Morphometric Studies Of The Glomerulus In Developing Mice

Objective: Glomerulus is the filtration unit of the kidney.The number of glomerulus and the proper morphogenesis of the capillary loop has a direct effect on the filtering function of the adult kidney and the progression of glomerular disease.In addition,several studies have been demonstrated a link between nephron endowments and the occurrence of postnatal cardiovascular disease.Nephrons are induced by ureteric bud tips in the nephrogenic zone.Therefore,the number of ureteric bud tips in the nephrogenic zone reflects the amount of nephrons.The termination of ureteric bud tips formation marks the cessation of nephron development.Few comprehensive studies on glomerulus and its environment have been reported,a quantitative morphological data describing it is currently not available.Based on the regularity of kidney morphogenesis,present study explored the morphological parameters of the nephrogenic zone,capillary loop stage glomerulus(capG),and ureteric bud tips of mice at various developmental time points by using immunohistochemical staining.Endothelial cells were labeled by CD34,and ureteric bud tips were marked with Claudin7.Methods: The kidneys were obtained from mice at different developing time points,six mice in each group,then prepared for paraffin sections and resin ultra-thin sections.The glomerulus was observed using a light microscope and an electron microscope.Simultaneously,thickness of nephrogenic zone and renal cortex,distance between ureteric bud tips,the volume density of CD34 positive exprssion in glomeruli and the volume density of glomerulus in renal cortex were measured using a combination of immunohistochemical staining and unbiased stereology.Results1.The thickness of the nephrogenic zone gradually decreased from(60±7)?m at embryonic day 14.5(E14.5),and disappeared at postnatal day 5(P5).The renal cortex showed a significant increase in thickness,which rapidly increased from(167±15)?m at E15.5 to(411±41)?m at E17.5 within 2 days,and then grow slowly until the completion of the kidney development.2.The distance between ureteric bud tips in embryonic mice decreased from(95±27)?m at E14.5 to(80±22)?m at E16.5,and finally to(52±8)?m at E18.5.3.The capG was divided into early,middle,and late phases,and middle phase capG was subdivided into early-middle and late-middle phases,according to the morphology of developing glomeruli and the arrangement of podocytes.As results,the volume density of capillary loops in early phase capG cannot be measured due to the complex“glomerular” shape.The volume density of capillary loops was increased from (35.95±6.45)(4)in the early-middle phase capG,to(58.36±6.30)(4)in the late-middle phase cap G,and to(79.89±5.21)(4)in the late phase capG,compared to(93.61±1.96)% in the mature glomerulus(postnatal day 40).Furthermore,the volume density of capillary loops remained constant during the same stages,although at various developmental time points.However,there was no significant difference in the volume density of glomerulus in the cortex at different time point,which was about(5.91±2.74)(4).Conclusion1.The distance between the ureteric bud tips changed from long to short,suggesting the branch differentiation are active in the late embryonic stage.It indicated that the number of induced nephrons reaches its peak at this stage,which is also consistent with the change in the thickness of the nephrogenic zone.2.The volume density of capillary loops showed a significant increase with the kidney development.These results provide a descriptive and reliable parameter for the evaluation of glomerular development.