Clade-D auxin response factors regulate auxin signaling and development in the moss Physcomitrium patens

Auxin response factors (ARFs) are a family of transcription factors that are responsible for regulating gene expression in response to changes in auxin level. The analysis of ARF sequence and activity indicates that there are 2 major groups: activators and repressors. One clade of ARFs, clade-D, is sister to clade-A activating ARFs, but are unique in that they lack a DNA-binding domain. Clade-D ARFs are present in lycophytes and bryophytes but absent in other plant lineages. The transcriptional activity of clade-D ARFs, as well as how they regulate gene expression, is not well understood. Here, we report that clade-D ARFs are transcriptional activators in the model bryophyte Physcomitrium patens and have a major role in the development of this species. Δarfddub protonemata exhibit a delay in filament branching, as well as a delay in the chloronema to caulonema transition. Additionally, leafy gametophore development in Δarfddub lines lags behind wild type. We present evidence that ARFd1 interacts with activating ARFs via their PB1 domains, but not with repressing ARFs. Based on these results, we propose a model in which clade-D ARFs enhance gene expression by interacting with DNA bound clade-A ARFs. Further, we show that ARFd1 must form oligomers for full activity.

Systematic survey of the function of ROP regulators and effectors during tip growth in the moss Physcomitrella patens

Rho/Rac of plants (ROP) GTPases are plant-specific small GTPases that regulate cell morphology. ROP activity is controlled by several families of regulatory proteins. However, how these diverse regulators contribute to polarized growth remains understudied. In a system-wide approach, we used RNAi to silence each gene family of known ROP regulators in the juvenile tissues of the moss Physcomitrella patens. We found that the GTPase activating proteins, but not the ROP enhancers, are essential for tip growth. The guanine exchange factors (GEFs), which are comprised of ROPGEFs and Spikes, both contribute to growth. However, silencing Spikes results in less-polarized plants as compared to silencing ROPGEFs, suggesting that Spikes contribute more to establishing cell polarity. Silencing the single-gene family of guanine dissociation inhibitors also inhibits growth, resulting in small, unpolarized plants. In contrast, silencing the ROP effector ROP-interactive CRIB-containing (RIC) protein, which is encoded by a single gene, results in plants larger than the controls, suggesting that RIC functions to inhibit tip growth in moss. Taken together, this systematic loss-of-function survey provides insights into the function of ROP regulators during polarized growth.

Animal models for male pattern (androgenetic) alopecia

The stump-tailed macaque (Macaca arctoides) appears to be a suitable biological model for human androgenetic alopecia. The expense, danger, and low availability compromise its value but macaques currently remain the model of choice. Rodent models, both testosterone induced alopecia and various xenograft approaches, show promise for elucidating fundamental information on normal and abnormal hair growth as well as serving as models to develop new therapies to treat hair loss.

Lanceolate hair-J (lahJ): a mouse model for human hair disorders

Lanceolate hair-J (lahJ) arose spontaneously in 1994 on the DBA/1LacJ inbred background at The Jackson Laboratory. Mutant mice were runted, alopecic, and lacked vibrissae. As they aged, their skin wrinkled. Affected mice developed a noninflammatory, proliferative skin disease with follicular dystrophy. Hair fibers developed a number of abnormalities including periodic nodules along the shaft (trichorrhexis nodosa), compaction resembling trichorrhexis invaginata, spiral fractures, broken tips, and lance-shaped tips. This mutation exhibits some characteristics that resemble an autosomal recessive ichthyosiform disease that occurs in humans characterized in part by peculiar, invaginating, multinodal, hair shaft abnormalities known as Netherton's syndrome. Periodic nodules also resemble the human genetic based disease monilethrix. This autosomal recessive mouse mutation, allelic with lanceolate hair (lah), based on breeding studies, is located on mouse Chromosome 18, within a cluster of genes coding for adhesion molecules. Homozygotes for either of these allelic mouse mutations have elevated serum IgE levels, a feature also common with human Netherton's syndrome.