Smaug regulates germ plasm assembly and primordial germ cell number in Drosophila embryos.

During Drosophila oogenesis, the Oskar (OSK) RNA binding protein (RBP) determines the amount of germ plasm that assembles at the posterior pole of the oocyte. Here, we identify mechanisms that subsequently regulate germ plasm assembly in the early embryo. We show that the Smaug (SMG) RBP is transported into the germ plasm of the early embryo where it accumulates in the germ granules. SMG binds to and represses translation of the osk messenger RNA (mRNA) as well as the bruno 1 (bru1) mRNA, which encodes an RBP that we show promotes germ plasm production. Loss of SMG or mutation of SMG's binding sites in the osk or bru1 mRNA results in excess translation of these transcripts in the germ plasm, accumulation of excess germ plasm, and budding of excess primordial germ cells (PGCs). Therefore, SMG triggers a posttranscriptional regulatory pathway that attenuates the amount of germ plasm in embryos to modulate the number of PGCs.

The association between size and symmetry of the lumbar multifidus muscle, and injuries in adolescent rugby union players.

OBJECTIVES: This study aimed to investigate the association between size and symmetry of the lumbar multifidus muscle, and season injuries in adolescent rugby union players. DESIGN: Prospective longitudinal cohort study. SETTING: Pre-season assessment of the size (cross-sectional area) of the lumbar multifidus (L2-5) muscles using ultrasound imaging. PARTICIPANTS: Seventy-one adolescent rugby union players (aged 15-18 years). MAIN OUTCOME MEASURES: "Time-loss" injuries were recorded during the season and divided into four injury regions (head and neck, upper limb, trunk and lower limb). RESULTS: Thirty-nine injuries were recorded during the season. Players who sustained an upper limb injury during the season had smaller lumbar multifidus muscles at the L5 vertebral level (effect size = 0.7, p = 0.03) and asymmetry in muscle size at the L2 (p = 0.05) and L5 (p = 0.04) in the pre-season. There was no association between size of the lumbar multifidus muscle and other injuries (p > 0.05). CONCLUSION: Lumbar multifidus muscle size and symmetry may impact lumbopelvic control which may increase the risk of sustaining an upper limb injury during rugby union. Future research should aim to identify whether lumbar multifidus muscle size is a modifiable risk factor for rugby union injuries to guide future intervention programs.

Precise Temporal Regulation of Post-transcriptional Repressors Is Required for an Orderly Drosophila Maternal-to-Zygotic Transition.

In animal embryos, the maternal-to-zygotic transition (MZT) hands developmental control from maternal to zygotic gene products. We show that the maternal proteome represents more than half of the protein-coding capacity of Drosophila melanogaster's genome, and that 2% of this proteome is rapidly degraded during the MZT. Cleared proteins include the post-transcriptional repressors Cup, Trailer hitch (TRAL), Maternal expression at 31B (ME31B), and Smaug (SMG). Although the ubiquitin-proteasome system is necessary for clearance of these repressors, distinct E3 ligase complexes target them: the C-terminal to Lis1 Homology (CTLH) complex targets Cup, TRAL, and ME31B for degradation early in the MZT and the Skp/Cullin/F-box-containing (SCF) complex targets SMG at the end of the MZT. Deleting the C-terminal 233 amino acids of SMG abrogates F-box protein interaction and confers immunity to degradation. Persistent SMG downregulates zygotic re-expression of mRNAs whose maternal contribution is degraded by SMG. Thus, clearance of SMG permits an orderly MZT.