RESUMO
Polyadenylation, the process of eukaryotic mRNA 3' end formation, is essential for gene expression and cell viability. Polyadenylation of male germ cell mRNAs is unusual, exhibiting increased alternative polyadenylation, decreased AAUAAA polyadenylation signal use, and reduced downstream sequence element dependence. CstF-64, the RNA-binding component of the cleavage stimulation factor (CstF), interacts with pre-mRNAs at sequences downstream of the cleavage site. In mammalian testes, meiotic XY-body formation causes suppression of X-linked CstF-64 expression during pachynema. Consequently, an autosomal paralog, tauCstF-64 (gene name Cstf2t), is expressed during meiosis and subsequent haploid differentiation. Here we show that targeted disruption of Cstf2t in mice causes aberrant spermatogenesis, specifically disrupting meiotic and postmeiotic development, resulting in male infertility resembling oligoasthenoteratozoospermia. Furthermore, the Cstf2t mutant phenotype displays variable expressivity such that spermatozoa show a broad range of defects. The overall phenotype is consistent with a requirement for tauCstF-64 in spermatogenesis as indicated by the significant changes in expression of thousands of genes in testes of Cstf2t(-/-) mice as measured by microarray. Our results indicate that, although the infertility in Cstf2t(-/-) males is due to low sperm count, multiple genes controlling many aspects of germ-cell development depend on tauCstF-64 for their normal expression. Finally, these transgenic mice provide a model for the study of polyadenylation in an isolated in vivo system and highlight the role of a growing family of testis-expressed autosomal retroposed variants of X-linked genes.
Assuntos
Astenozoospermia/genética , Fator Estimulador de Clivagem/fisiologia , Poliadenilação/genética , Espermatogênese/genética , Animais , Astenozoospermia/patologia , Fator Estimulador de Clivagem/genética , Feminino , Fertilização , Infertilidade Masculina/genética , Infertilidade Masculina/patologia , Masculino , Camundongos , Camundongos Transgênicos , Fenótipo , RNA Mensageiro/análise , RNA Mensageiro/metabolismo , Contagem de Espermatozoides , Espermatozoides/patologia , Testículo/metabolismoRESUMO
A rapid expansion of new scientific information and the introduction of new technology in operative and diagnostic medicine has marked the last several decades. Medical educators, because of and parallel to these developments, initiated a search for a more effective system of presenting core material to medical students. The new educational trends, although varying somewhat from one institution to another, concentrated on the following pedagogical shifts: 1) expansion of conceptual presentation of material at the expense of detail-oriented education; 2) amplification of an integrated approach, as opposed to subject-oriented instruction; 3) scheduling of elective courses to compliment required courses in the curriculum; and 4) institution of small group instruction (i.e., problem-based learning) to actively involve students in the educational process and to develop deductive reasoning based on clinical cases. The future pedagogical system in medical schools will most likely be a combination of "classical" presentation of material combined with concept-oriented, subject-integrated and small group instruction based on either hypothetical or real clinical cases. It is imperative for the success of the new curriculum, however, that certain criteria are satisfied: 1) reorganize basic science departments to determine course ownership; 2) establish a reward system for teaching faculty; and 3) establish new course objectives.