Episode Transcript
[00:00:00] Speaker A: Foreign.
[00:00:14] Speaker B: Welcome to Base by Bass, the papercast that brings genomics to you wherever you are. Thanks for listening and don't forget to follow and rate us in your podcast app. Today we are diving into one of the biggest, most enduring mysteries in neuroscience. The big one, it really is how exactly do complex neurodevelopmental disorders. We're talking conditions like autism spectrum disorder and schizophrenia. How do they originate at the cellular level? What starts that chain reaction?
[00:00:43] Speaker A: Right, and it's such a challenge because the symptoms are so broad, so varied. But, you know, researchers have recognized this unifying feature for a long time. They often call these conditions developmental disconnection syndrome.
[00:00:54] Speaker B: Disconnection syndrome. So faulty wiring.
[00:00:56] Speaker A: Faulty wiring. Exactly. In the most powerful computer we know, if you actually look at the BR structure, you often see defects in the major connective highways like the corpus callosum. The corpus callosum is the perfect example. It's this massive bundle of millions of axons, you know, the communication cables that connect the left and right brain hemispheres.
In these conditions, that connectivity is often.
Well, it's abnormal.
[00:01:22] Speaker B: So you have this huge large scale structural problem. The brain literally isn't wired up correctly. But that has to start somewhere incredibly small. A single molecular glitch, maybe.
[00:01:32] Speaker A: It has to. And what if the key to this, this monumental architectural problem isn't some big messy failure, but something simple, a really precise molecular mechanism that just controls timing?
[00:01:46] Speaker B: Timing.
[00:01:47] Speaker A: Exactly. And that's what today's deep Dive reveals. We're going to see how a single disease associated gene basically takes control over the brain's complex wiring by micromanaging one of the cell's most ancient and fundamental tools, calcium.
[00:02:02] Speaker B: And this is where it gets really interesting, because that gives us a clear chain of command.
[00:02:05] Speaker A: It does. It offers this incredibly powerful resolution to a long standing question.
[00:02:10] Speaker B: Okay, so before we unpack that entire chain, we need to officially introduce the source material for this deep dive.
[00:02:15] Speaker A: Absolutely. This analysis is based on the paper titled CY FIP1 governs the development of cortical axons by modulating calcium availability, which was published in Nature Communications.
And we really want to celebrate the work of Carlotta Ricci Mailli, Julie Madroid, Federico Kaichi Tilman Axel Nuri Domingueza Tersa, and Claudia Bagni.
[00:02:36] Speaker B: A huge team.
[00:02:38] Speaker A: A huge team. And their work has just significantly advanced our understanding of this gene, CYFIP1, and its critical role in the timing of brain development.
[00:02:47] Speaker B: Okay, let's start with the genetics. For you, our listener. Why CY FIP1? Why did they zero in on this.
[00:02:52] Speaker A: One gene, it's all about location. You know, it's zip code on the chromosome. We're talking about a specific region called 15Q11 2.
[00:02:59] Speaker B: And that's a known hotspot.
[00:03:01] Speaker A: It's a major high risk zone. Copy number variations, or CNVs. That's where bits of DNA get either deleted or duplicated. If they happen in this region, they're associated with a much higher lifetime risk for both ASD and schizophrenia.
[00:03:13] Speaker B: Wow. So a single deletion or duplication there, and you're at high risk for two conditions that seem quite different on the surface.
[00:03:19] Speaker A: Exactly. And while there are few genes in that region, CY FIP1 is the one that's consistently flagged as the most likely culprit. So to understand the risk, you have to understand the gene.
[00:03:30] Speaker B: And what we already knew about CY FIP1 makes it sound like a cellular jack of all trades. It has this kind of dual identity, right?
[00:03:38] Speaker A: It absolutely does. CY FIP1. This stands for Cytoplasmic Fmrpe Interacting Protein 1. It's involved in two processes that seem separate but are both totally critical for a developing neuron.
[00:03:50] Speaker B: So let's talk about the first role.
[00:03:52] Speaker A: Its first role is structural. It's a key part of something called the wave E regulatory complex. You can think of CY FIP1 as being like the foreman on a construction site. This complex regulates actin polymerization.
[00:04:04] Speaker B: Actin being the cell's internal scaffolding.
[00:04:06] Speaker A: Precisely. It controls a cell's physical shape and movement, especially during growth. An axon literally can't grow without rearranging its actin cytoskeleton. So CY FIF1 is managing the physical buildout.
[00:04:17] Speaker B: Okay, so that's the structural part. What's the second job?
[00:04:20] Speaker A: Its second role is translational repression.
In this job, CY FIP1 binds to two other really important proteins, FMRP and EIF4E.
Together, they act like a. I don't know, a genetic librarian or maybe a sensor.
[00:04:35] Speaker B: Okay.
[00:04:36] Speaker A: They decide which messenger RNAs the MRNA's are allowed to be translated into proteins and which ones get silenced or maybe even tagged for destruction.
[00:04:44] Speaker B: So it's controlling both the physical structure and the expression of the genetic blueprint right there on site. That sounds essential for building something as long and complicated as an axon.
[00:04:54] Speaker A: It is. And crucially, the researchers weren't starting from scratch here. They already knew that. Having a CY FIP1 deficiency causes major issues in mouse models.
[00:05:03] Speaker B: Right. The CFIP1 heterozygous mouse. The CFIP1 plus minus model.
[00:05:06] Speaker A: Correct. And These mice have what we call strong face validity. They show behaviors that look a lot like ASD and schizophrenia. And their brains show reduced functional connectivity, structural problems.
But the one thing that was missing, the thing this paper gives us, was the exact molecular mechanism that controls the initial physical wiring.
[00:05:23] Speaker B: The how?
[00:05:23] Speaker A: The how.
[00:05:24] Speaker B: Okay, so let's unpack how they did it. If your goal is to pinpoint this incredibly specific molecular bottleneck, how do you even design the experiments?
[00:05:33] Speaker A: They used this brilliant sequence, kind of moving from the big picture in the whole brain all the way down to the individual molecular steps. They started with in vivo tracking the.
[00:05:42] Speaker B: In utero electroporation iue.
[00:05:45] Speaker A: Exactly. And IUE is.
It's a very technically demanding procedure. They do it at embryonic day 15.5 in mice, and it lets them deliver a fluorescent marker right into the specific neurons.
[00:05:57] Speaker B: They want to study the callicle projection.
[00:05:59] Speaker A: Neurons, or CPNs, the very ones whose axons form the corpus callosum. By making these axons literally glow, they could then track their growth as they cross into the other hemisphere at these really critical postnatal days. P5, P15, and P30. It gave them a timeline of the defect.
[00:06:14] Speaker B: So once they saw the problem in vivo in the living animal, they had to prove it was a problem with the neuron itself. Right. Not its environment.
[00:06:21] Speaker A: Right. A cell autonomous problem. That's where the microfluidic chambers come in. They cultured the neurons in these tiny devices that physically separate the cell body from the long axon.
[00:06:31] Speaker B: So you can study the axon on its own?
[00:06:33] Speaker A: You can study it on its own. It let them measure growth rate, watch things like mitochondrial movement, and confirm the defect was coming from inside the SCI FIP1 deficient neuron.
[00:06:42] Speaker B: So that handles the cell biology. How did they figure out which specific MRNA's CY FIP1 was messing with to cause all this trouble?
[00:06:52] Speaker A: For that, they needed their molecular toolkit. First up was RNA immunoprecipitation, or rnaip. You can think of this like casting a very specific fishing hook, the CY FIP1 protein, into a sea of MRNA to see what it bites.
[00:07:05] Speaker B: And what did it catch?
[00:07:06] Speaker A: It immediately pulled down several MRNA's that all encode subunits of voltage gated calcium channels.
[00:07:12] Speaker B: Wow. Okay, so it was physically grabbing the instruct instructions for calcium gates.
[00:07:16] Speaker A: Yes. And their next critical step was the actinomycin d assay.
Since Cy FIP1 is known to affect MRNA stability, they used this drug to stop all new RNA from being made.
Then they just watched to see how quickly those target MRNA's decayed.
It's a test of their shelf life.
[00:07:35] Speaker B: And then the final proof, the thing that connects it all, the chemical rescue.
[00:07:39] Speaker A: This was the definitive test.
They took their defective neurons and tried to fix them with chemicals. They used ionomycin, which is a calcium ionophore.
[00:07:47] Speaker B: It just shoves calcium into the cell.
[00:07:49] Speaker A: It just force feeds the cell calcium. Exactly. And they also use specific agonists for voltage gated calcium channels, things like BK8644 that propped the channels open. If adding calcium back fixed the problem, they knew they had found the bottleneck.
[00:08:03] Speaker B: So let's get to the data. What did that in vivo work actually show about the wiring process in these mice?
[00:08:09] Speaker A: The first major finding, and this is so crucial for you to understand, was a clear developmental delay. In the CIFIP1 deficient mice, the axon growth into the other side of the brain was significantly reduced at postnatal day five.
[00:08:21] Speaker B: So early on, very early.
[00:08:23] Speaker A: Then by P15, the terminal arborization. That's the complex branching the axon does to make connections. That was also reduced. The wires weren't getting across fast enough, and they weren't branching properly.
[00:08:35] Speaker B: But here's the kicker, right?
[00:08:36] Speaker A: This is the profound clinical takeaway.
[00:08:38] Speaker B: Yeah.
[00:08:38] Speaker A: By P30, the arborization normalized. It caught up.
[00:08:41] Speaker B: It caught up.
[00:08:42] Speaker A: This is so critical. It means CY FIP1 deficiency causes a developmental delay, not a permanent, irreversible loss of connections. The wiring gets done, but it's late. And that suggests the issue in these disorders is all about critical timing, that distinction.
[00:08:58] Speaker B: Delay versus permanent failure. That changes everything.
So let's zoom in. What was actually happening inside those delayed axons?
[00:09:05] Speaker A: The moment they looked in vitro at the earliest stages, around day three, they saw the power grid was in trouble. The mitochondria were sending out distress signals.
[00:09:12] Speaker B: The powerhouses of the cell.
[00:09:14] Speaker A: Right. And what they saw was that the axons from the deficient neurons had an increased density and weirdly, abnormal motility of their mitochondria. This hypermotility is a really bad sign.
[00:09:26] Speaker B: Why is that?
[00:09:26] Speaker A: Because mitochondria need to be anchored.
They need to be docked at specific spots along the axon to provide the energy for the growth cone to push forward.
[00:09:35] Speaker B: So instead of settling down to work, they're just running around aimlessly.
[00:09:38] Speaker A: That's a perfect analogy.
And the cause of this frantic movement? It was the calcium drop. The cyphap 1 deficient neurons had a significantly reduced concentration of calcium, both in the main cell body and specifically inside the axon. And even the mitochondria themselves were starved for calcium.
[00:09:55] Speaker B: And calcium is the master signaling molecule.
[00:09:58] Speaker A: It's fundamental. It regulates everything, including mitochondrial transport and docking.
Low calcium means the mitochondria never get the signal to stop and get to work.
[00:10:06] Speaker B: So low calcium, hypermodal mitochondria. What was the functional impact?
[00:10:11] Speaker A: The impact was severe metabolic distress. Low calcium led to reduced mitochondrial membrane potential. The battery wasn't fully charged, and that meant low ATP levels right at that critical P5 stage.
They even saw the mitochondria were physically larger and more elongated, which is a known sign of cellular stress.
[00:10:30] Speaker B: Okay, so the chain is built. Delayed wiring is caused by malfunctioning mitochondria, which is caused by low calcium.
Now, the smoking gun.
How does CYFIP1 control the calcium gates?
[00:10:43] Speaker A: This is where its job as the genetic librarian comes in. The Researchers show that CyFIP1 forms a complex with another set of proteins, the HU3 proteins.
And this complex is what acts on the specific MRNA's that code for the main subunits of the voltage gated calcium channels.
[00:10:58] Speaker B: Which specific channels are we talking about?
[00:11:00] Speaker A: They identified three main targets. CAC 9 or C, CAC 9E and CACNO1I. These are the actual pores that open to let calcium flood into the cell.
[00:11:08] Speaker B: So if CY FIP1 is the manager and the channel MRNA's are the construction permits, what happens when the manager is under resourced?
[00:11:16] Speaker A: Well, when you have less CY FIP1, it can no longer properly stabilize those permits. The lack of CY51 leads to their enhanced decay. They just expire too quickly and become unstable. They become unstable, and the result is fewer actual calcium channel proteins get built and inserted into the axon's membrane. Fewer gates means less calcium entry, and you get a starved, slow growing axon.
[00:11:35] Speaker B: That chain of command is just.
It's so beautifully precise. So what does this all mean for the big picture of neurodevelopmental disorders?
[00:11:45] Speaker A: It means we can finally establish causality.
[00:11:48] Speaker B: Hmm.
[00:11:48] Speaker A: And those rescue experiments, they prove it. When they used ionomycin to artificially raise the calcium levels, it fully restored normal axonal growth rates in the deficient neurons.
[00:11:58] Speaker B: Fully restored it? So just fixing the calcium fixed everything downstream?
[00:12:03] Speaker A: It confirmed calcium was the immediate critical bottleneck, at least at that specific early stage. The rescue was dramatic. It restored growth, it stopped the mitochondria from being so hypermodile, and it boosted their membrane potential. Wow. And what's more, they got the same growth rescue just by using the VGCC agonists, the drugs that specifically stimulate those channels. By propping open the gates, they fix the whole downstream problem.
[00:12:27] Speaker B: And again, it all comes back to timing.
[00:12:29] Speaker A: It all comes back to timing. All these defects, the low calcium, the low ATP, they were most prominent at those very early stages. Div 3 and P5.
Cy FIP1 is essential for the timely execution of this wiring plan.
If you miss that window, even if the connections form later, they might not integrate correctly into the circuits that are already developing.
[00:12:49] Speaker B: Which loops right back to the human conditions.
[00:12:51] Speaker A: Precisely. This delayed callosal development provides a concrete cellular reason for the connectivity defects we see in the adult mice, which, you know, mirror what we see in patients with ASD and scz. It really substantiates that idea of developmental disconnection.
[00:13:06] Speaker B: So for you, our listener, this research isn't just an explanation. It really points towards a potential therapeutic path.
[00:13:12] Speaker A: It really does. It suggests that CY FIP1 linked disorders might be treatable by restoring calcium balance, maybe by targeting these specific calcium channels. And since the core problem is a delay in a critical window, the goal wouldn't be to fix something that's broken forever, but to speed up a system that's just lagging behind.
So to summarize the central insight for you, the disease associated protein CY FIP1 acts as a molecular manager. It ensures proper brain wiring by stabilizing the instruction manuals, the MRNA's that build voltage gated calcium channels. And when you have less cy fip1, when you have less cy fip1, those instructions degrade too fast. That leads to low intracellular calcium, which causes mitochondrial dysfunction and critically, a delay in the brain's complex wiring process. And that delay sets the stage for these disconnection syndromes.
[00:13:59] Speaker B: That idea that the core defect is about timing and not total failure is, is it's transformative.
Which leaves us with this final thought. If the key problem is a developmental delay in a very specific early time window, how could future therapeutic strategies leverage that timing? How could we precisely correct calcium levels just when they're needed, before any irreversible connection issues arise? That's certainly something to ponder.
[00:14:25] Speaker A: This Deep Dive was based on an Open Access article under the CC BY 4.0 license. You can find a direct link to the paper and the license in our episode Description. If you enjoyed this, follow or subscribe in your podcast app and leave a five star rating. If you'd like to support our work, use the donation link in the description. Now stay with us for an original track created especially for this Deep Dive and inspired by the article you've just heard about. Thanks for listening and join us next time as we explore more science. Bass by base.
[00:15:01] Speaker C: Two quiet continents inside my head A pale white river where the long road spread I reach for the far side I feel it cold but something's still in a current after all Threads want to grow where the signals glow yet every step is slower than it should go There's a missing time in the bloodstream of the wire A dimmer spark inside the living fire I'm pushing forward but the lights don't rise like dawn with Hel behind closed eyes Send the cow to you Let it turn the key Open the gates and set the motion free Build me a bridge where the bright waves run so the two sides meet like a rising sun if the power fades if the fuel runs low Watch the pathways grow.
Letters in the cytoplasm Held to to lose Pages that should last Slipping from their use the doorway Protein start to fall away so less light enters where the engine stay and in the accent Little power trains drifting Rome but don't ignite the main so the travelers move on board untied so searching for a dock they can't decide but give them one clear pulse One honest wave and they remember what they're meant to say Send the cow let it turn the key Open the gates and set the motion free Build me a bridge where the ride waves run so the two sides meet like a rising sun if the power fades if the fuel runs low Bring back the current Watch the pathways grow.
Raise the room inside the cell tonight not by force by finding what is right A steady surge A measured blaze in the stalls Horizon starts to change Engines wake the shadows lift the drifting pieces Learn to shift in every delight Direction finds its a.
[00:17:59] Speaker A: As if the.
[00:17:59] Speaker C: Wy whispers back its name Send a castle Let it turn the key Open the gates and set the the motion free Build me a bridge where the bright waves run so the two sides meet like a rising sun From a quieter spark to a clearer glow Bring back the courage Watch the pathways grow.
Hold the line Let the living map unfold across the calcium bridge we hope.
