal, antero-posterior, and dorso-ventral. These positional values largely determine how the cells will develop such as what sort of cartilaginous elements they will form. The positional value of the cells is acquired in the progress zone at the tip of the growing bud. The time spent in the progress zone may determine the positional values along the proximo-distal axis, that is the formation of, for example the humerus, then the radius and ulna. Loss of the progress zone due to damage to the overlying apical ridge leads to truncations, and this progress zone model can also account for the effects of thalidomide. Position along the antero-posterior axis such as the character of the digits is by a signal from the polarizing region at the posterior margin of the limb and involves the signaling protein Sonic hedgehog. A signal from the dorsal ectoderm specifies the dorso-ventral axis. Hox genes that are transcription factors are expressed both along the body axis and in a complex pattern in the limb and may record positional value. Human mutations in these genes lead to limb abnormalities. Muscle cells have a separate origin from the cartilaginous cells and those that form connective tissue and tendons, and they migrate into the bud from the somites and are patterned by the connective tissue. Cell death separates the digits.

The formation of the feather pattern in chick skin after a proportion of cells have been killed by X-irradiation.

The formation of periodic patterns is of fundamental importance in embryonic development. One of the simplest and most frequently observed patterns is the maintenance of a minimum distance between neighbouring elements, for example between teeth, hair, feathers, digits etc. Theoretical models describing these phenomena have been proposed for feather patterning. However, there has been no detailed quantitative analysis of the relationship between cell population density and feather spacing. To define the relation between these quantities and specifically to test the prediction of a mathematical model, we have examined the formation of the feather pattern after varying proportions of the dermal cells have been killed by X-irradiation. It is known that the development of a feather primordium is normally associated with an increase in cell population density in the dermis. Using X-ray irradiation of the skin in vivo and in vitro, we show that the relation between cell population density and spacing of feather primordia indicates the importance of a threshold number of cells for feather patterning. Moreover, there is a prima facie case for supposing that X-rays act on feather spacing system, reducing the ability of dermal cells to prevent spreading of the pattern. Thus, X-irradiation may have a secondary effect on the spacing of primordia rather than, or as well as, affecting the mechanisms that determine their primary positions.