(T407) RAB2 IS A MAJOR SUBACROSOMAL PROTEIN OF SPERMATOZOA IMPLICATED IN ACROSOMAL BIOGENESIS.
Oko, Richard1, Mountjoy, Jeremi 1, Wu, Alexander 1, 1 Queen's University, Kingston, ON, Canada
ABSTRACT- The perinuclear theca (PT) of mammalian sperm is a unique subcellular structure encapsulating the nucleus. Compositionally the PT is made up of at least six prominent polypeptides (i.e., 60-,36-,31-,28-,25-,15-kDa) of which only two have been sequence identified as well as many less prominent ones. As an ongoing process in unveiling the protein composition of the PT, we have recently uncovered the sequence identity of the prominent 25 kDa polypeptide (PT25). Initial N-terminal sequence analysis obtained by Edman degradation suggested PT25 being a Rab2A protein. This was fortified by MALDI-TOF and Q-TOF mass spectrometric analysis and by immunoblotting with a Rab2 specific antibody. This antibody, along with one that we raised and affinity purified against isolated PT25, demonstrated, at both light and electron microscope levels, that PT25 is associated with the periphery of the acrosomic vesicle throughout the Golgi and cap phases of spermiogenesis and consequently assembled as part of the PT. This pattern of subacrosomal assembly was also observed for SubH2Bv, another prominent and exclusive subacrosomal protein, indicating a common route for subacrosomal assembly. Traditionally somatic Rab2 proteins are involved in vesicular transport between the ER and the cis side of the Golgi apparatus. Our study suggests an unprecedented direction of Rab2 mediated vesicular transport in acrosomal biogenesis, from the trans side of the Golgi apparatus to the nuclear envelope. (Supported by CIHR to RO)
KEY WORDS: perinuclear theca, subacrosomal layer, rab2, acrosomal biogenesis