Embryonic expression patterns of Hox genes in the oligochaete annelid Tubifex tubifex.

We have cloned and characterized the expression of seven Hox genes (designated Ttu-lab, Ttu-Dfd, Ttu-Scr1, Ttu-Scr2, Ttu-Lox5, Ttu-Lox4 and Ttu-Lox2) from the oligochaete annelid Tubifex tubifex. RT-PCR analyses show that except for Ttu-Lox4 and Ttu-Lox2 which begin expression as early as cleavage stages, Tubifex Hox genes are expressed during stages 13-18 when embryos undergo germ band formation, segmentation and body elongation. In terms of combination of tissues (or organs) exhibiting positive cells, the Tubifex Hox genes examined in this study are classified into three groups.

Telomere distribution pattern and synapsis initiation during spermatogenesis in zebrafish.

Background: Telomeres are located at ends of eukaryotic chromosomes and can affect proper chromosomal positioning. During spermatogenesis, the appropriate dynamics and behavior of chromosomes is crucial to generate haploid cells through meiosis. Here, we describe telomere distribution patterns during spermatogenesis in zebrafish, especially during meiotic prophase I, using fluorescence in situ hybridization.

Production of zebrafish offspring from cultured spermatogonial stem cells.

Germ-line stem cells have the potential to be a very powerful tool for modifying the genetic information of individual animals. As a first step to use spermatogonial stem cells (SSCs) to enable genetic modification, we here describe effective long-term culture conditions for propagating zebrafish SSCs and for the production of offspring from these cultured SSCs after their differentiation into sperm in transplanted testicular cell aggregates. Dissociated testicular cells were cultured in specific medium with some modified supplements, including several mammalian growth factors.

Artificial fertilization by intracytoplasmic sperm injection in a teleost fish, the medaka (Oryzias latipes).

Intracytoplasmic sperm injection (ICSI) is a technique that has been successfully used for assisting reproduction in mammals. However, this method is still not reliable in nonmammalian species, including teleosts. We succeeded in producing medaka individuals by ICSI with a rate of 13.

Structural components of the synaptonemal complex, SYCP1 and SYCP3, in the medaka fish Oryzias latipes.

The synaptonemal complex (SC) is a meiosis-specific structure essential for synapsis of homologous chromosomes. For the first time in any non-mammalian vertebrates, we have isolated cDNA clones encoding two structural components of the SC, SYCP1 and SYCP3, in the medaka, and investigated their protein expression during gametogenesis. As in the case of mammals, medaka SYCP1 and SYCP3 are expressed solely in meiotically dividing cells.