How do your industry PMMs collaborate with product- or sales segment-focused PMMs?

There are two questions here, and I'll address both. One answer is much shorter than the other.

How do we collaborate across industry and core PMM? Constantly. At Meraki, we do have an Audiences team focused on both industry and a few specific LOB personas. The give and take is pretty regular. We collaborate on content, messaging, and thought leadership to make sure we're helping attract and meet customers on their terms. 

That's the short answer. Your second question about being the first vertical PMM is more nuanced. To start, if your company is successful enough with a horizontal GTM, you've got a huge tailwind pushing you forward. There are probably already a number of high-profile wins you'll be building on. 

But, that also means you're going to have to be an evangelist, a change agent. I'd argue that the first thing on your agenda will be to understand the business's current understanding of your target industry(s). And then diagnose what poor assumptions they've made. 

It will feel like you're spinning your wheels, but you really have to dig in. Understand clearly the reality of the situation:

• What does product think the problem is in that industry? Do they think it's different, or the same?
• Why does exec leadership believe these industries are the right ones to tackle? Is it expansion or growth of existing? 
• What does sales think? What does the data say? Are these deals larger? Smaller? Harder fought?
• What industry-specific niche compeitors exist? Why are they better than you (they're better than you)
• And, finally, what do your current customers in that industry really think? What did they compromise to choose you? Why did they make that compromise? Would they make the same decision in hindsight?

From there, based on what you learn, you may need to go on a bit of an INTERNAL roadshow to convince everyone of the pragmatic reality of the market. Where are you strong? Weak? What are the actual problems customers care about? Is your problem high-priority enough? And, where are the key product gaps you have to cover to be competitive?

Once you have that, and you've given that ptich roughtly 3 dozen times, then you're probably ready to start really going to market with a revised plan of attack. 

Oh, and make friends with PR early. They'll be a huge asset in winning credibility in your market.