SDB 2011: Stem cells in the morning

Here we go, I’m attending the West Coast Regional Meeting of the Society for Developmental Biology, and I’ll be intermittently dumping my notes onto the web, so that’s what you’ll be getting today — my sometimes cryptic impressions of a series of developmental biology talks.

This is the early morning session. It’s late in the day for this Minnesotan, though…but beware, that just means I may start flagging this afternoon.

08:30-10:00 Session 1: Stem Cells in Development and Regeneration (Chair: Monika Ward [Univ. Hawaii])

Hey, speakers get lei’ed at the start of their talk! I guess I really am in Hawaii.

  08:30-09:00 Venugopala Reddy Gonehal (UC Riverside) “Systems level dynamics of cell interactions in plant stem cell niches: Live imaging and microgenomics”

Looking at shoot apical meristems and plant stem cells in Arabidopsis. Very cool time-lapse of plant meristems. Cell cycle length of 70-80 hours! Ouch. But still…lovely fluorescent markers of various stem cell niches, and they can examin stecell dynamics in mutants. They are using experimental data as input to mathematical models that they test in simulations. Looked at two mutants: clavata3, a secreted peptide, that leads to over-expansion of stem cells, and wuschel, a homeodomain containing trancription factor, that leads to an absence of stem cells. Increasing wuschel levels leads to expansion of the stem cell domain; using chip assays, they have worked out the response genes in this pathway…and they’re more transcription factors. 

One weird surprise: a gradient of a diffusible transcription factor that moves through plasmdesmata to induce up regulation. I guess it’s a plant thing. I spend too much time in just animal models.

Reddy’s models (shown in some very pretty simulations) can account for the generation of the patterns of gene activity in the meristem, and also accurately respond to mutations in the same way that the live tissue does.

  09:00-09:20 Kate Lynn Jaremko (Graduate student, Univ. Hawaii) “Regulation of developmental competence and commitment during endoderm and neuroectoderm differentiation in human embryonic stem cells”

Looking for ways to induce ectoderm and endoderm differentiation in hESCs, using activin signalling.  She’s giving a nice clear introduction to the concepts of competency and specificity in development. Low levels of activin signaling are required to maintain pluripotency; inhibiting activin promotes  ectoderm differentiation. experiments involve specifically timed exposures to activin or activin inhibitors , followed by examination for markers for differentiation. 

This is straightforward modern developmental biology: tinker with th molecular inputs, look at the molecular outputs, and figure out effective ways to nudge the development of a cell in a direction you desire.

  09:20-09:40 Jonathan M. Riel (Graduate student, Univ. Hawaii) “Functional deficiency of the mouse Y gene Sly leads to sperm DNA damage and abnormal chromatin packaging”

mouse has 50 copies of Rbmyf1a1 on the Y chromosome. They’re  working with a strain of mice with reduced fertility, using ICSI to get progeny. They noticed a significant difference in fertility with sperm from epididymis vs. Testis in mice with deficiencies in NPYq — traced to problems in protamine processing, suggesting that there is an NPYq gene involved in packaging and maintaining sperm DNA. Loss of the sly gene leads to abnormal sperm heads, and this work tests whether it is specifically an sly deficiency that leads to poor sperm maintenance in their mice. Loss of sly leads to a loss of membrane integrity and slightly to severely decondensed DNA condensation.

Conclusion: sly is involved in DNA packaging in spermatogenesis. Ok, I’ll believe him.

  09:40-10:00 Catherine D. McCusker (Postdoc, UC Irvine) “Insights into the establishment of positional information in the limb blastema”

Limb regeneration requires interaction with nerves — they can even induce blastemas by routing a nerve to a wound site, although it won’t regenerate into a new limb. That also requires positional information in the epidermis. The standard model invokes gradual specification by a progress zone in th egrowing limb bud. An alternative is that the full range of proximodistal morphologies are pre specified in the early limb bud.  Pre specification supported by transplant experiments that seemed to show that zones of the blastema had limited developmental potential. Distal blastemas should only be able to make distal tissues, however, new experiments with better markers show that transplanted blastemas can regenerate more proximal tissues. Thes new results suggest that the blastema is NOT pre-specified.

The basal region of the blastema is committed, and transplants will induce duplicated proximal structures.  Apical region of the early blastema does the same thing.  The new model is one of progressive specification of basal cells while apical cells are more plastic — a hybrid of the progress zone model and the pre specification model.

Talk also had pretty picture of lovely stained regenerating limbs. I’m a sucker for nice morphology.