Spnr, a murine RNA-binding protein that is localized to cytoplasmic microtubules.

Abstract

Abstract. Previous studies in transgenic mice have established the importance of the 3' untranslated region (UTR) of the spermatid-specific protamine-1 (Prm-1) mRNA in its translational control during male germ cell development. To clone genes that mediate the translational repression or activation of the Prm-1 mRNA, we screened cDNA expression libraries made with RNA from pachytene spermatocytes and round spermatids, with an RNA probe corresponding to the 3' UTR of Prm-1. We obtained six independent clones that encode Spnr, a spermatid perinuclear RNAbinding protein. Spnr is a 71-kD protein that contains two previously described RNA binding domains. The Spnr mRNA is expressed at high levels in the testis, ovary, and brain, and is present in multiple forms in those tissues. Immunolocalization of the Spnr protein within the testis shows that it is expressed exclusively in postmeiotic germ cells and that it is localized to the manchette, a spermatid-specific microtubular array. Although the Spnr protein is expressed too late to be directly involved in the translational repression of Prm-1 specifically, we suggest that the Spnr protein may be involved in other aspects of spermatid RNA metabolism, such as RNA transport or translational activation.

Cloning and characterization of the mouse Interleukin Enhancer Binding Factor 3 ( Ilf3 ) homolog in a screen for RNA binding proteins

“…Immunocytohistochemical experiments on adult mouse male testes with the ILF3 antiserum detect expression of the protein in spermatocytes and early haploid spermatids, cells that do not express the Prm1 gene (unpublished data). Additionally, four of the five cDNAs identified in this expression cloning screen encode proteins that contain the dsRBM, a motif that binds double-stranded RNA or single-stranded RNA with structure (Lee et al 1996;Schumacher et al 1995aSchumacher et al , 1995b. While the Prm1 3ЈUTR does not contain any extensive regions that could form dsRNA, there are two alternate stem loops that could theoretically form (Lee et al 1996).…”

“…Two overlapping partial cDNAs were isolated from a mouse male germ cell cDNA expression (Mitch Eddy Niehs) library probed with a radiolabeled RNA containing the Prm1 3ЈUTR (Schumacher et al 1995b). DNA sequencing and database searches led to the identification of mouse expressed sequence tags (ESTs) representing more 5Ј regions of the cDNA.…”

“…Fluorescence in situ hybridization localization of the mouse gene was performed as previously described with a Ilf3 2 kb cDNA probe (Schumacher et al 1995b).…”

Post–transcriptional control of gene expression during spermatogenesis

“…SPNR is a microtubule-RNA-binding protein that associates with the manchette in elongating and elongated spermatids and may function in translational activation of stored mRNAs. 14 …”

“…46,47 It has been suggested this structure also plays a role in overall sperm differentiation by serving as a 'track' that is utilized for the movement of organelles, vesicles and mRNPs. 14,46,48 In the molecular screen that yielded Ž Prbp, the Spnr gene spermatid perinuclear RNA-bi-.…”