Essential role for the Pak4 protein kinase in extraembryonic tissue development and vessel formation

Pak4 is a member of the group B family of Pak serine/threonine kinases, originally identified as an effector protein for the Rho GTPase Cdc42. Pak4 knockout mice are embryonic lethal and do not survive past embryonic day 11.5. Previous work on Pak4 knockout mice has focused on studying the phenotype of the embryo. Abnormalities in the extraembryonic tissue, however, are common causes of early embryonic death in knockout mice. Extraembryonic tissue associated with the Pak4-null embryos was therefore examined. Abnormalities in both yolk sacs and placentas resulted when Pak4 was deleted. These included a lack of vasculature throughout the extraembryonic tissue, as well as an abnormally formed labyrinthine layer of the placenta. Interestingly, epiblast-specific deletion of Pak4 using a conditional knockout system, did not rescue the embryonic lethality. In fact, it did not even rescue the extraembryonic tissue defects. Our results suggest that the extraembryonic tissue abnormalities are secondary to defects that occur in response to epiblast abnormalities. More detailed analysis suggests that abnormalities in vasculature throughout the extraembryonic tissue and the epiblast may contribute to the death of the Pak4-null embryos.     

WJSC 6th Anniversary Special Issues（2）:Mesenchymal stem cells Mesenchymal stem cells help pancreatic islet transplantation to control type 1 diabetes

Islet cell transplantation has therapeutic potential to treat type 1 diabetes,which is characterized by autoimmune destruction of insulin-producing pancreatic isletβcells.It represents a minimal invasive approach forβcell replacement,but long-term blood control is still largely unachievable.This phenomenon can be attributed to the lack of islet vasculature and hypoxic environment in the immediate post-transplantation period that contributes to the acute loss of islets by ischemia.Moreover,graft failures continue to occur because of immunological rejection,despite the use of potent immunosuppressive agents.Mesenchymal stem cells(MSCs)have the potential to enhance islet transplantation by suppressing inflammatory damage and immune mediated rejection.In this review we discuss the impact of MSCs on islet transplantation and focus on the potential role of MSCs in protecting islet grafts from early graft failure and from autoimmune attack.     

The vascularization of the neural stalk and the pars nervosa of the hypophysis in the toad,Bufo bufo (L.) (amphibia,anura)

The angioarchitecture of the neural stalk and the encephaloposthypophysial portal system of the hypophysis of the toad, Bufo bufo (L.), was studied using three different methods. The neural stalk is mainly supplied by branches of the arteria infundibularis superficialis which form a widemeshed vascular network. Dorsally this network continues into the plexus of the pars nervosa. The vascularization of the pars nervosa is made up of the encephalo-posthypophysial portal system. This portal system consists of a hypothalamic branch (=portion), a mesencephalic and a mesencephalicbulbar branch (=portion). The hypothalamic branch was found to drain the pars ventralis of the tuber cinereum as well as more dorsal regions of the diencephalon. The mesencephalic-bulbar trunk enters the hypothalamic branch. The resulting common stem of the encephalo-posthypophysial portal vein the curves around the retroinfundibular communicating artery, crosses its ventral side and runs caudally. The secondary capillary plexus of the pars nervosa is characterized by well defined capillary plexus of the pars nervosa is characterized by well defined capillary networks which are located at the periphery of the parenchyma of the pars nervosa, thus forming a rostral, dorsal and ventro-caudal net. The central region of the parenchyma of the pars nervosa is supplied only by main branches of the encephalo-postpophysial portal vein. The venous drainage of the pars nervosa is via the vena hypophysea transversa.     

Identification and characterization of a previously undetected region between the perichondrium and periosteum of the developing avian limb

In developing long bones, the growing cartilage and bone are surrounded by the fibrous perichondrium (PC) and periosteum (PO), respectively, which provide cells for the appositional growth (i.e., growth in diameter) of these tissues. Also during the longitudinal growth of a bone, the cartilage is continuously replaced by bony tissue, giving rise to the widely held assumption that the PC concomitantly gives rise to the PO. Except for this morphological correlate, however, no evidence exists for a direct conversion of PC cells to PO cells, and our observations presented here question this assumption. Instead, we have obtained evidence suggesting that a previously undescribed region exists between the PC and PO. This region, termed the border region (BR), has several unique characteristics which distinguish it from either the PC or PO, including (1) its lack of being determined to differentiate as either cartilage or bone, (2) its ability to preferentially elicit the invasion of blood vessels, and (3) its ability to undergo preferential growth.     

Simulating complex tumor dynamics from avascular to vascular growth using a general level-set method

A comprehensive continuum model of solid tumor evolution and development is investigated in detail numerically, both under the assumption of spherical symmetry and for arbitrary two-dimensional growth. The level set approach is used to obtain solutions for a recently developed multi-cell transport model formulated as a moving boundary problem for the evolution of the tumor. The model represents both the avascular and the vascular phase of growth, and is able to simulate when the transition occurs; progressive formation of a necrotic core and a rim structure in the tumor during the avascular phase are also captured. In terms of transport processes, the interaction of the tumor with the surrounding tissue is realistically incorporated. The two-dimensional simulation results are presented for different initial configurations. The computational framework, based on a Cartesian mesh/narrow band level-set method, can be applied to similar models that require the solution of coupled advection-diffusion equations with a moving boundary inside a fixed domain. The solution algorithm is designed so that extension to three-dimensional simulations is straightforward.     

植入血管束的血管化人工神经导管对受损神经功能恢复影响的实验研究

目的:研究植入血管束的血管化人工神经导管修复SD大鼠长段坐骨神经缺损对神经功能恢复的影响。方法:将18只成年雌性SD大鼠制成14mm的大鼠坐骨神经缺损模型后,随机分为3组(每组12条神经),分别采用不同的修复方法。A组:自体神经移植组(自体组);B组:普通PGLA神经导管移植组(导管组);C组:植入自体血管束的普通PGLA神经导管移植组(血管化导管组)。观察术后大鼠后肢皮肤溃疡面积;检测术后6周、12周时步态变化和肌电图。结果:术后各组SD大鼠均出现后肢溃疡,血管化导管组SD大鼠后肢溃疡愈合较导管组早2周。血管化导管组步态检测SFI明显优于导管组,与自体神经移植组无明显差异。肌电图检测表明血管化导管组无论是神经传导速度,还是动作电位振幅均明显大于导管组(P<0.05),与自体神经移植组无明显差异(P>0.05)。结论:植入血管束的血管化人工神经导管能有效地促进受损神经的功能恢复。     

The angioarchitecture of estrous, pseudopregnant and pregnant rabbit ovary as seen by scanning electron microscopy of vascular corrosion casts

Ovarian angioarchitecture was studied by scanning electron microscopy of vascular corrosion casts in estrous, pseudopregnant (stimulated with human chorionic gonadotropin) and pregnant rabbits. In all samples, the proper ovarian branch of the ovarian artery (ramus ovaricus) entered the ovarian hilus near the caudal pole of the organ and ran parallel to the major axis of the hilus. The extraovarian venous drainage was formed by several vessels emptying into a distal large vein. The ramus ovaricus exhibited various degrees of coiling and branched in the medulla. The coiling of the ramus ovaricus and its ramifications were maintained in all samples. A venous meshwork and/or flat vein branches closely enveloped the arterial coils found in the hilus and outer medulla. At this level numerous arteriovenous contacts were demonstrated in all samples. The coiled arteries, prior to entering the ovarian cortex, supplied several small peripheral follicles which were drained by the hilar veins. In the cortex the coiled arteries branched in numerous thin, straight or slightly undulated arterioles which supplied developing estrous follicles and pseudopregnant corpora lutea. The arterioles supplying the pregnant corpora lutea were long, large and tightly spiraled. The venous drainage followed the modifications of the arterial supply. These data demonstrate that ovarian cycle and pregnancy induced significant changes in the cortical vessels, which adapted their structure to the temporary functional needs of the recruited follicles or corpora lutea. Hilar and medullary vessels have permanent structures that may represent morphological devices for (a) a continuous control of the blood flow (spiral arteries) and (b) a local recirculation of endocrine products (arteriovenous contacts) comparable to the ”countercurrent mechanism” previously shown to operate in ovaries of other species, but not yet found in rabbits. Received: 19 June 1996 / Accepted: 7 October 1996     

A vascular network closely linked to the epithelium of the urinary bladder of the rat

Summary Scanning electron microscopy was used on the mucosa of the rat urinary bladder after digestion with strong alkali and microdissection. The underside of the epithelium (and the plane of the epithelium-tunica propria interface) is not smooth but is scored by grooves-10 m wide and 3–4 m deep—connected into a fine mesh. A net of blood capillaries located in the uppermost part of the tunica propria occupies these grooves. They measure 3–9 m in diameter, are separated from the epithelium by a gap of 0.3 m, often show fenestrations, and are accompanied by numerous and extensive pericytes and by some fibroblasts. We discuss these observations in the light of current knowledge of blood flow in the bladder, contraction and distension of the bladder wall and formation of mucosal folds, transport of solutes through the epithelium, and plasma extravasation from mucosal blood vessels in neurogenic inflammation.     

Wnt-4 signaling is involved in the control of smooth muscle cell fate via Bmp-4 in the medullary stroma of the developing kidney

Wnt-4, a member of the Wnt family of secreted signaling molecules, is essential for nephrogenesis, but its expression in the presumptive medulla suggests additional developmental roles in kidney organogenesis. We demonstrate here that Wnt-4 signaling plays also a role in the determination of the fate of smooth muscle cells in the medullary stroma of the developing kidney, as a differentiation marker, smooth muscle alpha-actin (alpha-SMA), is markedly reduced in the absence of its signaling. Wnt-4 probably performs this function by activating the Bmp-4 gene encoding a known differentiation factor for smooth muscle cells, since Bmp-4 gene expression was lost in the absence of Wnt-4 while Wnt-4 signaling led to a rescue of Bmp-4 expression and induction of alpha-SMA-positive cells in vitro. Recombinant Bmp-4 similarly rescued the differentiation of alpha-SMA-expressing cells in cultured Wnt-4-deficient embryonic kidney. The lack of smooth muscle cell differentiation leads to an associated deficiency in the pericytes around the developing vessels of the Wnt-4-deficient kidney and apparently leads to a secondary defect in the maturation of the kidney vessels. Thus, besides being critical for regulating mesenchymal to epithelial transformation in the cortical region in nephrogenesis, Wnt-4 signaling regulates the fate of smooth muscle cells in the developing medullary region.