L'Expressió al testicle de la proteïna transportadora d'esteroides sexuals humana (SHBG) té lloc a les cèl·lules germinals i no a les cèl·lules de Sertoli

The human sex hormone binding globulin (SHBG) gene contains at least two transcription units. A 4.3 kb human SHBG transcription unit encodes the precursor polypeptide, which is
processed and secreted by hepatocytes as plasma SHBG. The proximal promoter of this transcription
unit differs from the corresponding sequence in other mammals, in which it is also
expressed in Sertoli cells. In particular, its proximal promoter sequence contains a binding-site
for USF transcription factors that represses its activity in Sertoli cells. Although human SHBG
is not expressed in Sertoli cells, human SHBG transcripts containing an alternative exon 1 sequence
are present in testicular germ cells. These are the products of an ~8 kb human SHBG
transcription unit, and they appear to encode an SHBG isoform that is 4-5 kDa smaller than
plasma SHBG. This sperm SHBG isoform accumulates between the outer acrosomal membrane
and the sperm plasma membrane, and it is released during the capacitation reaction. These remarkable
differences in the expression of human SHBG in the testis, when compared to other
mammals, force us to reconsider the functional significance of SHBG expression in the testis
in relation to male reproduction.