Is the cadherin/catenin complex a functional unit of cell-cell actin-based adherens junctions in the rat testis?
Lee,Nikki P.Y.; Mruk,Dolores D.; Lee,William M.; Cheng,Chuen-yan
Biology of Reproduction 68(2): 489-508
Publication date: 2003
Much controversy exists regarding the presence of the cadherin/catenincomplex and its intracellular attachment site in the testis,which is the functional unit for actin-based cell-cell adherensjunctions (AJs) in multiple epithelia. Furthermore, whethergerm and Sertoli cells are equipped with the necessary AJ-associatedsignaling molecules to regulate this cadherin/catenin complexduring spermatogenesis is not known. In the present study, itwas shown that both Sertoli and germ cells indeed express N-cadherin,E-cadherin, -catenin, ß-catenin, and p120 by semiquantitativereverse transcription-polymerase chain reaction and immunoblotting.Furthermore, the assembly of AJs between Sertoli and germ cellswas associated with a transient induction in the steady-statemRNA and protein levels of cadherins and catenins. These analysesreveal, to our knowledge for the first time, that the testismay indeed be using the cadherin/catenin complex as one of thefunctional units to regulate AJ dynamics between Sertoli andgerm cells in addition to ß integrin and the nectin/afadincomplex. To further confirm the existence of such a complexbetween Sertoli and germ cells, immunoprecipitation experimentswere performed using Sertoli-germ cell lysates during AJ assembly.An anti-N-cadherin antibody can pull out ß-catenin,whereas N-cadherin can also be pulled out using an anti-ß-cateninantibody. To further expand and validate these in vitro biochemicalstudies, immunofluorescent histochemistry was performed, whichcolocalized N-cadherin and ß-catenin to the same siteof Sertoli-Sertoli and Sertoli-germ cell AJs, possibly ectoplasmicspecializations near the basal compartment, at the lower thirdof the seminiferous epithelium in vivo as well as between Sertolicells cultured in vitro. Furthermore, studies by cross-linkingusing dithiobis(succinimidylpropionate) confirmed that the cadherin/catenincomplex between Sertoli cells as well as between Sertoli andgerm cells indeed structurally linked to actin but not to vimentin(an intermediate filament protein) or to tubulin (a microtubuleprotein). These results thus unequivocally demonstrate thatthe cadherin/catenin complex, which can be up-regulated by testosterone,is indeed present between Sertoli and germ cells and is usedfor the assembly of functional AJs.