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Mouse Sperm Cell-Specific DnaJ First Homologue: An Evolutionarily Conserved Protein for Spermiogenesis¹

^a Dipartimento di Medicina Sperimentale, Sez."F.BOTTAZZI," II Università di Napoli, 80138 Napoli, Italy ^b Dipartimento di Biologia "L.GORINI," Università di Milano, 20133 Milano, Italy ^c Unité INSERM 421, Faculté de Médicine, 94010 Créteil, France ^d Dipartimento di Biotecnologie e Bioscienze, Università Bicocca, Milano, Italy

Msj-1 (mouse sperm cell-specific DnaJ first homologue) is a gene specifically expressed in germ cells at haploid stages. The protein first appears in round spermatids, accumulates in the periacrosomal region of elongating spermatids, and is maintained in spermatozoa. The msj-1 expression pattern is consistent with a role for this DnaJ protein in the spermiogenesis process. In this study, we used two experimental models, the anuran amphibian Rana esculenta and the wobbler mutant mouse, to explore the role of MSJ-1 during spermatogenesis, with a focus on spermiogenesis. Mice homozygous for the recessive mutation wobbler (wr/wr), a mutation of unknown identity, produce sperm cells characterized by a missing acrosome. In Rana esculenta testis, detection of high levels of MSJ-1 protein coincided with the appearance of postmeiotic germ cells during the annual sexual cycle. Conversely, elimination of the meiotic and postmeiotic stages, through gonadotropin administration at low temperature, abolished the MSJ-1 immunoreactive signal. In 20-day-old mice, when postmeiotic germ cells appeared for the first time, MSJ-1 mRNA and protein were observed in +/+ testis but were barely detectable in wr/wr testis. In adult testis, reduced MSJ-1 protein levels were observed in both +/wr and wr/wr testis, as compared with +/+ controls. Similarly, numbers of spermatids that stained by immunofluorescence for MSJ-1 appeared to be progressively reduced in adult +/+, +/wr, and wr/wr mouse testes, respectively. Characterization of the endocrine status of wobbler testis revealed reduced transcript levels of estrogen receptor and reduced intratesticular androgen levels. However, androgen treatment did not affect MSJ-1 protein levels in either frogs or mice. In conclusion, our data in Rana esculenta and the wobbler mouse demonstrate a tight correlation between MSJ-1 protein expression and postmeiotic stages. In particular, the findings in the wobbler testis suggest a role for this protein in acrosomogenesis.

First decision: 26 July 2001.

¹ This work was supported by grants from MURST "ex40% Geremia" and 60%, the Association Française contre les Myopathies (M.P.J., S.B.) and was carried out within the CNR "Target Project on Biotechnology."

² Correspondence: Riccardo Pierantoni, Dipartimento di Medicina Sperimentale, Sez. "F.BOTTAZZI," II Università di Napoli, Via Costantinopoli 16, 80138 Napoli, Italy. FAX: 19 39 081 5667536/7500; riccardo.pierantoni{at}unina2.it

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