Developmental expression of sulfated glycoprotein-2 in the epididymis of the rat.
BACKGROUND
Sulfated glycoprotein-2 (SGP-2), also designated as clusterin, is a protein secreted by the epididymis and which binds to spermatozoa. In adult rats it is secreted at high levels by principal cells of the distal initial segment, intermediate zone and caput epididymidis, and at relatively lower levels by principal cells of the corpus and cauda epididymidis. The objective of this study was to correlate the developmental events in the maturation of the epididymis with the timing of SGP-2 expression in order to evaluate the testicular or epididymal factors which may regulate it.


METHODS
Our approach was to follow and compare the developmental expression of SGP-2 by immunocytochemistry in normal untreated control rats and rats whose efferent ducts were ligated on day 15 and examined at different postnatal ages thereafter.


RESULTS
In control animals, SGP-2 expression in principal cells of the distal initial segment, intermediate zone, and caput and distal cauda epididymidis, as characterized in normal 90-day-old adult animals, was attained between postnatal days 39 and 49. However, only by postnatal day 56 did SGP-2 display in the corpus and proximal cauda the characteristic secretory pattern found in adult rats. In contrast, in efferent duct ligated rats examined at postnatal day 64, SGP-2 was absent in principal cells of the corpus and proximal cauda epididymidis but continued to be secreted by the distal initial segment, intermediate zone, and caput and distal cauda epididymidis. Furthermore, unlike the case in control rats, SGP-2 was secreted at high levels by the principal cells of the proximal initial segment. Thus during normal postnatal development, in the proximal initial segment, the production of SGP-2 is suppressed by luminal factors originating from the testis, while in the distal initial segment, intermediate zone, and caput epididymidis, it is unaffected by these factors. On the other hand, the production of SGP-2 in the corpus and proximal region of the cauda epididymidis is normally stimulated by luminal factors originating from the testis, while in the distal cauda, it is unaffected by these factors.


CONCLUSIONS
Our results thus show a differential regulation of SGP-2 expression in principal cells of the proximal versus distal regions of the epididymis and even within subdivisions of each region. In some regions of the epididymis, SGP-2 production appears to be unaffected by luminal factors originating from the testis, while in other regions it is either inhibited or stimulated by these factors.
Hermo
L
L
Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
Barin
K
K
Oko
R
R
D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation; D051152:Clusterin; D004822:Epididymis / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D004847:Epithelial Cells; D006023:Glycoproteins / Q000032:analysis / Q000096:biosynthesis*; D007150:Immunohistochemistry; D008297:Male; D018832:Molecular Chaperones; D051381:Rats; D017207:Rats, Sprague-Dawley
D051152:Clusterin; D006023:Glycoproteins; D018832:Molecular Chaperones