Tau, the Neuronal Heat-Stable Microtubule-Associated Protein, is also Present in the Cross-Linked Microtubule Network of the Testicular Spermatid Manchette1

Abstract

The seminiferous tubule of the testis contains a rich variety of microtubule networks and of microtubule-associated proteins (MAPs). Tau is a heat-stable MAP previously believed to be limited in its expression in mammals to the nervous system. We have identified tau in rat and bovine testis, a unique non-neuronal location, using biochemical, molecular, and immunologic approaches. SDS-PAGE of ammonium sulfate-fractionated, testis heat-stable MAPs resulted in an enrichment of bands that comigrated with rat brain tau. Only the 35-45% precipitated ammonium sulfate fraction induced microtubule assembly. Immunoblotting with monoclonal anti-tau antibodies demonstrated tau immunoreactivity in these testis MAP preparations. Northern analysis of total rat testis RNA demonstrated a 1.7-kb band that hybridized with a 51-nucleotide oligomer complementary to a conserved portion of the tau transcript. This 51-mer identified a similar 1.7-kb minor band and an additional 6-kb major band in Northern analysis of total rat brain RNA. Finally, in the bull testis, immunohistochemistry localized tau to the spermatid manchette, a transient, cross-linked microtubule network of unknown function. As spermatid elongation begins, the manchette forms a sheath around the posterior aspect of the nucleus, but, by the completion of nuclear condensation, the manchette is largely disassembled. Tau most likely plays a structural role in the manchette; however, tau immunoreactivity also was observed in late stage I spermatids prior to manchette formation, suggesting that tau may serve a function in manchette assembly.

Cre recombinase specificity defined by the tau locus

“…This expression gives reasons for the early Cre excision we observed both in the crosses of tau::Cre with previously characterized reporter lines and in embryos derived from the double transgenic tau::Cre;Z/EG (C4) ES cells. Expression of Tau in the sperm, in fact, has previously been reported (Ashman et al, 1992), and tau mRNA has been previously cloned from the blastocyst stage embryo (Lennon, 1999). Our RT-PCR results were in accordance with these reports.…”

Testis/brain RNA-binding protein attaches translationally repressed and transported mRNAs to microtubules.

“…At lower centrifugation speeds, significant amounts of TB-RBP remain in the supernatant. Several reports have suggested the presence of novel tubulins and unique MT structures in male germ cells (29,30), variations in concentrations of MT-associated proteins have been reported to alter properties of brain MTs (31), and different neuronal populations show different susceptibilities to colchicine (32).…”

Expression of PP2A B regulatory subunit β isotype in rat testis

“…located in both neuronal axons and the manchett of the elongated spermatid [22]. Tau protein has been reported to be phosphorylated at serine/ threonine residues [33] and dephosphorylated by PP2A [34] in vitro.…”