Although mammalian polypyrimidine tract-binding (PTB) protein functions in most or all cell types to regulate a wide spectrum of transcripts, Drosophila PTB encodes an abundant male germlinespecific mRNA isoform (dmPTB) whose expression correlates with male fertility. The biological function of this isoform is unknown. Using selection-amplification, we show that mammalian and Drosophila PTB have similar RNA sequence preference, suggesting that cell-specific expression rather than unique RNA-binding properties account for the sex-specific function of dmPTB. We also show that the dmPTB protein isoform expressed in the male germline is by far the most abundant isoform, and reduction of its levels correlates with male sterility. Finally, we show that dmPTB expression is necessary for proper spermatid individualization, the terminal step necessary for production of motile sperm. Loss of dmPTB results in severe disruption of the actin cones of the spermatid individualization complex. This represents a cytological defect resulting from PTB loss. We discuss the basis for functional differences between mammalian and Drosophila PTB orthologs.individualization complex | spermatogenesis | male germline | selectionamplification | RNA binding protein R NA-binding proteins play an important role in posttranscriptional regulation. Among hundreds of known RNA-binding proteins, the biological function is known for only a few. RNAbinding proteins typically bind short, degenerate sequences, which occur frequently by chance throughout the genome and make functional analysis harder. The mammalian polypyrimidine tractbinding protein or heterogeneous nuclear ribonucleoprotein I (PTB/hnRNP I) is one of the well-studied RNA-binding proteins. The hnRNP proteins are ubiquitously expressed, associate with nascent transcripts, and play various roles in RNA metabolism. PTB is known to affect mRNA splicing, polyadenylation, translation, mRNA stability/degradation, and mRNA localization (reviewed in refs. 1 and 2).Mammalian PTB, which is considered a general splice site repressor, regulates the tissue-specific alternative splicing or localization of a wide spectrum of premRNAs (e.g., CT/CGRP α-tropomyosin, c-src, α-actinin, and fibronectin) (3-6) involving tissue-specific expression of corepressors or PTB antagonists (7). PTB contains four RNA recognition motifs (RRMs) and binds to pyrimidine-rich sequences with (short, degenerate) motifs, such as UCUUC and CUCUCU (8); RRM3 and RRM4 provide the major contribution to specific RNA recognition (9). Diverse mechanisms have been proposed for how PTB binding regulates splice site choice. These include direct competition with the splicing factor U2AF 65 (8, 10); multimerization across an exon to create a zone of silencing or cause exon looping (3, 9, 11-13); interference with exon definition (14); and competition with tissue-specific paralogs (nPTB/brPTB) (15) or with PTB antagonists (ETR-3, RBM4, and CELF) (16-18).Previously, we found that in Drosophila a major PTB transcript is male germline specifi...

Our surgical technique for splenopexy was successful and the patient returned home on postoperative day four. No significant complications occurred. This video demonstrates this technique and highlights the key steps. Splenopexy by encircling the spleen with polyglactin 910 mesh is feasible, preserves splenic function, and can be performed with standard laparoscopic equipment. Tacks or transfascial sutures are a potential option for securing mesh.

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