New insights into co-transcriptional sorting of mRNA for cytoplasmic transport during development.

During mRNA biogenesis regulation of mRNA transport and localization is an essential step. It guarantees asymmetric protein distribution across the cell necessary for specialized cellular functions, and it is a driving force for cellular differentiation and development. mRNA transport and localization depends on the interactions between cis-acting elements located across the transcript with cellular transacting factors, and emerging data supports also the involvement of structural proteins such as actin. These synergies are believed to occur co-transcriptionally when the nascent transcript is packaged into ribonucleoprotein complexes, and to determine a translationally repressed form of the mRNA only compatible with transport. The aim of this review is to highlight part of the molecular circuitry behind the decisions that control assembly of translationally repressed and de-repressed ribonucleoprotein complexes, compatible with mRNA transport or localization. I will specifically place the impact of these mechanisms in the context of spermatogenesis.