No abstract

The Müllerian ducts are part of the embryonic urogenital system. They give rise to mature structures that serve a critical function in the transport and development of the oocyte and/or embryo. In most vertebrates, both sexes initially develop Müllerian ducts during embryogenesis, but they regress in males under the influence of testis-derived Anti-Müllerian Hormone (AMH). A number of regulatory factors have been shown to be essential for proper duct development, including Bmp and Wnt signaling molecules, together with homeodomain transcription factors such as PAX2 and LIM1. Later in development, the fate of the ducts diverges between males and females and is regulated by AMH and Wnt signaling molecules (duct regression in males) and Hox genes (duct patterning in females). Most of the genes and molecular pathways known to be involved in Müllerian duct development have been elucidated through animal models, namely, the mouse and chicken. In addition, genetic analysis of humans with reproductive tract disorders has further defined molecular mechanisms of duct formation and differentiation. However, despite our current understanding of Müllerian duct development, some questions remain to be answered at the molecular genetic level. This article is categorized under: Early Embryonic Development > Development to the Basic Body Plan.

The ratites are a distinctive clade of flightless birds, typified by the emu and ostrich that have acquired a range of unique anatomical characteristics since diverging from basal Aves at least 100 million years ago. The emu possesses a vestigial wing with a single digit and greatly reduced forelimb musculature. However, the embryological basis of wing reduction and other anatomical changes associated with loss of flight are unclear. Here we report a previously unknown co-option of the cardiac transcription factor Nkx2.5 to the forelimb in the emu embryo, but not in ostrich, or chicken and zebra finch, which have fully developed wings. Nkx2.5 is expressed in emu limb bud mesenchyme and maturing wing muscle, and mis-expression of Nkx2.5 throughout the limb bud in chick results in wing reductions. We propose that Nkx2.5 functions to inhibit early limb bud expansion and later muscle growth during development of the vestigial emu wing.

Spermatogenesis is one example of a developmental process which requires tight control of gene expression to achieve normal growth and sustain function. This review is based on the principle that events in spermatogenesis are controlled by changes in the distribution of proteins between the nuclear and cytoplasmic compartments. Through analysis of the regulated production of nucleocytoplasmic transport machinery in mammalian spermatogenesis, this review addresses the concept that access to the nucleus is tightly controlled to enable and prevent differentiation. A broad review of nuclear transport components is presented, outlining the different categories of machinery required for import, export and non-nuclear functions. In addition, the complexity of nomenclature is addressed by the provision of a concise yet comprehensive listing of information that will aid in comparative studies of different transport proteins and the genes which encode them. We review a suite of existing transcriptional analyses which identify common and distinct patterns of transport machinery expression, showing how these can be linked with key events in spermatogenic development. The additional importance of this for human fertility is considered, in light of data that identify which importin and nuclear transport machinery components are present in testicular cancer specimens, while also providing an indication of how their presence (and absence) may be considered as potential mediators of oncogenesis. This article is part of a Special Issue entitled: Regulation of Signaling and Cellular Fate through Modulation of Nuclear Protein Import.