Differential Expression of Golgi Proteins During Spermatogenesis

Abstract

The Golgi apparatus of germ cells of the testis is involved in many cellular processes as these cells differentiate from spermatogonia into spermatozoa, a process defined as spermatogenesis. Differential expression profiles of non-Golgi proteins over the course of spermatogenesis, e.g. for flagellar formation, chromatin condensation and specific ER modifications, is well documented, however, that for Golgi proteins is largely unexplored. Here we focus on 14 Golgi proteins selected from a proteomic study of the isolated Golgi apparatus of germ cells of the adult rat testis, with two being novel Golgi proteins. Their distribution based on in situ light microscope immunocytochemical localizations of these proteins revealed unexpected differential temporal distributions during germ cell differentiation. While some proteins were selective for the Golgi apparatus of germ cells spanning the greater part of spermatogenesis, one was exclusive for spermatocytes. Others defined the Golgi apparatus of spermatids during their 19 steps of metamorphosis termed spermiogenesis, a subdivision of spermatogenesis. These included Golgi proteins expressed in early spermatids as they formed the acrosome (steps 1–7) and Golgi markers defining the postacrosome Golgi migration phase (steps 8–18). In addition, some proteins were reinstated during the last step of germ cell differentiation, i.e. step 19 spermatids, after being shut down from steps 8–18. Two of the 14 were expressed selectively at step 19, at a time when the Hermes body (cytoplasmic droplet) was being formed and when the Golgi structure is greatly altered. All of the 14 different Golgi proteins were mapped according to the more than 63 germ cells undergoing differentiation (truncated to 30) with the purpose of attempting to understand their functional significance as related to germ cell differentiation and functions. The complex differential distribution patterns of these Golgi proteins points to complex regulatory factors that are set in place to modulate their entry and exit at specific time points in germ cell differentiation to accommodate functional changes to these cells on route to becoming spermatozoa.