Microbial media has undergone several changes since its inception but some key challenges remain. In recent years, there has been exploration of several alternative nutrient sources, both to cater to the specificity in requirement of growth of “fussy microorganisms” and also to reduce costs for large-scale fermentation that is required for biotechnology. Our mini-review explores these developments and also points at lacunas in the present areas of exploration, such as a lack of concerted effort in pH and osmolarity regulation. We hope that our commentary provides direction for future research in microbial media.

Zygotic genome activation (ZGA) initiates regionalized transcription underlying distinct cellular identities. ZGA is dependent upon dynamic chromatin architecture sculpted by conserved DNA-binding proteins. However, the direct mechanistic link between the onset of ZGA and the tissue-specific transcription remains unclear. Here, we have addressed the involvement of chromatin organizer Satb2 in orchestrating both processes during zebrafish embryogenesis. Integrative analysis of transcriptome, genome-wide occupancy and chromatin accessibility reveals contrasting molecular activities of maternally deposited and zygotically synthesized Satb2. Maternal Satb2 prevents premature transcription of zygotic genes by influencing the interplay between the pluripotency factors. By contrast, zygotic Satb2 activates transcription of the same group of genes during neural crest development and organogenesis. Thus, our comparative analysis of maternal versus zygotic function of Satb2 underscores how these antithetical activities are temporally coordinated and functionally implemented highlighting the evolutionary implications of the biphasic and bimodal regulation of landmark developmental transitions by a single determinant.

The Hippo signaling pathway has been shown to be involved in regulating cellular identity, cell/tissue size maintenance and mechanotransduction. The Hippo pathway consists of a kinase cascade which determines the nucleo-cytoplasmic localization of YAP in the cell. YAP is the effector protein in the Hippo pathway, which acts as a transcriptional cofactor for TEAD. Phosphorylation of YAP upon activation of the Hippo pathway prevents it from entering the nucleus and abrogates its function in the transcription of the target genes. In Cnidaria, the information on the regulatory roles of the Hippo pathway is virtually lacking. Here, we report the existence of a complete set of Hippo pathway core components in Hydra for the first time. By studying their phylogeny and domain organization, we report evolutionary conservation of the components of the Hippo pathway. Protein modelling suggested the conservation of YAP-TEAD interaction in Hydra. Further, we characterized the expression pattern of the homologs of yap, hippo, mob and sav in Hydra using whole-mount RNA in situ hybridization and report their possible role in stem cell maintenance. Immunofluorescence assay revealed that Hvul_YAP expressing cells occur in clusters in the body column and are excluded in the terminally differentiated regions. Actively proliferating cells marked by Ki67 exhibit YAP colocalization in their nuclei. Strikingly, a subset of these colocalized cells is actively recruited to the newly developing bud. Disruption of the YAP-TEAD interaction increased the budding rate indicating a critical role of YAP in regulating cell proliferation in Hydra. Collectively, we posit that the Hippo pathway is an essential signaling system in Hydra; its components are ubiquitously expressed in the Hydra body column and play a crucial role in Hydra tissue homeostasis.

No abstract

The evolution of the first body axis in the animal kingdom and its extensive ability to regenerate makesHydra, a Cnidarian, an excellent model system for understanding the underlying epigenetic mechanisms. We identify that monomethyltransferase SETD8 is critical for regeneration inHydrabecause of its conserved interaction with β-catenin to fine-tune the associated gene regulatory network. Inhibition of SETD8 activity abolishes head and foot regeneration inHydra. Furthermore, we show that H4K20me1, the histone mark imparted by SETD8, colocalizes with the transcriptional activation machinery locally at the β-catenin-bound TCF/LEF-binding sites on the promoters of head-associated genes, marking an epigenetic activation mode. In contrast, genome-wide analysis of the H4K20me1 occupancy revealed a negative correlation with transcriptional activation. We propose that H4K20me1 acts as a general repressive histone mark in Cnidaria and describe its dichotomous role in transcriptional regulation inHydra.