Role of apoptosis in the development of the ascending thin limb of
the loop of henle in the rat kidney.
Kim, Jin, Gye-Sil Lee, C. Craig Tisher, and Kirsten M. Madsen.
Department of Anatomy, Catholic University Medical College, Seoul,
Korea; and Laboratory of Experimental Morphology, Division of
Nephrology, Hypertension, and Transplantation, University of Florida,
Gainesville, FL 32610-0224, USA
APStracts 3:0112F, 1996.
At birth the rat renal papilla has the structural composition of the
mature inner stripe of the outer medulla. All loops of Henle have the
configuration of short loops, and there are no ascending thin limbs.
This study examines the role of apoptosis in the differentiation of
the loop of Henle and the development of the ascending thin limb in
the rat kidney. Kidneys of 20-day-old fetuses and 1-,3-,5-,7-,14-,
and 21-day-old pups were preserved for immunohistochemistry and
electron microscopy. Using a preembedding immunoperoxidase method,
thick ascending limbs were identified by labeling with antibodies to
the serotonin receptor, 5-HT1A, and descending thin limbs were
identified by labeling with antibodies to aquaporin 1 (AQP-1). Three
methods were used to identify apoptotic cells: 1, in situ nick end
labeling using the ApopTag kit; 2, toluidine blue staining on plastic
sections followed by etching; and 3, transmission electron
microscopy. At birth, tubules with 5-HT1A-immunoreactivity were
present throughout the renal papilla, and there were no ascending
thin limbs. From 1 to 14 days of age, staining for apoptosis was
observed in numerous cells in the 5-HT1A-positive epithelium,
beginning at the papillary tip and ascending to the border between
outer and inner medulla. This was associated with transformation from
a cuboidal to a squamous epithelium and subsequent disappearance of
5-HT1A immunostaining from the transformed cells. Electron microscopy
confirmed the presence of apoptotic cells and phagocytosed apoptotic
bodies in the thick ascending limb in the renal papilla. We conclude
that the ascending thin limb is derived from the 5-HT1A-positive
thick ascending limb by apoptotic deletion of thick ascending limb
cells and transformation of the remaining tubule cells into the 5
-HT1A-negative ascending thin limb.
Received 17 April 1996; accepted in final form 20 June 1996.
APS Manuscript Number F118-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96